Passive Solar Design Overview – Part 1

Below the fold is a TOD:Campfire post on Passive Solar, from longtime TOD reader Will Stewart. Will is a Systems Engineer in the Energy industry - he will have a follow up post in the near future. Please add your own experience and expertise with passive solar, including links and images in the comment section - the sun is as close as we get to a perpetual energy we best access and take advantage of it is the subject of tonights post. For submissions to this series, please email or
Passive Solar Design Overview – Part 1

Passive solar refers to the design and placement of a building to enable solar heating without the need for sensors, actuators, and pumps, in contrast to active solar, which utilizes pumps/blowers, sensors, and logic control units to manage collection, storage, and distribution of heat. The two techniques are not exclusive, however, and can work together effectively.

As solar radiation (insolation) is a diffuse energy source, and not at the beck and call of a thermostat, passive solar design techniques are at their best when combined with other related methods, such as energy efficiency (insulation, weatherization, building envelope minimization), daylighting, passive cooling, microclimate landscaping, and a conservation lifestyle (i.e., temperature settings, raising and lowering of insulated shades, etc). Most of these topics will be covered in other articles, though passive cooling will be addressed in this series, which is intended as an overview, as a complete engineering treatment on passive solar design would require several dozens of articles.

Even though solar insolation is diffuse, and generally weaker the further away from the equator, it can be the basis for the majority of a building's heat energy input even in high latitude places such as Canada, Norway, Germany, the Northern US (Maine, New Hampshire, Michigan, Wisconsin, Minnesota, North Dakota, Montana, Idaho, Washington state, etc), Scotland, the Netherlands, etc. Even the US Department of Defense has a passive solar design guide. Design approaches such as Passivhaus have achieved up to 90% reduction in energy use over traditional building methods. In areas with reasonably consistent winter insolation, well insulated passive solar buildings with sufficient thermal mass storage can approach 100% of their space heating needs with passive solar. Enhancements can be added to existing buildings, through major or minor renovations, or through simple additions (Part 4 of the series).


The Greeks faced severe fuel shortages in fifth century BC, resorting to arranging their houses so that each could make maximum use of the sun’s warming rays. A standard house plan emerged, with Socrates noting, “In houses that look toward the south, the sun penetrates the portico in winter.” The great Greek playwright Aeschylus even proclaimed only primitives and barbarians "lacked knowledge of houses turned to face the winter sun”. The Romans picked up on this technique, and improved it by adding windows of mica or glass to better hold in the heat. They passed laws to protect the solar access rights of owners of solar homes from shading by new buildings. In the Americas, the Pueblo and Anazazi took advantage of solar insolation in their adobe and cave dwellings, respectively.

In the 18th and early 19th centuries, solar greenhouses became popular for those of means to grow exotic tropical plantlife in temperate climes. In the 20th century, German architects such as Hannes Meyer, director of the influential Bauhaus architectural school, urged the use of passive solar design techniques that began to flourish in the 1930s, only to be pushed aside by the Nazis and WWII. Many German architects made their way to the US, and a small solar market developed. Built in 1948, Rosemont elementary school in Tuscon obtained over 80% of its heat via solar means, but in 1958, with cheap energy now available and an extensive addition planned, the school district chose to go with a gas-fired furnace. The 1970s saw more emphasis on renewable energy, and passive solar became a household word, though still only penetrating a very tiny percentage of builders’ visions for the new homes market. More in-depth passive solar history details can be found at the California Solar Center.

The Basics

Location and Orientation

To assess whether passive solar is advantageous to a location, one must first find out the amount of winter sunlight that is available. The simplest way is to find solar insolation data for the site under consideration, ideally collected over a series of decades (noting that a changing climate can mean the data may need to be extrapolated). The data can come in tabular or map form, with the latter providing a quick indicator of the amount of winter insolation in one's area. Tabular data, however, is more precise, giving one the best information available about trends in their area. A note of caution: the data is usually an average of conditions, and does not necessarily take into consideration unusual weather years or how the climate may change in one's area of consideration.

Interpretation of Data:

Most of the maps and tabular data measure solar insolation as kWh/m2/day, which is roughly the number of kilowatt hours of energy striking a square meter of surface in a day. This is also referred to as a Sun Hours on some maps, and we will refer to it as such throughout this series. Important note: Since virtually all modern passive solar design focuses on vertical windows, data must be specified or converted to a vertical orientation. Some of the data currently available is for collectors tilted at an angle equal to the site's latitude (L) or a horizontal surface (H), which would need to be converted to a vertical surface (V). The table below contains a partial list of solar maps and data, though make sure any source you use focuses on winter data, as other maps/data are used for year around solar photovoltaic projections.

Region Maps Data
World - Solarex (L)
- FirstLook (Americas only currently)(H)
- WRDC (select Global)
Canada - Solarex (L) - WRDC (select Global)
Europe - Satellite data map (H) - WRDC (select Global)
US - National Renewable Energy Labs
(select Vertical surface) (V)
- Many US cities (H)
- Detailed data (H) (manual)
- Other sources
Australia - Aus BOM June Map (L) - Aus BOM site data (L)

The orientation of the building will determine how much solar insolation is captured during the desired period of the day. For example, a passive solar house facing the equator will receive an equal amount of solar heat before and after noon. The more a building is oriented away from true south (or north in the southern hemisphere) the less winter solar insolation it will be able to capture, and it becomes more susceptible to undesirable summer solar energy that is harder to shade with a properly sized overhang.

In addition to direct solar insolation beaming from the sun, there is also diffuse radiation from the sky, and reflected radiation from the ground.

Figure 1 - Types of solar input

Design Aspects:

Passive solar building design revolves around 5 main aspects;

Aperature: The set of windows and overhangs that determine how much sun enters the building.
Absorber: The material that the sun’s ray come into contact with.
Thermal Mass: The material that stores the sun’s thermal energy for re-release after sundown.
Distribution: The means by which the thermal energy is released to the living/working spaces.
Control: The techniques used to control the collection and distribution of the sun's thermal energy.

These aspects can be configured by the designer/architect into roughly three main design themes (with endless variations);
  1. Direct Gain: Sunlight shines into and warms the living space.
  2. Indirect Gain: Sunlight warms thermal storage, which then warms the living space.
  3. Isolated Gain: Sunlight warms another room (sunroom) and convection brings the warmed air into the living space.

Figure 2 - Direct solar gain

Figure 3 - Indirect solar gain

Figure 4 - Isolated Gain

In Part I of this series, we will cover the Aperature;


The first step in passive solar design is determining how to collect the sun's energy. In most climates that passive solar is employed, this means windows of one form or another. An important metric of a window is its Solar Heat Gain Coefficient (SHGC) that measures how much of the sun's energy passes through the window without reflection or absorbtion and re-radiation. The higher the SHGC, the more solar energy a window will allow through. A plain single pane window normally has a SGHC of 0.86 while a plain dual pane window is about 0.72.

In order to reduce heat loss in cool and cold climates, windows are normally at least dual pane, if not triple pane. The dead air space between window panes helps to increase the insulation factor, call the R-value (or its inverse, the U-value). One single pane of ordinary glass has an approximate R-Value of 0.85. A dual pane window with 3/8 inch of air space typically has an R-value of 2.1. The substitution of less viscous gases such as argon and krypton allow greater distances between panes before the gas begins to convect (tranferring heat at a much higher rate), increasing their insulating effect. Each pane added, however, blocks/absorbs/reflects more solar energy, which effectively reduces the window unit's SHGC. Additionally, low-E coatings that help to reduce the amount of infrared heat radiated out of a room through a window also reduces SHGC (amount dependent on the type of low-E coating). So a balance must be struck by the designer/architect between the amount of energy received during winter sunlight hours vs. the amount of energy lost 24 hours a day. There are windows available that have been designed for passive solar applications to provide sufficient SGHC while still providing adequate insulation (e.g., one such window has a SHGC = 0.56 and an R-value = 5).

There is ongoing research to bring aerogel windows to commercial production, as these windows provide extremely high R-values (approximately R-10 per inch) while having SHGCs of .52 or greater.

The orientation of the window is just as important; windows facing the equator receive the greatest amount of sunlight. And this orientation also greatly reduces unwanted solar collection during the warmer days of the year, as windows facing East and West are difficult to shade effectively with simple overhangs, requiring larger and/or view blocking awnings.

California Solar Center: Passive Solar History
US DoE Passive Solar Home Design

One of my web sites plots the exact angle of the sun for any location in the United States

There is a dropdownlist with major cities, and you can enter any coordinates.

I built this site for photography purposes, and I learned quite a bit when actually crunching the numbers. The azimuth angle for sunrise (and sunset) varies by 57 degrees between winter and summer solstices in Dallas, for example. That explained why my apartment bedroom, facing about 10 degrees north of due west, is a nearly-uninhabitable furnace in the summer but is freezing cold in the winter since the sun is too far south to provide any warming.

Can the author or anyone else, give me some ideas of how to intelligently use thermal mass in building envelope heat transfer calculations. Or maybe some rules of thumb. I've been scratching my head and searching the internet and text books for way's to estimate how thermal mass contributes to overall heat in a building.

The way I see it, thermal mass is most useful in a building that is continuously occupied or heated. Since if you have to keep re-heating the thermal mass every morning, you lose out on it's storage advantages.

I'd like to evaluate whether it was wise to build a rock wall inside my office cabin that is only heated by wood and occupied about 8 hours a day. But, I haven't been able to figure this out in real numbers.

Any advice or help on this would be appreciated.

Thermal mass will be in Part 2 of this series. It will be at the overview level, but I will be referencing other sources that give volumes of information on materials and calculations.

As a short answer, the thermal mass in your situation could help keep the cabin warm if the fire was allowed to burn out early (x hours before you left), depending on how much mass there was, the temperature it reached, and where it was located. The downside is it takes a little longer to bring the cabin up to the desired temperature.

Will, could you list the parts to come? It might save you some unnecessary questions from readers, as well as give an opportunity for suggested areas you might not have planned that you or others could cover.


Nothing is written in stone at this time, though Part 2 will focus on Absorber and Thermal Mass. Later in the series, the rest of the Design Aspects will be covered, as will renovations, passive cooling, design tools, design examples, standards (i.e., LEED, Passivhaus, AIA 2030, etc), and examples of existing passive solar buildings.

Just a peeve, but in future parts will you please spell "aperture" correctly?  This grandson of an English teacher finds it grating.

Funny, as an English teacher, they don't bother me unless they are very basic, such as their/there. English spelling is insane. Since I'm not always sure who is a native speaker and who isn't, I don't often sweat it. When the content of the post reflects a lack of intelligence, then the usage and spelling can help suss out who is and isn't worth responding to.


