Reassessing Passive Solar Design Principles

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Reassessing Passive Solar Design Principles

Which design principles from the 1970s are worth retaining, and which should be discarded?

Posted on Oct 9 2015 by Martin Holladay

Everybody loves passive solar design. Back in the 1970s, “passive solar” was the essential first step for cold-climate builders. It was considered an approach with obvious advantages over complicated “active solar” schemes that required pumps, fans, and electronic controls.

While the definition of a “passive solar house” was well established by the 1980s, Wolfgang Feist muddied the waters in the 1990s when he decided to call his new superinsulation guidelines “the Passivhaus standard.” Ever since that fateful day, journalists and owner/builders have confused passive solar design principles with Feist’s superinsulation standard from Germany.

Rather than focusing on the confusion between passive solar design principles and the Passivhaus standard, however, I’d like to travel back in time to the 1970s, the heyday of the passive solar movement, to identify the original principles espoused by passive solar designers. Once these principles are identified, we'll examine how many of them have stood the test of time.

Here are the five bedrock principles of passive solar design for a cold climate:

  • The long axis of the house should be oriented in an east-west direction.
  • The rooms where people will spend most of their time should be located on the south side of the house, while utility rooms, bathrooms, closets, stairways, and hallways should be located on the north side of the house.
  • There should be lots of extra glazingWhen referring to windows or doors, the transparent or translucent layer that transmits light. High-performance glazing may include multiple layers of glass or plastic, low-e coatings, and low-conductivity gas fill. area on the south side of the house, and little or no glazing on the north side of the house.
  • The roof overhang on the south side of the house should be designed to shade the south windows during the summer solstice, but to allow the sun to shine through the south windows on the winter solstice.
  • The house should include extra interior thermal mass to soak up some of the solar heat gainIncrease in the amount of heat in a space, including heat transferred from outside (in the form of solar radiation) and heat generated within by people, lights, mechanical systems, and other sources. See heat loss. that comes through windows on a sunny day.

Solar vs. superinsulation

In October 2009, the Passive HouseA residential building construction standard requiring very low levels of air leakage, very high levels of insulation, and windows with a very low U-factor. Developed in the early 1990s by Bo Adamson and Wolfgang Feist, the standard is now promoted by the Passivhaus Institut in Darmstadt, Germany. To meet the standard, a home must have an infiltration rate no greater than 0.60 AC/H @ 50 pascals, a maximum annual heating energy use of 15 kWh per square meter (4,755 Btu per square foot), a maximum annual cooling energy use of 15 kWh per square meter (1.39 kWh per square foot), and maximum source energy use for all purposes of 120 kWh per square meter (11.1 kWh per square foot). The standard recommends, but does not require, a maximum design heating load of 10 W per square meter and windows with a maximum U-factor of 0.14. The Passivhaus standard was developed for buildings in central and northern Europe; efforts are underway to clarify the best techniques to achieve the standard for buildings in hot climates. Institute U.S. invited me to give a presentation at the Fourth Annual North American Passive House Conference in Urbana, Illinois. In that presentation, “The History of Superinsulation in North America,” I discussed the debate between “solar house” advocates and superinsulation advocates during the late 1970s and early 1980s. After Joe Lstiburek and John Straube saw my presentation online, I was invited to present it again at the 14th Annual Westford Symposium on Building Science (August 3, 2010).

Some of the information from that presentation was incorporated into a 2010 article, Solar Versus Superinsulation: A 30-Year-Old Debate.

Here's a quick summary of the relevant history: during the late 1970s and early 1980s, advocates of superinsulation raised questions about the validity of passive solar design principles. A debate ensued, and superinsulation won.

Although I’m quite familiar with the historic debate, and I side with the superinsulation crowd, certain aspects of the passive solar approach — an emphasis on careful solar orientation, a concern for proper roof overhangs on the south side of a house, and a preference for south-facing windows over north-facing windows — seem embedded in my DNA.

Lately, however, I’ve begun to wonder whether there is any technical justification for these recommendations. Do these design principles result in energy savings? Or am I just dragging around the stubborn legacy of my hippie past?

Forget the thermal mass

Some passive solar principles — especially the old belief in the near-magical effects of thermal mass — never made much sense to me. Thermal mass is expensive. Thermal mass complicates remodeling. Thermal mass makes a home unresponsive to sudden changes in the weather. By keeping a home cold when the occupants want to warm it up, or by keeping a home hot when the occupants want to cool it off, thermal mass is as likely to interfere with occupant comfort as it is is to contribute to energy savings.

For most cold-climate builders, the disadvantages of extra interior thermal mass outweigh any advantages. Even radiant floor designers, many of whom sang the praises of thermal mass in decades past, have mostly accepted the new consensus: low-mass floors are easier to control, and result in higher levels of occupant comfort, than high-mass floors. (For more on this issue, see All About Thermal Mass.)

This passive solar home in Lafayette, New Jersey was built in 1984. Photo credit:

How much south-facing glazing?