Just a peeve but aperture is spelt correctly in the majority of cases in Will's document.

May I inform you of a beastie called "the typographical error", often found lurking in "documents",
like brontosauruses, they only eat grass - no need to panic.

Oh shit I've just been trampled by some brontosaurii.

The moral to this story is, of course: "don't grow lawns".

Hi Will,

Something else to explore here is the availability (or lack of) proven solar house designs.

All the solar homes I have visited seem to "sort of work", or "work nice, except in ", or "don't really work, but look nice".

As a designer myself (but not of homes) I think that the problem is that the prototypes are too expensive. Architects and do-it-yourselfers read up on passive solar design, starts sketching, throw in some changes at request of the buyer or to cut costs or for styling, then build the house. And then it doesn't quite work - but are they going to take their expensive new knowledge and build another passive solar house just like it but with corrections? No, they will either never build another or the next one they build will be so different that the lessons they learned last time barely apply.

What is really need are completely detailed proven designs that all you need to do is site it at the proper orientation. Complete blueprints and specs for everything - no substitutions or changes required.

A private home that is also an energy collector is TOO EXPENSIVE for experimenting or prototyping - it needs to work right the first time. And then maybe people would be more willing to contract a new solar home if they could visit a model house, talk to the residents, see the utility bills, and then be confident that they would be buying an exact clone.

Do such proven home designs exist?


no substitutions or changes required.

I was with you up to this point. Yes, there are some stock house plans, but they need to be tweaked depending on the climate (i.e., solar insolation, temperature, wind profile [infiltration loads], etc) of the location. We'll look at some case studies later in the series.

I’m just an amateur (hobbyist) home builder so I’ll apologize in advance for lack of technical detail. But, I’ve been very interested in passive solar homes since the 70s. My wife and I built (with our own hands) a cabin a couple of miles from the south shore of Lake Superior. The design looks identical to Nate’s diagram except that it had no thermal mass. At 25 degrees (F) below zero the cabin was toasty warm when we had a bright sun and lots of reflecting snow. A half hour after the sun went down we lost all benefit of solar heating.

In the early 80s we decided to build a house 20 miles north of Milwaukee, WI. Again, we used a passive solar design but this time with lots of thermal mass.

Here are the most important details:

We read an article about a Los Alamos Testing Lab experiment where they determined that a 4 inch thick monolithic film of concrete on ALL surfaces except the glazed south exposure was optimal for thermal mass.

We read in a brochure from Portland Cement Assoc about a fellow named Champion who built tilt-up concrete motels across the Southern US. We decide to build the basic structure by copying his methods. Our floors and ceilings are 6 inch concrete and the walls are either 6” or 8” concrete. We (wife and I) cast all the slabs in our yard – one on top of the other with a bond breaker in between. A huge crane lifted all parts (some 20,000 lbs) into place and we bolted or welded it together. We used a Colorado company for all the lifting and bolting hardware and gadgets.

We read a lot about super insulation. There are 2 buildings – the house and a detached garage-workshop. The house has 12” of fiberglass insulation. The workshop has 2” of Dow Foam and 6” of fiberglass (this is the best).

Wife is an incurable romantic and insisted upon an old-fashion appearance with a turret, stucco, etc. On top of the insulation layer is a half inch of oriented strand board and one inch of old fashion cement based stucco (again we did all the work ourselves – as we did for most of the construction process).

The “basement” is a 4 foot crawl space (all concrete) that acts as a heat plenum for a boiler system. Fans blow air thru openings in the first floor – all other heat distribution is just natural air flow.

Glazing is double pane with 80% of it facing due solar south (as measured at solar noon).

Floors are ceramic tile and walls are skim coated plaster with a sound absorbing pattern (very, very important).

Windows have blinds but not the insulating ones we hope to install “some day”.

The house seems to work pretty well. Summer cooling costs are very low as we normally cool at night and close up during the day. Thermal “fly wheel” of the concrete really keeps it cool on hot days. We have a small window air conditioner in the bedroom that we run a few days each summer.

Winter heating is really dependent on the amount of sun. Bright days mean no furnace time at all regardless of how cold it is outside. Extended cloudy periods result in almost no benefit from the design of the house. However, there are almost no drafts, the heat is extremely even and it is comfortable in this house at a lower temperature than in conventional houses – I suppose because of the way the heat radiates from the concrete.

As I said, I’m just an amateur and we never had an architect or builder – I was fortunate to work at a technical college and got lots of expert advice. I also passed all building inspection licensing tests for WI – helps when talking to the local building inspector. However, I have almost no information of a comparative nature about the effectiveness of this design or any kind of cost-benefit analysis. I understand Greg’s question and often wish someone would evaluate our effort after living in this house for 26 years. All I can really say is that it is a wonderful house to live in – but we still have higher heat bills than I originally anticipated.


Amazing work for an 'amateur' home-builder. How do your heating bills compare with your neighbors who have a similar square footage? Insulating shades could make a tremendous difference.

Hi Will,

I wish I could answer that question with quality data - but I only have some casual observations. First, our total energy bill for 8 months out of the year is minimal - March to Oct. And I do know that some of our neighbors have significant energry bills for that period - both heating and cooling. For Nov thru Feb my guess is that we are about half of our neighbors bills. Originally, back in the 70's when we got the first oil crisis, I wanted to build a house that could get by with no additional fuel source. My guess is that if I tried that, the house would not freeze - but it would not be a very pleasant experience - maybe it would "float" at about 40 degrees in mid-dec to mid-Feb.

I think you are right about the insulating shades. Originally, we bought some great fabric for making such shades - and designed window valences to accommodate them. Umh.. the fabric is neatly stacked in the attic at this time. As you can tell from my handle, bicycling is my first passion and I only work on the house to the extent that it does not interfere with the rest of my life too much - I think this is what has kept us happy with this unending building project (woodworking - cabinet projects never seem to end). As energy costs go up, I think these insulating shades will definitely rise up on our priority list of projects.

One of the issues that I researched nearly 30 years ago was the depth of the air space between the double panes. The wisdom of the day was to have a 3/4 to 1 inch space. I had custom commerical panes made with this space (the glass itself is almost industructable in these critters). However, fogging with these windows has been a problem over the years. Economical replacements have a much smaller spacing (and more fragile glass). Has there been any more research on the space between panes that yeilds the best R value and solar effectiveness?

Has there been any more research on the space between panes that yeilds the best R value and solar effectiveness?

Yes, and it's much less than 1 inch.  If you have too much space between the panes, you allow enough space for convection cells to establish themselves and transfer heat.  Modern windows have either 3 glass panes or a plastic film in the middle to break the convective path and reduce the heat transfer rate to close to the rate of diffusion.

Right. Argon has a better thermal resistance than air and is less viscous, so will convect less. Immobile air has far greater thermal resistance than convecting air.

Adding more window pane layers will reduce heat loss, but will also reduce SHGC. An examination of window manufacturer's offerings in the context of one's overall building shell UA and specific climate (and other window treatments, such as insulating shades) would be the next step.


Window Glazing U-value R-value
Double glass, e = 0.10*,
1/2-inch air space
0.37 2.7
Double glass, e = 0.10*,
1/2-inch argon space
0.34 2.94
Triple glass, e = 0.10* on 2 surfaces,
1/2-inch argon spaces
0.23 4.34

Hi Bicycle Dave..

...fogging with these windows has been a problem over the years...

I had the same problem with one of my windows. I replaced a fogged vacuum panel once with an identical vacuum panel, but that too fogged after about 5 years or so.

I subsequently had the whole set of windows replaced, as the frames were past their sell-by date and the windows were really ugly as well as being fogged (1970s aluminium ugh!).

During the pre-replacement inspection I was told that fogging can be caused by insufficient drainage around the vacuum panel, leading to the insulating and bonding layer between the two panes of glass being subject to attack and deterioration over time.

It is therefore a good idea to ensure that the rebate round the glass is properly drained and ventilated so that the panel remains dry round the edges. The (hardwood) frames surrounding the new panels have small drainage holes at the bottom of the panel.

Hope this helps in the future



Your house is so beautiful it makes me green with envy.

I suspect that some improved materials like heat-mirror or aerogel windows would ameliorate most of your perceived deficiencies.

I realy like your design! It sounds sturdy, fairy unexensive, well insulated and you cant get too much thermal mass.

But how do your ventilation work? Do you have any heat recovery on the air leaving the house such as a heat exchanger warming the incomming air or a heat pump?

Your comments are rekindling my motivation to address some the energy conservation factors have been moved to back burner for several years (4,000 miles a year on a bicycle does take some time!)

Your comments have reminded me that we really need to finish the insulated drapes, start replacing windows that have failed (fogged) with better glazing, and deal with the whole issue of air movement. The first two issues are straight forward - I just need to do the work!

The air issue, however, is more complicated. It is also an area that I suspect could provide for a lot of savings. The boiler is in the garage-workshop building (which is also heated and stays very warm with a minimal amount of the hot water from the boiler). An underground pipe brings the hot water into the concrete crawl space in the house. Those finned gadgets and fans pull the heat from the hot water into the crawl space. From the crawl space the heated air, and radiant heat from the concrete, migrate into the the rest of the house on a pretty haphazzard basis. We actually have 3 floors with a rough finished (but well insulated) attic space as our computer room and storage area. This attic is always the warmest room in house (which is nice when sitting at the computer) but is definitely wasting heat. My original plan was to use a duct and fan arrangement to recycle the air from the attic to the crawl space - I need to finish this work. Aside from that, I'm not sure what else might help conserve heat? The boiler in the garage building (which was the smallest size available) just uses avaiable air. It is a "very high efficiency" boiler - according to the 25 year old brochure - and has some fancy piping to get every last BTU out of the heated water. The plastic exhaust pipe is never very hot. The house itself does not use outside air as part of the heating process - except for infiltration issues.

My decimated 401K, harsher winters these past two years, and rising fuel costs are compelling me to revisit some of these original ideas that have been back burnered for way too many years. The good news of being a do-it-your-selfer is the fact that we have no mortgage, the bad news is the snail pace of progress! It is also easy to become complacent when your living space becomes very comfy and nothing seems too urgent - until that January heat bill arrives!

You are a lucky man, every year I waste a few days planning a house and then throwing the plans away since I dont have the time or funds or need for realy building a house.

Where and how do the ventilaton air leave your house? Is it possible to get the heat out of the air before it leaves the house?

Are there insulation between the crawl space and the ground? If not you have a major heat leak, especially since it seems like you heat your house by heating air in the crawl space wich makes it one of the warmest parts of your house. You can probably add a layer of some dense styrofoam on the crawl space floor.

Btw I recenty visited some friends that recently had moved into a house built in the 1990:s. It is a two floor house probably made out of prefabricated concrete slabs and the slabs between the two floors were hollow and used to distribute hot air to all rooms. They had a central heater using hot water from the district heating system with a heat exchanger that sucked air from one point of the house plus the bathrooms. It were built as a pair-house sharing one outer wall with a neighbour and thus removing about 1/5 of the heat loss. Super insulated windows but not super insulated walls and no features for passiv solar. A few tweaks in the design, mostly with more insulation, and it would be an exellent passiv house. It had a carport for one car and a 10 A 240 V outlet intended for a block heater but obviously usefull for future plug in wehicle. It were built in an USA inspired urban area with cul-de-sacs and all but the planning is dense with small lots, a complete bicle lane network, child care and schools within walking or short bicycling distance and a train station within 5 km. It were obviously intended for families with one car that mostly use the bus service or bicycle to work and school.

Hi Magnus,

There were several years of pretty heavy duty construction projects going on in our house when my wife would seriously contest the "lucky" part! However, we would do it all over again and now enjoy the benefits of our labor. BTW, we never had more than a couple of nickels to rub together at one time - we just worked our way up to building a new house by rehabing run-down old houses in good neighborhoods. Our first house cost $17K - we borrowed money from friends for the down payment along with the GI bill loan arrangement. I know the whole marketplace has changed from when we started doing this, but I wonder if this is not one of those opportunities to get into some very afforable existing homes? Especially in the kind of setting that is often mentioned on TOD (small, dense, semi-rural towns).

I can look into the air intake for the boiler in the garage building - but the bigger issue is the house building and there ventilation is just from normal infiltration. Actually, some of the windows were "shop-built" by me (curved top windows in the turret) and are probably leaking a lot more air than they should.

The crawl space was heavily insulated - 2 inches of foam (DOW pink) under the floor and 4" of foam outside of the walls. I suspect that the main problem with the crawl space is that I'm not circulating the warm air in and out of there as aggressively as I should. It is always really warm down there.

Thanks for your thoughts.

I mostly wonder where the air leaves you house, not where it enters it.

One common ventilation system for factory built houses in Sweden is to have a lower airpreassure inside the house and air entering the house thru small regulated orifices and unplanned leakage and leaving the house via a heat pump with the ventilation fan. The heat pump recovers the heat in the exiting ventilation air and makes hot water and part of the heat for water radiators. Then there are resistive heating or an additional ground or extrenal air source heat pump loop used for the rest of the heating need.

This system is not the best one since you need to make fairly warm water as tap water wich makes the heat pump less efficient. It might be possile to retrofit such a system to your house to recover the heat in your ventilation air. The economics depend on the cost for electricity and your boiler fuel.

2 inches of foam below a ground slab is not much. Over here are 8 inches normal and people sometimes use more but then you can get a problem with the winter chill seeping under the house and freezing the ground below it, this is solved by adding a horisontal layer of insulation slightly below ground around the house. But anyway, the first inches are the most important ones.

Thanks for the comments - I'll have to look into these ventilation concepts. Truthfully, this is one area where I have little knowledge - but, I'll try to correct that.

The 8" foam under the slab is quite a surprise. I grew up in Duluth, Minnesota (lots of Swedish people) and also lived in northern Wisconsin before buiding here in southern Wisconsin - a little over 100 miles north of Chicago. Until we built our house, I never saw any insulation under a basement floor. Not many single family homes are built as "slab on grade". Even commerical buildings, where slab on grade is more frequent, put much (or any)insulation under the slab. In our case, with a 4 foot crawl space (used as a heat plenum) the 2" of foam was almost unheard of when we built. I'll have to check if any local builders are putting foam under the basement floor - but, I've never noticed any (other than ours). I've noticed that some high quality homes being built in this area now use 2" foam (R10) on the outside of the basement walls - but ours is the only one I know of that used 4". Guidlines are hard to come by for R value insulation of basement and crawl space walls here in Wisconsin. R15 seems to be a common recommendation (which would be 3" of the R5 foam board that we used) - but I doubt that many new homes even meet that recommendation.

I live in a house in extreme weather conditions. It works VERY WELL. I don't have time to explain many of the details. Suffice it to say it is a BERM house with dirt on three sides, south facing, double-pane windows. Without heat overnight, the temperature does not drop below 60 degrees F even as the outside temperature approaches 0 degrees F. A wood burning stove is sufficient but is supplemented by natural gas at this time. Concrete slab, much foam insulation on both exterior walls where dirt abuts and on interior concrete walls besides ordinary stud construction. Approximately R19 in attic; clearly a weak spot.

Exactly. Last year I moved into a solid brick built Edwardian house and for a while had the time profile thermostats set to the exact times I needed the heat. That is on at 7am off at 9am, then 6pm and 11pm for the evening. Trouble was it was still cold at 8pm when we were using the living rooms and was uncomfortably warm to sleep even until 1am.
It took me a few weeks to figure out the settings needed to be 4am/6am and 3pm/8pm - it's not intuitive coming from a 1990 built apartment that heated from cold in 30 mins. My garden office is new school however and goes from 8c setback to 22 in 20 mins flat with my heat pump. It is super insulated though and wont drop more than 8c overnight.
I also have the complication of underfloor heating in 2 rooms which is the ultimate thermal mass - 20 tonnes of concrete :) In this case I don't bother with AM heating as it is still warm and setback is 17 rather than 15 for the rest of the house. PM heating is on at 3pm again and off at 8pm - you can choose a lower steback but would then probably need to heat in the AM and for longer in the evening.
I have to use a gas fireplace to boost in unusual weather due to the slow response time.

I also have a house with tons of thermal mass (solid brick Georgian colonial, plus on top of that cast iron hot water radiator heat. It literally can take 3 hours to raise the temperature from a cold start even two degrees. I also find that there's an overshoot problem, where the heat from the radiators takes so long to affect the thermostat sensor that it goes a degree or two past the setting.

I look forward to the rest of this series. I have a sunroom on the south-facing side of the house with little insulation that really does a remarkable job of providing supplemental heat to the house on sunny winter days. I have to address the insulation problem, of course, so that heat isn't lost back out at night.

Combined with the wood stove being installed later this month, I'm hoping to almost eliminate our oil usage.

Comfort depends largely on the temperature of surrounding surfaces. That's why air temperature can be low if there is a warm spot nearby (stove or radiant panel) and occupants will be comfortable. Large cold masses are not what you want. It averages out. A lightweight curtain you can pull across a large (cold) glazed area on dark days or rug you can throw on a concrete slab are things that will affect sensation of comfort

A lot of mass in a cabin only used a few hours a day will probably not work well. Better to build a well insulated lightweight structure (or inner room) with lightweight surfaces where you can raise the average surface temperature easily.

My home is a superinsulated and massive structure with a glass curtain wall facing south. It will hang out at 50-55F in the winter with no inputs beyond internal gains, even through a string of gray Maine days. That's not comfortable. [It's nice to know the doomstead needs no heat worst case.] My office within, however, is next to wood stove and has lightweight surfaces. I'm further wrapping that part of the core with an additional "envelope" - an unheated but enclosed porch. If the sun comes out, the house goes to 60F quickly - a small gain - but the solar insolation raises the sensation of radiant warmth and it's quite comfy. Sunglasses optional.

Mass doesn't save energy. It's a way of modulating inputs. Pay attention to ambient surface temperatures. That's your comfort.

There were all sorts of publications in early 80's and I've not seen anything new that surpasses the work of that period. "Other Homes and Garbage" comes to mind as one of the best.

cfm on another gray day in Gray, ME

Thanks Will, It's exactly those types of hard numbers I'm trying to figure out. I know this will be an interesting heat transfer problem as it won't be steady state.

But if I could estimate the amount of heat that a certain mass could absorb, that takes care of the heating problem. My issue is how do you estimate how much that mass releases and at what rate, which would change as the air temperature changed...

Are there any HVAC engineers out there that have seen software that will account for non steady state heat transfer in buidlings using thermal mass? My work related heat transfer is limited to oil/gas facilities and exchangers, this is all new learning to me.

I also wonder about how to account for radiant barriers. I built my office with 12" thick walls and put a radiant barrier in all the walls and the ceiling. Problem is, typical heat trasfer calcs for building envelope are done utilizing R-Values which are conduction based (my assumption), so how does one account for a radiant barrier?

Studies on the thermal mass effect have been conducted on aerated autoclaved concrete. They are available on the web and I will post a link when I find it.

The studies I've seen show results for several large cities in different climate zones (Minneapolis, Atlanta, DC, Atlanta, Phoenix, etc.) Energy savings are typically about 8-10%. Savings are greatest where day and night time temperatures are greatest.

I built an AAC house with about 200 tons of mass on the Alabama Gulf Coast. Half of the mass is in the slab and earth underneath, which is insulated by the AAC foundation wall. The other half is in the 12” walls and 8” AAC ceiling panels over halls, closets and bathrooms.
I could not be more satisfied with the comfort level, and my utility bills are very reasonable. Last year I used 8500 KW and 200 therm of nat. gas for a 2100 sq ft house. Some of the savings are due to a high efficiency heat pump with gas heat below 40 F; however, heating is not an issue with this house in this climate.
Also important is the window area (320 sq ft) and window placement. The overhang on the south side is 30 inches and the lowest windows are 32 inches above the floor. The east and west facing windows are placed just below the eave and are only 3 ft tall. This keeps out summer sun. There is a picture window on the south wall recessed 4 feet in from the 30" eave. It gets only winter direct sun, but was really designed for the view.

Many friends and relatives build beautiful homes with large windows only to find out that unwanted sun caused overheating. So the windows are covered with drapes and the house is still hot in summer and cold in winter. Being a hobby photographer with an eye for light I carefully placed windows to minimize dark areas. A long, narrow house helps. Maximum interior distance from windows of about 12 feet works well. Also use white walls.
Concrete houses have minimal air infiltration and block out outside noise.
I designed the house myself (that is I drew up the plans in AutoCAD) and used a crew who specialized in AAC for installation of the walls and ceiling panels. Designing and building was not an easy project because the local architects and subcontractors were unfamiliar with AAC. Cost were about 50% above conventional construction (excluding my time as general contractor), in part due to standing seam aluminum roofing and high quality windows, doors and plumbing. The cost has to be weighed against the fact that the house has no exterior surfaces requiring painting (no wood), a 100 year roof and the house is fire proof, termite proof, rot and mold proof and storm resistant.

The things I would do differently are not using AAC for interior walls/ceiling panelsand keeping the size down to about 1500 sq ft.