My faith in another passive solar principle — adding plenty of south-facing glazing — was first shaken by Gary Proskiw’s 2010 paper, “Identifying Affordable Net Zero Energy Housing Solutions.” (For a discussion of the report’s ramifications, see my GBA article, “Study Shows That Expensive Windows Yield Meager Energy Returns.”)

Briefly, here’s what Proskiw found:

  • South-facing windows are so expensive that the value of the heat gathered by the windows is too low to justify the cost of the windows.
  • Money that a builder might want to spend on extra south-facing windows would be better invested in other energy-saving measures.
  • The area of south-facing glazing “should be limited to that necessary to meet the functional and aesthetic needs of the building.”

It turns out that every extra square foot of glazing beyond what is needed “to meet the functional and aesthetic needs of the building” is money down the drain.

In a way, this advice is liberating: it compels the designer, secure in the knowledge that no technical or functional issues are at play, to think about aesthetic issues — and that’s almost always a good thing.

Proper orientation

What about orientation? According to conventional wisdom, the wise designer studies a site carefully, looking for a knoll with good southern exposure, and tries to align the long dimension of the house in an east-west direction.

Lately, building scientist Joe Lstiburek has delighted in puncturing this balloon. “I don’t think orientation matters anymore,” Lstiburek told me on the phone. “I see passive houses that are overheating in summer as well as winter — in Chicago! These houses need to reject the heat, not collect the heat.”

So where did the passive solar design principles come from? What’s changed since the 1970s?

Today’s houses are better insulated and less leaky

For one thing, passive solar buildings never worked all that well. Even back in the 1970s, they were cold on winter mornings and hot on sunny afternoons. But most solar enthusiasts were so excited by the idea of “free heat” that we accepted uncomfortable conditions as a necessary part of the brave new solar future we were all busy creating.

Second, today’s houses are better insulated and a lot more airtight than they used to be. That’s good, because they require less energy to heat and cool than homes built in the 1970s. However, recent improvements in insulation and air-sealing standards make homes with lots of south-facing glazing more susceptible to overheating — so it’s more important than ever to avoid excessive glazing area.

It’s also essential that we make the right decision when choosing between high-solar-gain glazing and low-solar-gain glazing. That decision has gotten trickier lately, especially since Proskiw's calculations have called into question the entire idea that south-facing windows are heat-collecting devices. Some designers (including Joe Lstiburek) have abandoned the idea of orientation-specific glazing specifications and now advise that all windows should have a low SHGCSolar heat gain coefficient. The fraction of solar gain admitted through a window, expressed as a number between 0 and 1..

Don’t do it

In a 2014 article titled “Zeroing In,” Lstiburek address passive solar design principles with his usual bluntness.

“Don’t bother with the passive solar,” Lstiburek wrote. “Your house will overheat in the winter. Yes, you heard that right. Even in Chicago. ... You should go with very, very low SHGCs, around 0.2, in your glazing. If this sounds familiar to those of you who are as old as me, it should. We were here in the late 1970s when ‘mass and glass’ took on ‘superinsulated.’ Superinsulated won. And superinsulated won with lousy windows compared to what we have today. What are you folks thinking? Today’s ‘ultra-efficient’ crushes the old ‘superinsulated,’ and you want to collect solar energy? Leave that to the PVPhotovoltaics. Generation of electricity directly from sunlight. A photovoltaic (PV) cell has no moving parts; electrons are energized by sunlight and result in current flow..”

Why passive solar doesn’t work very well

Four salient facts undermine the old premises of passive solar design:

  • In a well-designed house, the energy required for space heating represents a smaller percentage of a home’s energy budget than it did in the 1970s. In many low-energy homes, domestic hot water requires more energy than space heating. For more information on this concept, see It’s Not About Space Heating.
  • While large expanses of south-facing glass help heat up a home on a sunny day, the solar heat gain doesn’t come when heat is needed. Most of the time, a passive solar home has either too much or too little solar heat gain, so much of the solar heat gain is wasted.
  • At night and on cloudy days, large expanses of south-facing glass lose significantly more heat than an insulated wall.
  • These days, investing in a photovoltaic(PV) Generation of electricity directly from sunlight. A photovoltaic cell has no moving parts; electrons are energized by sunlight and result in current flow. array yields more useful energy than an investing in a south-facing window.

A new look at the old principles

So what kind of advice would I give a young designer contemplating the five passive solar principles listed at the beginning of this article?

The long axis of the house should be oriented in an east-west direction. I still have a sentimental attachment to this principle, even though I know it won’t save any energy. The reason I like to follow this principle — at least when the site allows it to be followed — is that it allows more rooms to get sun during the day. If you live in a cold climate, winter sun is cheerful. [P.S.: In Comment #6 below, Dana Dorsett makes an important point: While the passive solar principle favoring east-west orientation may be hard to defend from a space heating perspective, most new homes should, if possible, include a roof that is optimized for the installation of a PV array. An east-west orientation makes this possible.]