Many friends and relatives build beautiful homes with large windows only to find out that unwanted sun caused overheating.

This can also happen with passive solar homes if there is too much south window area (north for the southern hemisphere) or too little thermal mass.

I looked at AAC when building my house, though couldn't find anyone around to supply it or install it.

Here is a link to the study of thermal mass AAC energy efficiency:

There is factor called DBMS (Dynamic Benefit for Massive Systems) that can be multiplied by the R value of a masonry wall to determine the effective R value. Atlanta=1.91, Denver=1.84, DC=1.67, Pheonix=2.53, Minneapolis=1.43, Miami=1.62. This is an oversimplification, so be sure you do enough reading to understand how to design HVAC for thermal mass. Thermal mass should be on the inside with the outside isnulated. AAC is an insulating material.

Also note that special software has been developed to analyze thermal mass in calculating energy consumption in buildings. I didn't use it myself because the above paper plus an Excel spreadsheet using the standard formulas was sufficient.

Thermal mass buildings require downsized HVAC systems, particularly the AC portion. Longer run time will do a better job of dehumidification. Most AC units are oversized and do a poor job of dehumidifying. I would recommend a variable speed air handling unit. They are quieter and more energy efficient.

My HVAC is 2 tons and gas furnace is 50,000 BTU/hr. The HVAC runs for a couple of hours at a time during the hottest part of summer, so the size is adequate. AC does not run much after sunset. Same with heat, mainly because heat is turned down to 68 F at night. (Climate zone is AL Gulf Coast)

The house temperature will stay constant for long periods. A cold front with lots of wind will not change the inside temperature enough to make the heat come on during the night.

Because of the near constant temperature and lack of drafts the thermostat settings can be kept at 76 summer and 70-72 winter with no discomfort.

I believe I saw software for analyzing thermal mass heating and cooling advertised in the publication "Concrete Homes", which I highly recommend to anyone interested in this type construction.

Haveblue. I don't have the numbers, but this information might be associated with your question. In 1999, I participated in a Cool Temperate Permaculture course in Australia. It was very 'hands on' and our facilitator had built himself a very cosy solar passive house. In that house he had a half wall made of mud bricks that was filled with water. The wall was located so that it received maximum direct, and diffuse sunlight in the Winter via a roof window orientated on the northern roof of the house. During the warmest parts of the winter days, the wall would absorb heat,then during the late afternoon/evening re-radiate heat back inside the house. Hope this is helpful. For more info try a Google on Australian Cool Temperate Permaculture NSW.

There is a superb must buy book called "The Passive Solar House"by Jack Kachadorian now in a revised form which has tables and calculations galore to help you estimate the various contributions of mass, window orientation, thermal gain and so forth. He emphasizes the importance of solar mass and I have used his ideas in home construction here in Jackson Hole, the icebox of Wyoming. His new edition has software to speed up the calculations. His basic idea is to have a concrete floor over a concrete plenum of 12" concrete blocks with vents around the perimeter to distribute air flow largely by convection. Added thermal mass under the concrete floor is in the form of sand or gravel. The foundation is highly insulated concrete mostly in the form of blueboard placed outside and under the foundation and floor. I have made many mods to Jack's Ideas, some successful, some not but his solar slab concept is stunningly effective especially when combined with the other passivhaus concepts of a tight building envelope R40 walls and R60 roof, efficient heat exchangers and solar water heating. I favor spray urethane insulation on virtually all insulated surfaces. It is difficult to build a tight house using other insulation. It is the standard for refrigerators and that itself should tell you all you need to know.

Thanks for your work on this Will.

I find myself riding around town looking at buildings this time of year and thinking about how well oriented they are, what kind of shape they are in, and considering whether they will be worth keeping around absent fossil fuels.

It is quite rare to find any house or building that is well situated. Most have some issue, such as facing the wrong direction with their long axis running north-south, severely shaded by adjacent buildings or evergreen trees, or windows on the wrong side for solar gain.

I wonder if any municipality has done an inventory of existing building stock with an eye like this and whether any building codes actually require passive design?


I haven't looked for municipalities that have inventoried their passive solar homes, though there are some that have codes/ordinances that favor them, for example;

Rewards for passive solar design in the Building Code of Australia

The Building Code of Australia (BCA) 5 star benchmark substantially rewards passive solar design and makes it difficult for non-passive solar designs to be approved in Perth.

Hi Jason,

Our home, like so many, is oriented east-west and, regrettably, the south side is heavily shaded and a disproportionate amount of glass faces due north (perfect for Australia, but not so good in these parts) -- you would be hard pressed to find a home more ill-suited for passive solar. In cases like this, your only option is to insulate and air seal to the best of your abilities and to select a heating system (or systems) that utilize one or more low cost fuel sources.

If my numbers are more or less correct, our average heat loss is about 0.17 kW per degree C, when temperatures fall below 15C/59F (above 15C, various internal heat gains are normally sufficient to maintain a comfortable room temperature). Last year, we used roughly 4,100 kWh of electricity and perhaps an additional 250 litres of fuel oil for space heating purposes; this winter, with the addition of a second ductless heat pump, our electricity consumption will likely top 5,000 kWh but, with that, we will have effectively eliminated the last of our fuel oil requirements. I should note that this is a 40-year old, 230 m2/2,500 ft2 Cape Cod with an un-insulated concrete floor and partly slab on grade construction, and that our heating degree days number 4,367C/7,860F; we had to literally tear this entire house to the bare walls to accomplish this level of performance, but it was well worth the effort.


Good website for degree day calculation :

Thanks, orbit500. I've put this web resource to good use (weather station: CYHZ) and have recommended it to a number of my friends. My only wish is that we could go back more than three years, but that's a minor quibble.

For Canadians, weather data as far back as 1840 is available at:


ONce a house is built that is poorly situated, there really isn't anything that can be done to fix it, is there? Or are there some aspects of solar design that can be used in renovations?

We will cover this topic in Part 4 of the series.

There are some passive solar renovation (or add-on) approaches that can be used; the overall results are highly situation dependent. Active solar measures can also be taken, and are more likely to provide a greater percentage of solar heat.

I would imagine with such houses you'd be more or less stuck with a passivehaus-style retrofit, no? Or, bringing in as much heat as you can by other means, such as heat pumps, solar, etc., I'd imagine.

Thanks for this piece. It's a subject rarely touched on here except in passing, but perhaps key to sustainable futures.

Would I be right in assuming Part IV might deal with types of structures, e.g., straw bale, cob, passivehause, envelope (enertia is the only example I know of), rammed earth, Earthships, etc.? Is there a part on sustainable building coming?


It would be easy to write 100 pages on this topic, and still not adequately cover all of the items you've mentioned. Most of the latter list are building materials, which falls under energy efficient building practices, and there has been discussion about such an article series. And Passivhaus will likely be covered in this series by another guest author.

It would be easy to write 100 pages on this topic, and still not adequately cover all of the items you've mentioned.

Agreed. I suggested elsewhere that you list the coming topics so others might consider posting on topics TOD staff/guests aren't planning to cover.


In rural areas with lax siting rules the biggest windows tend to face the best views, not the equator. Re climate change I think what may happen
- year round cloud cover will increase
- expect unseasonal weather anytime.
This may mean less winter insolation and the need for quicker temperature adjustments.

The house design shown doesn't appear to allow much convective cooling if I understand it right. BTW I got the lowest rating of 3 on the BoM June insolation map.

The house design shown doesn't appear to allow much convective cooling

Yes, it is simplified for basic illustrative purposes. We'll touch on solar cooling approaches later in the series.

Will you also talk about the use of deciduous vs evergreen shade trees, or similar shading with trellis and vines, for heat control?

My zone is heating-degree-day dominant, but the sun is blazing in the summer and my S and W bricks heat up to over 130F. The A/C runs will into the night from this unwelcome thermal store. My parents over came this issue with a number of trees and some grape vines -- not a look many people would want, but quite effective.

Can window shades, including roll-downs (if you can handle the expense) help with adverse summer insolation and winter overnight heat loss?

Will you also talk about the use of deciduous vs evergreen shade trees, or similar shading with trellis and vines, for heat control?

Yes, as far as it relates to solar input. Micro-climate landscaping is an oft-overlooked area.

Can window shades, including roll-downs (if you can handle the expense) help with adverse summer insolation and winter overnight heat loss?

Yes, that will be covered in Part 3, under Controls. I use insulated window shades myself.

There is much written about passive solar heating on the Internet but very little about active solar heating. Everything I do find points to a simplicity vs complexity argument as in inexpensive versus expensive and liable to break.

Does anyone envision active coming back into vogue?

Has anyone modeled their passive home using computer programs and several years of hourly insolation, temperature, and wind data? What programs have you all used? how close was the program to reality?


I'm working on a number of Active additions to my house, including Hot Air Box Collectors on the Roof and South Faces, Window Quilts Inside (active in that you need to actively open and close them 2x daily), and have an inclination to put insulated shutters on windows outside which could be set to open/close automatically, on timers, etc.. (and be overridden manually, as desired.)

I've also assembled many of the parts for 'active refrigeration' with a heat exchanger outside, a 'coolth' storage tank and an exchanger inside the fridge. .. And active Solar Lighting, which uses one tracked mirror to send a beam of sun down a chimneyshaft, to be dipped into by mirrors adjoining various rooms.

Too many projects.. but I think that even a very small amount of active assistance can be a huge gain for many RE applications. Thermostat and Fan, Light Sensor and Motor Switch, Temp Sensor ... etc. But even for more complex control, I would probably let the brains be more of a 'Stamp Computer' or Microcontroller .>>($50/$150) basic setup, which draws milliwatts.. instead of a full time dedicated PC.

Happy to spitball anything you're thinking about. (Here, or email at my ID page)

I live in Australia and it's amazing how few people here, including real estate agents, have heard of the concept of solar passive design. I'm in the market to buy a house at the moment, and I spend my time trawling through listings of houses for sale, searching in vain for homes that have significant solar orientation. Maybe 1 in 100 have solar passive potential, and then it's only by chance. Typically I find houses on large blocks, up to 1 acre with infinite possibilities for positioning a house, facing due west or any direction but towards the sun. And yet I knew about solar passive design in 1980, and I picked it up from the general media. So what excuse do these builders and architects have other than incredible stupidity?

Informed buyers will be the impetus for changing the market. I had to build my own house, as I found none on the market that would be suitable.

In the US, it has traditionally been cheaper to build than to buy, but harder to get financed. Given the subject matter of this thread, perhaps you should consider a renewable building such as straw bale, cob, etc. You might save a lot of money by going to a natural building workshop or two then building yourself. These designs are simple enough that you could DIY from top to bottom for the basic structure. Electrical and plumbing or any specialized systems, perhaps not.

The beauty of these designs is, if done correctly, they virtually eliminate the need for heating and cooling. Or so they say. If you've the money, you could go with the expensive envelope style that Enertia has.

As a matter of principle with an eye toward sustainability, I am not a big fan of passivehaus because the building itself is typically not renewable. If you build with natural and recycled materials you are helping the global community move closer to sustainability.


Why are Passivhaus and sustainable materials mutually exclusive? Could you explain this a little more?

Other than lots of glass, why does a Passivhaus have to use non-sustainable materials?

Why are Passivhaus and sustainable materials mutually exclusive?

I didn't say they are. I said "typically." But building a straw bale to passivhaus standards is defeating the purpose and is redundant. Maybe you'd do it with a solid wood house, like the Enertia homes, but are all-wood homes sustainable for billions of people? Can we grow pine that fast?

Other than lots of glass, why does a Passivhaus have to use non-sustainable materials?

They don't. But can you show me many/any that are built sustainably? The passivhaus concept seems to be a greenwash to an extent. It's used by people with an eye toward ecology rather than energy per se, let alone sustainability.

I think passivhaus is an excellent answer for owners/renters of existing structures. Since my long term eye is so focused on sustainability, for new buildings I pretty much dismiss those ideas that aren't inherently sustainable.

Put another way, I'm not sure we can go on letting "greens" feel good for saving energy, but not living sustainably. We can't let the Gaian types get away with completely renewable schemes that are not reproducible on massive scales. Peakists can't be lauded for saving energy in their passivhaus built of materials that are depleting. Etc.

Energy, sustainability, ecology. All considered at all times.

I see no other way.


Good luck getting a certificate of occupancy with that.

Never forget, government is at least twice as stupid as the dumbest person. Building codes are rarely updated and at current totally worship at the altar of present safety.

Good luck getting a certificate of occupancy with that.

One should choose their location wisely. If such a location can only be found where such restrictions exist, then they can kiss my Constitutionally protected arse.

You are aware there are straw bale and cob homes all over the place, though, right?


I live in Canada and I have been trying to weigh out two scenarios. (A) - try to improve the energy efficiency of my own house, which does not have the orientation, superinsulation, thermal mass, windows, radiant floor heating, wood heating stove, that I now know that I wish I had. (B) - Just start from scratch and build a new house the way I want. My search for buying a used house with passive solar potential has been like finding a needle in a haystack. Other factors for the house that are significant to me - distance to work for both myself and my spouse, good neighbors, topsoil. I started thinking about this around June of 2007.

Hi june,

There are times when I wish I had bought a new R2000 home and avoided all of the things you mentioned (generally, after coughing up half a lung of plaster dust). But at the end of the day, I wanted to live in an older, established neighbourhood with lots of mature trees and within easy walking distance of all the places I need to go; e.g., the library is a five minute walk and my bank, grocery store and just about everything else is under ten. I'm now doing more field work, so I'm using my vehicle more frequently, but prior to this it would sit in the garage unused, to the point that my battery went dead so frequently it would no longer hold a charge. If I were to build new, it would likely mean moving further outside the city which, in turn, would only foster a greater dependency on my car or, alternatively, tearing down an existing structure which would be a tremendous waste in itself.

Renovating a home can be messy, disruptive and seemingly endless work and it can put any relationship under enormous stress; it's also difficult to achieve the same level of technical performance. I wouldn't advise going this route unless you know what you're getting into but, in this case, the home and neighbourhood were the deciding factors.


"But at the end of the day, I wanted to live in an older, established neighbourhood with lots of mature trees and within easy walking distance of all the places I need to go; e.g., the library is a five minute walk and my bank, grocery store and just about everything else is under ten. I'm now doing more field work, so I'm using my vehicle more frequently, but prior to this it would sit in the garage unused, to the point that my battery went dead so frequently it would no longer hold a charge. If I were to build new, it would likely mean moving further outside the city which, in turn, would only foster a greater dependency on my car or, alternatively, tearing down an existing structure which would be a tremendous waste in itself."

We are similary situated - these are KEY REASONS why I feel that a large portion of a series like this should be devoted to retrofitting existing homes. New construction would involve loans (at a time when credit is tight & unlikely to improve anytime soon), use of more resources, living further from established areas, potential longer commutes... etc, etc. Would there even be a net energy gain from building new construction, properly situated and designed, when you factor in use of additional resources and longer commutes?


Yes, but depends. Some examples can be found at Dancing Rabbit EcoVillage. The policy there is to build with renewable and/or recycled materials only. (As far as I know that doesn't extend to, for example, their compost toilets.)

Now, how much material is there in the form of unused, old, torn down stuff? Don't know. How many older buildings get torn down each year? How many abandoned? Again, don't know. However, using earth materials - clay, straw, hemp, etc., surely is better than the usual. And, anybody, not just those with prior construction experience can build the basic structure.


Mamba,some of the mining towns which were built during the 60s and 70s in Australia's tropical far North used proper solar orientation.Weipa is a good example with curving streets,lots of trees but all houses line up East - West.Houses high set to catch a breeze, floor to ceiling louvres and wide eaves so that windows can be left open during rain.
These types of houses were also built in South and Central QLD at this time.These days there are mega burbs full of low set brick veneer monstrosities,some with no eaves(the Tuscan style) and oriented toward the street,whichever direction it runs.
Expensive environmental disasters,monuments to stupidity,fashion and developer/builder greed.

Maybe Nate Hagens can shed some light on why the lessons and solutions of the past are forgotten.

My family built a house ( in australia about) 15 years ago, taking into account passive solar design. Since then i've been surprised several times by the difference in temperature of our house, which doesn't have aircon, compared to other houses, which have to have aircon in order to survive in summer.

I'm surprised that more houses aren't built using passive solar principles, as all it takes is to point the narrowest wall of the house west, with small windows on that walls, and big enough eves to block the sun in the summer.

two items which arn't mentioned here here are roof insulation - we added that to our house a few years after it was built and in hindsight should of done it sooner, and the role of airflow in cooling a house - air vents at the top of the roof to draw out the hot air which can accumulate there and indirectly heat the house would make a big difference. -- this last item only works to keep a house from raising above the ambient temperature, and some of what is written above is about building to keep warm in cooler climates, where you would want to not let any heat out at all, and a mechanism to move heat from the roof space to the house w/o allowing the reverse to occur would be useful.

My assessment has been that solar space and water heating is very complimentary with nuclear base power. Even if solar heating meant that daytime water and space heat were covered by solar rather than electrical sources, then there would be a better balance between day and night time power demands, hence less demand for day time only peak power. Since conventional nuclear power works best as a base power source, winter solar passive heating is a better and probably more economical alternative to supplying winter peak demands from solar sources.

I'd suggest you need to cover walls and roof, and heat transmission/lag through them. In terms of keeping cool on a summers day, let alone keeping warm on a winters - these are the factors that really dominate.

Will be an interesting series, I hope to find something new.

The design of the roof (short side to the south, long side to the north) is really what is most common with the houses built in the last 2-3 years in Austria, but I think it is a very poor choice. Why?

Because you lose lots of space where you could put on e.g. vacuum tube solar pipes (quality ones like

Another good "official EU" detailed irradiation map / online calculation program:

I'm looking at building a (mostly) Passive House with straw bale and have been stunned at just how little solar heat one can get from the sun. As my basis I use the ASHRAE tables in The Passive Solar House by Kachadoria. I'm partial to his solar slab as well as combining it with a good 3' of insulated sand underneath that is heated with waste heat (summer) from solar hot water heaters. Ignoring that active solar heat here are two homes (existing early 90's vintage and proposed). Existing is 1500 sq-ft sprawling split (semi-detached) vs 2-story 1200 sq-ft with 150 sq-ft of south glass (72% of wall area) in cloudy southern Ontario (not sunny VT or CO).

Area R-vale, BTU/hr/F
Walls 21, 90 40, 24
Ceiling 30, 37 60, 10
Floor slab 3?, 153 15, 31
Doors 5, 8 5, 15
Infiltration -, 86 -, 52
Windows 2, 68 5, 30
Total 444 161
Thou BTU/day 580 237

So a better insulated home reduces my heating load by half.
Going to the ASHRAE tables gives 10 kBTU/day in Jan and 8.4 in Dec.

As per Kachadorian - double glazed windows (as opposed to triple as above) would allow more heat gain and when combined with insulating shutters - the house, by my calcs, would peak at about 20% of it's heating need via solar contrib.

I refuse to add in electrical heat gain in the house. Often the people doing this have energy pigs inhabiting their green-washed castles. My family is around 7 kWh/day in the winter and if we go without a furnace that'll knock around 2 kWh/day off, and if we use heat recovery from the fridge/freezer compressors (likely enough heat to heat our water) then that knocks off another 1kWh/day. However, I see the future as not having a fridge or freezer as one has a free fridge/freezer (outside) in the winter. A cold cellar would be part of the home design. Our current - electrical energy thirsty lifestyle (7 kWh/day winter) includes cooking, clothes drying and mostly standard house. It's N, W, E facing and so passive solar is out of the question - no roof alignment and no side facing south at all. The wierd thing about our Co-Housing group is that most of us have homes with none, nada, kein south facing walls! We all want it - but then we see houses with south exposure and people have papered over the windows with aluminum foil or have them shaded ...

I always wondered what the techno-worshiping Amory Lovins was smoking - until I saw that he included massive amounts of waste electrical heat as contributing towards building heat. But he did, apparently do a heat recovery from compressors and I applaud that.

I'm looking at building a (mostly) Passive House with straw bale

I'm confused. While straw bale homes have a high R factor for the walls, they are also designed to "breath." Isn't this contradictory?


Excellent question. When houses are said to 'breathe', this refers to their ability to allow moisture to egress the shell, keeping the insulation dry and effective. I believe your concern is with 'infiltration' of air (like on a windy winter day), which refers to the draftiness of a shell, undesirable levels of which rob a house of energy savings. These are two similar seeming but different subjects.
Strawbale Building FAQ

Way cool (says he sitting in a conventional house @ 40C @ 9 pm ). I'm looking forward to this series
big time. Wife's gonna raise eyebrows when I take to the house with a chainsaw though. Thanks Will.

Could remodel like my father did. He wanted to add a basement extension under the back porch/woodshed of their farmhouse (1920's frame). To make the joining opening, he chipped away at the existing basement wall (concrete facing on heavy stone structure) a long time and made little progress. All four of us kids who would have typically gotten such an assignment had long left home by that time. Being experienced with explosives, he asked mom if she would allow him to blast the opening, she refused. So he set the explosives, lit the fuse, then went upstairs and told mom "You'd better come outside now." Mom told me it actually blew open a perfect opening as required, but all her dishes were in a recessed cabinet directly above. The explosives opened all the cabinet doors, lifted all the dishes out and set them neatly onto the floor in front. Not a thing broken.

Fortunately mom was quite forgiving. I told the story at their 60th wedding aniversary, got a good laugh.

An aside on thermal mass.

When I moved back to my farm in the country I build ,over three years, a loghouse of western red cedar. There was a lack of building and Jim Barna Log Homes made us an offer we couldn't refuse. A log package of WRC for the same price as common pine.

So I built totally alone and by myself a 4500 sq. ft. (under roof and full poured 12 " concrete basement) log house.Not a cabin.

I initially heated it with an old Amana split-union heat pump(air).

It barely did the job so I put my old triple-walled large wood heater in the great room and it alone would heat the entire house if I fed it good seasoned oak or hickory.

Along the way I learned some important lessons about thermal mass as it applies to log homes.

The heat inside is slowly stored within the thermal mass of the logs. That makes it a very even heat and if the stove goes out the logs return the heat stored within. This is very important. It means I used no heat or cooling at all for most of the year as the logs both outside and inside worked with the passive solar(nothing created as this post indicates)...

I later replaced the old Amana with a Geo-Thermal 4 ton heat pump. Florida brand and ran it off my own well. Pumped the output to the holler that was near the house where it sank back into the aquifer.

My electric bills were very reasonable. The upstairs was heated by the rising heat and so we slept upstairs in the winter. The home was pretty much open architecture with cathedral ceiling in some areas.

In the summer we slept downstairs or could have gone to the basement where it was always 65 or so degrees and hardly varied.

I had a large sunporch added with screen for additonal usage on hot days.

The benefit of good logs , such as WRC are very worthwhile. The thermal mass if used correctly is amazing.

I built two foot overhangs and used all Anderson windows including the skylights and 8 ft sliding glass door.

It was too large for me after my wife decided to live back in the suburbs so I moved back to my previous living quarters on the farm. The loghouse is empty now but some day I might return. Not sure.

I prefer my crowded, unplanned, helter-skelter, shop alongside , finished pole barn and heat it with a lot smaller amount of wood.
So far a tad less than one cord used.

WRC,western red cedar is now hard to obtain. Others are very expensive and pine is IMO not a good choice.

Airdale-my experiences,yours may differ..but here in W.Ky the temp averages between the seasons are perfect IMO. Not too cold,not too hot. Not that I suggest anyone moving here. I like it sparse and neighbors not toooo close.

BTW when you build a house of logs..When you lay the logs? Then you have just finished the outside,no siding required or sheating, and you have also just finished the inside walls as well. No wallboard and no batt insulation or insulation of any kind.

Of course you might need to put finish of some protective kind on the outside BUT if you have sufficient overhangs and no rain touches the logs then you rarely need a finish but the sun on the south side can weather the logs. The best solution is a wrap-around porch with large overhangs then the logs will last centuries. No deterioration if you have WRC. Pine and other is different as the wood bees will totally destroy it over time.

So you save tremendously in other costs.

I did put finish on mine but WRC will silver out to a very nice rustic finish if left alone. Pine will just get splotchy due to ultraviolet staining.

Another factor is they are rather fireproof and withstand small, perhaps quite large, earth quakes. Being on the New Madrid fault line I have had quite a few very large tremors and not a thing fell or moved. Some epicenters have been with 15 or 20 miles.

One I heard coming across the fields and woods.Then heard it as it passed on to the southeast...making lots of noise as it went.In that one my buddies older frame house had some broken log sleepers under it split and crack wide open.


I was surprised to find a link leading to a researchpaper describing a project to build passive solar houses in my hometown in the Netherlands, especially as I had never heard of them all my life there! Many new buildings ignore passive/active solar possibilities.

Goes to show the short memories people have. They tend to forget things that aren't absolutely necessary any more.

Similarly: most houses in rural Wales up to 1950's(?) were built south-facing, with larger windows south than north, but after that orientation became random, as if people forgot such a usefull technology completely.
(And I'm sitting here in my house lamenting it's lack of insulation..damn houses built in the 50s)

In 1996 we built a home designed by this company:
It's great. 2400 square ft and we burn 2 cords of wood - no backup - and we live in Vermont. In February on a cold sunny day (down to maybe 20F) we don't need to make a fire (till the sun goes down. It's relatively cool in the summer because it was properly designed with overhang.

Basically it's r36 on six sides (insulation and vapor barrier against the ground), an air intake in the center of the open layout (2 1/2) stories) which takes the hot air that rises and draws it down to the 10" thermal mass below, then up through vents around the house.

However... we have had to make several compromises because we are off grid. I imagine it would be even more efficient without these changes. We hardly ever use the fan mentioned above, except in the fall & spring, b/c it draws too much power. The house would be tighter except that our water heater (aquastar instantaneous) is vented through the roof. This is OK for us because we use propane for cooking which they didn't recommend because the house would be so tight. No way we could do electric being off grid.

Even with the wood stove the humidity is a very comfortable 70%.

I think the only thing I would do differently would be to have a wood stove that would draw air from outside.

We live in a AAE house also. I have no complaints. Works great! We have a grid tie PV system and solar hot water. Between the passive heat gain of the house, the PV system and solar hot water we supply all our energy needs.
AAE makes a great house.

Are you on a solid slab?

Our Passive Saltbox in Western Maine (1980) had a 'cool tube' intake for fresh air supply and to fight infiltration of winter air through cracks.. air supply was under the frostline long enough to come in at 40degreesF plus.

Some designers worry about mold in the condensation in these in the summer though. Ours was perf'd 4" drain pipe, and I never heard of any problems.


Yes, a 1 foot thick concrete slab. The concrete slab is the heat storage and it's insulated from the ground by 4 inches of celotex rigid insulation. No fresh air supply except for opening the windows.

Sun warmed air is brought down from the interior vaulted ceilings and distributed thru ductwork in the slab.


Yeah, that's what it sounded like.

After the ground thaws next year, you might look into getting an air supply like this going.. Ours was a system called a 'cool tube', tho' I have seen precious little out there on the web about them, aside from the mention of potential mold from summertime condensation.. (which would scare anyone off, I'm sure)

Ours was tied into the perimeter drainage pipes (french drain?) outside the foundation, and their entry point into the house was under a raised kitchen floor near much of the plumbing, where it was designed to keep the pipes above freezing in addition to the other benefits.

In a house with combustion heat and cooking and tight envelope, you not only have the O2 levels to consider, but the negative pressure created by the exhausts, which will draw on any cracks/voids that do exists, bringing in the cold air, but which in a really tight enclosure will be what helps make a natural suction to run a cool-tube like this without any fans, etc. (A small fan might be helpful just the same..)

Without going through the slab, a variation might be to make a root-cellar next to the building which can double as a transfer point from a pipe-air/input string to a final above-ground insulated delivery tube that enters a wall of the house. The root-cellar would provide an access-point in case one needed to occasionally check the condition of the run for drainage, cleanout, etc.

The cool tube in our Stoneham House was probably closed up by the current owners, who have nonetheless been very happy with the Passive Solar, even though they replaced a lot of the southern glass with much smaller windows..(!!!) they have told us it's still the cheapest home to heat they have ever been in, and they moved to Maine from New Jersey! It has a fine Russian Fireplace at the center, tho' these folks have added Propane heat, I hear. I think we'll have to draw up some historical notes to go to them and offer to future owners, for those who would take advantage of systems that most people have no idea how to run..


I've seen people with cool tubes that fashioned cleaners for them. 2 lengths of cable and a bleach-soaked bundle of cloth. 1 cable was already in the tube and the cloth was tied to the end, as was the other cable. A slow steady pull coated the tube with bleach, and drew the next cable into the tube ready for the next cleaning. I had considered cool tubes myself, but was hesitant due to the mold concerns in out hot, humid local climate. The trick above should alleviate those concerns, though I'm not sure with what frequency the bleaching takes place.


It sounds like the information about moisture you are asking for can be found using a psychometric chart. This gives the relationships between air temperature, moisture and relative humidity.

A geothermal air tube will deliver air near average ground temperature, which can be found on tables like those of well water temperature. Of course, if already existing, just us a thermometer. If the outside air saturation temperature (found by knowing the relative humidity and temperature) is higher than ground temperature, moisture will condense in the tube. Therefore a proper design should provide for the moisture to drain somewhere other than into the house, or collect in a low spot and block the tube.

If outside temperature is lower than ground temperature, heating of the air will occur and this will lower the relative humidity; therefore, I would not expect any humidity problems with an air tube during winter in cold climates.

Geothermal make up air tubes make good sense. Ideally they are part of the original design so slope, drainage and radon issues can be properly addressed.

Thanks for the points!

It was always considered that we just not run it in the summer, yet the cool draft was a great relief even in a modestly balmy White Mountains summer day. Ours was built with the foundation, and were very well drained, so our mold concerns were minimal.. but having a reliable testing procedure would be a sensible backup plan.

Correction: psychrometric chart

Unfortunately, IMHO we have a massive surplus of both residential housing and commercial buildings in the US, and will continue to have a surplus for a long time to come.

The US is going to become a much poorer country. Among other things, this means that the square feet per person is going to have to shrink. Households are going to have to take in relatives or lodgers, or add accessory apartments in the attic or cellar or garage, or remodel to turn single family homes into duplexes. The McMansions in the remote suburbs, far from places of employment, are going to become increasingly vacant; when a sufficient percentage of the total housing stock in a suburb becomes vacant, the suburban government will go bankrupt, public services will stop, and the remaining residents will have no choice but to pack up and leave. Thus, it is going to be a very long time before there is much new housing construction again, other than a little bit of infill and tear-down/replacements in prime locations.

Since the US had about 7 times the amount of retail space compared to more sane countries like Sweden, we can expect massive vacancies of commercial space as well as we see massive store closures and retailers go out of business. It will take us a long time to figure out how to repurpose all that space. Thus, it will be a long time before we start seeing much new commercial construction in the US, either.

Thus, the name of the game for the next couple of decades, at least, is going to be remodeling and retrofitting existing buildings to make them more energy efficient and to repurpose them for the real needs of this new, declining economy.

While passive solar heat makes wonderful sense for new construction, unfortunately there is going to be very little of that. Retrofitting existing buildings to utilize passive solar is a much more difficult challenge. Sunspaces can be added to the south walls of quite a few buildings, and that might be the best bet. There is one of the few growth industries that we are likely to see, and a good opportunity for a lot of those newly unemployed construction workers.

I suppose that for a lot of buildings one could just put more windows into south-facing walls (and maybe taking out and closing in some north-facing windows). There are also cheap and easy things one could do to add some thermal mass that could be heated by those south-facing windows. Adding awnings on southern exposures is also feasible.

I'm not sure what else is feasible for a wide range of existing structures. In many cases, the additon of active solar heating systems starts to look easier and less expensive.

I believe that 98% of existing housing is obsolete compared to a properly designed massive thermal type house.

I agree that there are way too many conventional houses. I refused to buy one and built my own, using techniques like those discussed here.

Unfortunately, home buyers, builders and real estate people know nothing about this kind of construction.

I believe that 98% of existing housing is obsolete compared to a properly designed massive thermal type house.

I agree that there are way too many conventional houses. I refused to buy one and built my own, using techniques like those discussed here.

Unfortunately, home buyers, builders and real estate people know nothing about this kind of construction.

Because they know nothing, 98% of new construction continues to be obsolete even as it is built. We would be much better off to just stop building anything new for a while, and wait until the reality of our energy future really sinks in and people are ready to start dealing with it seriously. Maybe it is just as well that the economy is doing this for us, as otherwise we would never stop building the wrong way.

I think that is an overreaction in the wrong direction. Google Green builders.. there are some in every state, I'm sure. And either Hire them, or give them some new competition.

We have a lot of people who need good work.. we have housing stock that needs to 'work smarter' .. Two problems with a common solution. I know you said NEW construction.. but that is part of the mix. We need more renovation than new construction, but both are part of the mix, and doing both will help to steadily bring our housing energy demand down.

Use recycled materials.. use strawbales and tamped earth and Trucktires.. but I think we need to get people to work, rebuild the building trade, and get right onto making our homes efficient. It's probably one of the most important ways to make people resilient to energy and financial shocks.


{EDIT : And build it to LAST! My home has 4x10" Floor joists, and probably 8x10" framing beams with shippers joints that have been sitting solid here for 158 years.. a good use of trees!)

I am aware of the green builders and they are doing a good job on new houses in the thousands. Meanwhile, the clueless "conventional" builders have been building same-o, same-o houses in the hundreds of thousands and millions.

Of course, builders have to build to a market, and the public doesn't know anything about construction.

My neighborhood association blocked use of a special cool roof color on my aluminum roof (this is a hot climate), and they didn't like the type of house I was building, but I had previous approval of AAC as the building material before the developer turned administration the association over to the neighborhood.

I had some very ugly meetings with the association, and almost ended up suing, especially since the association president's wife ran a business at home in violation of covenants.

So we have a long way to go in this country. Our best hope is getting a tougher building codes for energy efficiency and durability.
If advanced building materials were standard, the pricing would be equivalent to conventional construction and we would all enjoy the savings.

I'm sure Architecture 101 teaches concepts of house orientation and passive solar, but architects will design what their clients tell them to. Clients look at standard home plans, and not a cookie cutter plan I've seen says this house is designed to face North, South, East or West! It's the architects job to do deal with these issues; they know how to do it correctly!

I would like to see a small 800 - 1200 sq ft dweling , simple ... single story .

In my area and others cooling is more of a energy drain than heating , night sky needs to be included in the equation as that is where summer cooling is going to come from.

A south wall such as this may be the best ...

although Laren Corie ... feels the storage should be in the ceiling

Exterior only insulation like seems to have the best rating from

It needs to be affordable and not something only movie stars can build ... I have a cleared space and ready to build

More detailed tables of sun hours for many Canadian municipalities can be found by entering the community name at

My previous house was a passive solar design to which I later added a small vertical wall active solar panel on the south wall. The roof design also allowed for the addition of hot water solar and the possibility of PV.

The house was 1500 sq.ft, with no hallways as wasted space. Three bedrooms, 2 baths. The living area (great room) opened to a dining area and a bacony from the master bedroom. It also incorporated a Heatilator fireplace (outside air supply, active stainless steel heat exchanger with fans).

The key to this house was it's orientation (no north facing windows), it's open design and the extremely high insulation values in the walls, celing and floor (R-38+ ceilings, R-24+ walls and floors. It was a crawl-space design and the builder (who built these as passive solar homes) took particular care to insulate corners, seal windoes, etc. Even the upper crawlspace access was weatherstripped and had an R-38 batting attached to it. Unfortunately, triple paned windows were backlogged well beyond out contruction complee date so we went with aluminum, foam-filled double panes.

As for site orientation, the main windows faced due couth. The front door access faced north but was able to accomodate a small vestibule/air lock for the winter. On the north side of the house we had pine trees to cut the north and northwest winds. On the southwest corner and western facing side, we had white oaks (approximately 75-85 years old)that provided fine shading for the late afternoon in summer and minimal shading in the winter. The long overhangs of the roof obviated the need for gutters.

Our power bills (used a heat pump to heat and cool as necessary) were minimal and the fact that I used the residential time of use rate gave me a real break since I was willing to put such things as the hot water heater on a timer.

My current house is not passive solar design but has many of the same features incorporated that the one that was intentionally designed with passive solar in mind. High insulation values, no north facing windows, good windows.

Good start to the series Nate. I still have my dusty old book collection from the 1970's, passive solar, solar greenhouses, movable insulation, post and beam passive solar houses, etc., and this makes me think of the old days.

I found out in those days that if you wanted it done, you had to do it yourself, no local builders would even talk to you about passive solar. Sadly just when we got a crop of young builders willing to discuss it, the oil price collapses and they all went into "fast building mode" like the big boys to make fast money.

One thing I would mention to folks concerning efficient cheap housing...basement houses. I know, they have a "stigma", but I have friends who built them in the 1970's and the lifetime reduction in energy use has been fantastic to this date.

If you can't go with basement houses, whatever you do, find something to cover that north wall. Berming along that side is good, but I have seen some great designs with the garage for the car placed along the north wall, and that alone has been a huge improvement in any area affected by prevailing north winds (which is pretty much anywhere north of Atlanta!) Fascinating stuff, we could get natural gas consumption in the U.S. down to a trickle if we could get passive solar and solar hot water included as norms in most housing.


In looking at some of the mulching/digester systems people have developed, I was wondering if it made sense to build a really Stout and Sealed north wall and use it to buttress a mulch pile that provides heat, Nat Gas, and ultimately rich soil.

The old and oft/posted article about Jean Pain's multi-productive woodchip pile seems like it would be helpful to have at least one side holding its heat in, helping both the digestion and the home. Of course, north of that north pile could be another restraining wall against which you are piling up the dry chippings that will replace the working mulch after it's 18months are up. This doubly insulates the working mass..

The hot water pipes that run through this composting pile are now adjacent to your house, and so do not lose any heat traveling from A to B, and you can run the Gas Lines off to whatever cleaning/storage you've got, but probably away from the building.


I've been designing passive solar homes for about 30 years, mostly in the pacific nw but pretty much every climate in the US. I understand thermal mass will be considered in a future post but I wanted to weigh in on it now since so many of the comments are about thermal mass. I typically use a convective air slab for mass most of the time which is a concrete slab with hollow concrete blocks laid under it with their voids aligned north/south and linked at the ends with continuous east/west channels. Vents connect this underslab "plenum" with the conditioned space of the home permitting a natural convection loop of air to flow from the house living space through the slab. This greatly enhances the efficiency of the slab both for winter space heating and summer cooling. These homes can maintain a base temperature of around 60 degrees in winter and 70 to 75 degrees in summer without any imported energy. A simple duct outfitted with a thermostatically controlled duct fan running from the highest building location to the slabs north channel can give a "active" boost to the convection loop, assuring warm air gets into the slab regardless of whether conditions for a "natural convection loop are present or not. Warmed air from the sun, a back up furnace or wood stove is delivered reliable to every inch of the underslab plenum, even in an isolated room. BTW, a rule of thumb for mass for direct gain spaces is that you should have about 3-5 square feet (temperate to more extreme temperature range, respectively) of 4 inch thick concrete for each 1 square foot of south facing glazing. Isolated gain is more complicated. Mass walls are fine in climates with cold nights and warmer sunny days like the American High Deserts but they can be really problematic in climates where the daytime temperature never gets above 60 degrees and winter percent sunshine is low.


Sounds like a good design. I was thinking about something similar, but using hollow precast floor panels with tubular holes and a plenum at one end. Any thoughts on this method?

The precast panels should work ok to convey the air which still need to be aligned You don't say whether or not you plan to pour additional concrete over the precast floor panels??? You will need a channel to link the aligned panels at each end so there is a free flow of air and it will be more complicated to deal with air flow around footings I would think. You may want to check out my website www.sunsmarthomes for more info on the block method and you could contact me directly from there.

Thanks Tomahawk,

I looked at the photos on your website and understand how you do it. Interesting concept, and I will revisit it when I design my next house.

Hello Tomohawk,

Excellent information. Here's my concern, considering the use of concrete, concrete blocks, visqueen and styrofoam, how renewable is this? my question may seem petty at the micro level, but at the global level, do we run into supply constraints on any of this? What about CO2 for the concrete?

I had been planning to incorporate the envelope design in my own home when I build, and your solution seems like a nice combination of the envelope and radiant heating. It popped into my head that doing the same thing with cob/adobe might be a viable option. Many natural building methods use cob/adobe/rammed earth already. Laying in a layer of cob/adobe/rammed earth bricks would seem a natural substitution for those wanting energy savings and to build renewably. And it's DIY. Probably too time intensive for someone looking to make a profit.

Since the minimum temperatures you are getting are at 60F already, a simple solar air heater made of nothing more than aluminum cans and a box attached to this night easily bring the temperature up another ten degrees or more.


I'm torn about the water barrier... There's a lot of plastic in the world and, very long term, if we could - on a global scale - recycle all of it AND get our fossil fuel usage down to a bare minimum (i.e., not used for building, transportation, etc.) then the use of a little visqueen might be OK.

What are your thoughts with regard to cob/adobe bricks for this system?



You might want to look at ferrocement. It is basically wood frame clad in a metal mesh, like expanded metal, then plastered over with a cement mixture. The cavities are filled with pulped up newspaper, fireproofed with borax. The recycled newsprint is very good insulation.

This is extremely strong construction for the weight, and very durable. Lots of videos on

I'd definitely consider this in earthquake zones.

Thanks for the info, but I'm going to try to go all as renewable, recycled and local, if at all possible. Life has a way of making decisions for one, though, so I'll keep it in mind. Definitely will add it to the list of things to share with others.


for a basic design ... 20 x 60' rectangle .. 8' walls

Aperture ... long wall (8' x 60') pointing due south .. windows only on top half of south wall ,(hot air collectors on bottom half)

In my area a 4' removable overhang on south wall seems to work the best

Thanks for this post. I built a passive solar house in the desert area of Eastern Washington State in 1996 and have been very pleased with the results.

The long dimension of the rear of our house faces SSE ( a few degrees east of true south) and we have a sliding glass door and three windows on that side. The sliding glass door and three windows are double pane, argon filled with "E" coatings. The house is built with a slab floor insulated from the outside foundation walls with 4 inch foam blocks which acts as heat storage. The house has 6 inch walls, 30 inches of attic fill and all penetrations for wiring and cracks around windows and framing in the outside walls sealed with urethane foam to prevent infiltration. The walls have Tyvac on the outside and a full wall & ceiling poly vapor/ infiltration barrier on inside walls, All electrical boxes on the outside walls have foam inserts under the cover plates and the electrical box wiring holes are urethane foamed too. We get a lot of wind so infiltration control is very important.

Actually my first concern was over heating of the house and the extra load on the air conditioning due to summer sun since summer temperatures reach 110F ( winter of -10 F occasionally). Then the design quickly evolved into a passive solar heat too with a 3 foot wide louver extension straight out from the roof overhang ( "control" in the original post diagram) supported on a post and beam system. We extended one section out 12 feet to shade the patio.

The key to the louver design is to angle the louvers in the framing to an angle to maximize the sun entry at my latitude on November 21. The louvers were made from six each 1x4 cedar boards parallel to the roof. The design angle was skewed a month early from the winter solstice to skew the spring heat load to start to drop early. As Spring progresses and the sun angle rises the solar heat load drops steadily and in June there is zero sun entering the windows. This then provides solar heat in the winter months and reduces air conditioning load in summer.

I have found on a sunny day in winter there is enough solar heating that the gas furnace never comes on until we get below about 25 F.

It was probably not completely optimized by extensive calculations, but we are very happy with the sun coming about 14 feet into the Great Room today, and there is almost no sun into that room in mid summer. I hired a carpenter I knew who pre cut everything and installed it all for about $1400. I don't have much performance data, but the fact that our annual gas bill is less than our combined land line/ DSL internet annual phone bill makes heating a minor issue in our budget.

Coal into liquid and gas on a large scale appears on track to multi-million barrel per day levels by 2015.

South Africa's Sasol process and Indonesia project appear to be on track to an economic breakthrough.

Boosting the microbes in coal that naturally produce coal seam gas like the Marcellus and other gas in coal/shale formations could be huge to getting coal into methane/natural gas.

Coal into liquid and gas is cleaner than the solid coal, but still not as good as nuclear power or renewables. But at TOD people should know it is about money, profit and the insatiable need for liquid energy to power the machines. Coal is providing affordable answers at the needed scale. Hopefully other tech can step up for a better environment etc... but this would be the stopgap depending upon the timing of peak oil and the readiness of nuclear power and renewables at suitable cost and scale.

Did you mean to put this in Drumbeat? Seems unrelated to Passive Solar Homes..

I work for a small government department in New Zealand, and many years ago we used to do a bit of work on passive solar design. Thought it might be useful for anyone considering this stuff.

Part one of a manual on it is still available from our website:

And the much larger part 2 technical manual can be ordered on a CD, see the bottom of this page for details.




I am about to embark on doing a passive solar / green design for myself, wife and my sister. She is retiring and in one year and we will be working for another 10-12 I suppose.

This project is tabla rasa for us and the design will be driven by the energy concern and the small size we need. We haven't selected a site, but would lile one close to rail. We wouild like to build in southern Westchester, NY where I live (and work). I'm a licensed architect working for a high end marble and stone contractor (no more architecture clients)

I would like to bring a creative solar engineer on board. When is the right time? As we look for sites? After we find a site? After I have done the "schematic" designs? I am looking for advice and consultants. If you are interested in please contact me JSanderO at geee mail dot commmmmmmm.


This is good stuff going forward, but has no value in contemporary cities and suburbs. It took an enormous amount of energy to build this disaster, and the sunk cost is extreme - it will not be abandoned.

Example: go to some random working class home in say, Jersey City NJ, or some suburb of St Louis MO, or Toronto ON, and knock on the door and tell them "Tear down your house and build this kind of a Solar House."

Even if they agree with your position, they will say they can't afford it, as they are already up to their eyeballs on the mortgage for the house they already presently occupy.

So, while these kinds of designs will be needed to replace the present housing stock (when it finally collapses / rots away later this century) the most important thing that needs to happen is proper insulation and redesign of the interior spaces that already exist with an eye toward efficiency and comfort.

Later articles in this series will address renovations, both minor and major.

Several people have made the same point about existing homes, but you almost seem to be denying that homes are still being built. And, this discussion may implicitly seem to be about the US and Australia, we are really talking of global issues. It would do us all some good to keep this in mind.

I will, should I ever escape my current location, be building a home, almost certainly straw bale, cob, rammed earth... natural, at any rate.


With all due respect, I'd say it has all sorts of value to existing housing stock. It's a matter of looking at the principles involved and grabbing onto whichever ones your home might be able to use.

Certainly one of the central points of Passive Solar is being in a heavily insulated shell, since without it you can hold onto any of your heating income.

I'm in an 1850 Woodframe row house in a small city in Maine. I can't reorient the structure, but I can minimize my Northern losses, and maximize the South, where I do get fairly good sun. I will also have to add some active, but simple collectors to act as 'additional window space' .. Here is the design my first couple are based on. These are lightweight and fairly cheap to build, and would seem to be ideally suited to working class homes in the Bronx or Jersey City that have a bit of roofspace or southern wall exposure. These, and many other simple or semi-simple retrofits could use passive solar ideas to improve home performance. (Solar Hot air collectors ABOVE windows, built to look and work like Awnings, for example, would be heat in the winter and shade in the summer.. how many birds with that one stone? .. Insulated Exterior Window Shutters could perform many of the same tasks, and be informed by Passive Solar ideals..

Certainly it doesn't help ALL or maybe even MOST people.. but it could help an awful LOT of folks, so starting off your critique with that 'it Has NO Value' statement is both unhelpful and untrue.

BB's.. lots and lots of BB's (and fewer babies) is our only silver bullet.


I started designing passive (and later, active) solar structures in the late 70's on through the mid-90's, first in the US then in SW France, where I'm now living happily ever after. This kind of active discussion wouldn't have happened 20 years ago, or even 10, so thank you TOD.

A few thoughts:

1) You can make the design pretty complicated, and sometimes that's fun and exactly what you feel like doing. But it can be simple, as many of the posts here point to -- build a highly insulated shell, put in lots (but not too much :-) of good glazing to the south ± 20°, put in some shade, protect the north (berming is cool), put lots of thermal mass inside (concrete floors, masonry fireplaces INSIDE the shell are good places to start).

If you do all these things well, your major heat loss becomes ventilation losses (replacing warm moist stale inside air with cold outside air), so ABSOLUTELY use an air/air heat exchanger to keep inside air sweet. This uses electricity so it isn't 100% pure passive. I don't know what to do about that.

2) I did a lot of underfloor heating installation in the old days, and to anyone pouring a concrete slab (ubiquitous in Europe, slightly unusual in the US) I would still sing the praises of this absolute best way of delivering heat into an inhabited space. Yeah, I know we are talking here of passive houses that don't need any extra heat. But if budget permits, putting tubing into the slab can make sense. Even if it's not connected to any heat source (once the slab is poured it's too late!)

3) Calculating heat losses, surface/volume ratios, flow rates, etc. is about 14000 times easier using metric. Breaks my heart to read people talking in 31/83-inch air gaps and British Thermal Units. As we enter the brave new world, that's one heavy ball and chain to be carrying.

use an air/air heat exchanger to keep inside air sweet. This uses electricity so it isn't 100% pure passive. I don't know what to do about that.

You could always use DC fans running on a battery charged by a PV panel, with grid backup.  It wouldn't be passive but it would maintain your air quality even during a grid outage.

Calculating heat losses, surface/volume ratios, flow rates, etc. is about 14000 times easier using metric. Breaks my heart to read people talking in 31/83-inch air gaps and British Thermal Units.

As one who has written spreadsheets to do the conversion back and forth, it's not as difficult as it looks and it is probably required to be understood by e.g. building inspectors.

Is there a formula for sq ft of Aperature per cubic ft of dwelling .... Maybe Nick Pine knows ??

Anyway ... for 1200 sq ft of dwelling, I have 8 x 60' =480 sq ft of potential Aperature to gather solar thermal energy

The Nick Pine Simple Trombe Wall

or solar closet

is the best aperature for the money .. anyone know of a better one ?

I haven't seen sq ft of aperture to cu ft of dwelling, but I have seen;

A ‘rule of thumb’ for best performance is the exposed internal area of thermal mass in a room should be around 6 times the area of north facing glass with solar access. (note this is in Australia)

The metal frame is up ... how to figure aperature size

Your link doesn't show anything on either of my browsers, even after joining the group.

Where is the house?

How many square feet?

What kind of house? (ranch, colonial, etc)

What are the R-values and areas for the ceiling, walls, floor?

What are the R-values and areas for the east, west, and north windows?

How many ACH?

Any solar shading? If so, what?

Any thermal mass planned? If so, how much and how is it configured?

N. california ... 800 sq ft ... 20x40' ... ranch style shop / studio .. porch on 3 sides ... 4' removable shade on south side ... no windows on N or W sides

water storage in cabinet for thermal storage (4'x4' x 40')

You will first need to determine how much heat you will need based on the outside temperature, desired inside temperature, and the heat loss of each surface. This week's Passive Solar Design Part 2 article will cover all of this and help you understand how many hours/days of thermal moderation your 4'x4'x40 (41,000lbs) water storage will provide. But we can get you started on determining the heat loss now, so you'll be one step ahead.

Qloss = (Σ(UA)n + Cv)(ti - to)


    U = 1/R-value

    A = area (ft2)

    n = surfaces

    Cv = infiltration losses

    ti = indoor temperature

    to = outdoor temperature, normally the coldest in the 97.5 percentile (2.5% of the time is colder)

Just a quibble:

"The substitution of less viscous gases such as argon and krypton"

Argon has higher viscosity, not lower. Viscosity can be thought of as similar to "thickness", and reduces flow rates, so higher viscosity reduces convection.

Yes, originally I had it as "more viscous" and decided to change it to "less fluid" so that it would be more easily understood by more people, only I didn't finish the change. The overall effect later in the sentence is correct, though, so at least the point got across.