The rooms where people will spend most of their time should be located on the south side of the house, while utility rooms, bathrooms, closets, stairways, and hallways should be located on the north side of the house. It won’t save any energy, but this is still a good principle, for the same reasons that it makes sense to orient the long axis of a house in an east-west direction. However, if you live in a mixed climate or a hot climate where the sun is oppressive and shade is your friend, this principle can be ignored.

There should be lots of extra glazing area on the south side of the house, and little or no glazing on the north side of the house. This principle is overstated. If your site has a wonderful view to the north, of course you want to include north-facing windows — and you may want your living room or dining room to face north. Moreover, there is no reason to include extra glazing on the south — only what’s necessary (in Proskiw’s words) “to meet the functional and aesthetic needs of the building.”

That said, every house I have ever designed had more south glazing than north glazing — because sunshine is cheerful and I like sunny rooms. (Up to a point; watch out for glare. Many passive solar houses are so sunny on winter afternoons that the occupants all flee to the home's dark northern corners.)

The roof overhang on the south side of the house should be designed to shade the south windows during the summer solstice, but allow the sun to shine through the south windows on the winter solstice. Although there’s nothing wrong with this idea, it’s worth pointing out that it has always been impossible to design an overhang that will keep out the sun when it is unwanted and admit the sun when it is wanted. At best, the designer can come up with an overhang that kind-of, sort-of, almost works, but not quite. The sun is tricky. It follows the same path through the sky in March, when sun may be welcome, as it does in September, when it may be unwelcome. Moreover, at 10:00 a.m. and 2:00 p.m., it sneaks in sideways, at an angle, and stubbornly undermines the intent of the designer’s overhang.

So it’s OK to shrug your shoulders and accept imperfection in this department — especially if you take Lstiburek’s advice and just jump on the low-SHGC bandwagon.

The house should include extra interior thermal mass to soak up some of the solar heat gain that comes through windows on a sunny day. I’m happy to throw this principle out the window. However, if you live in a hot climate with high air conditioning bills, you may want to build a house with a lot of interior thermal mass. Just remember that many of the benefits of thermal mass can be achieved at a lower cost by installing extra insulation.

P.S.: Readers interested in reading a 1978 research paper on this topic may want to check out this report by Rob Dumont: Passive Solar Heating. Our thanks to Bronwyn Barry for sharing this document.

Martin Holladay’s previous blog: “Naming Building Parts is Tricky.”

Click here to follow Martin Holladay on Twitter.

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  1. Green Energy Times

Oct 9, 2015 9:26 AM ET

low-thermal mass sun-spaces
by Charlie Sullivan

Thanks for sorting through the issues, non-issues, myths, and truths in a balanced, rational, non-dogmatic way! This will be very useful for lots of people.

One idea that has recently been tossed around and tested as a different way to re-think passive solar design is a low-thermal-mass sunspace that is insulated from the house, but connected by operable vents, usually with fans (which I know aren't passive). The idea is to let the low-thermal-mass space get cold at night and on cloudy days, with it sealed off from the house. On sunny days it heats up quickly because of the low thermal mass, and you open the vents to bring the heat in the house. At the end of the day, most of the heat collected has been moved into the house, so you don't lose much stored energy by letting the sunspace cool off.

There's a fuzzy line between that idea and the idea of a simple flat plate solar air heater, the difference being that a low-thermal-mass sunspace is presumably big enough to sit in, during the limited number of hours that it's a comfortable temperature. It also seems more likely to be possible to make it look like an intentional aesthetic feature rather than a bolted-on mechanical system.

It's sometimes hard for people steeped in the lore of 1970s passive thermal design to get their heads around the advantage of low thermal mass sunspaces, but the theory is sound and they have been tested successfully. Most of what I've seen is DIY projects using discarded materials, and those are of course cost effective, since the cost approaches zero. It seems much less likely that a professionally built version with new materials would be cost competitive with the current favorite of grid-tied PV + minisplits as a means of solar heating, but I haven't seen an analysis.

Regardless of cost competitiveness, they could also be useful as a way for people who are sentimentally attached to the idea of (semi) passive solar heating to have that feature and have it work better than a classic 1970s design, even if it's not strictly speaking cost effective. (There are plenty of other things that people incorporate in buildings for sentimental reasons without demanding that they be cost effective.)

Oct 9, 2015 9:58 AM ET

Edited Oct 9, 2015 10:01 AM ET.

Response to Charlie Sullivan
by Martin Holladay

You wrote, "One idea that has recently been tossed around and tested as a different way to re-think passive solar design is a low-thermal-mass sunspace that is insulated from the house, but connected by operable vents, usually with fans."

I was struck by the word "recently" in this sentence.

This is a very old idea. In fact, Alex Wilson wrote a GBA blog about his work building this type of sunspace during the 1970s; if you want to reread his 2011 blog, here is the link: Sunspaces - Solar Heat and a Place to Grow Plants. He included a classic 1970s photo showing three idealistic hippies assembling such a sunspace in New Mexico. (I'll attach the photo below.)

I built one myself in 1975 -- using old window sash I gathered for free, of course. I used it to start vegetable seedlings. Of course, the space froze -- I eventually bought and installed a kerosene space heater to try to keep the plants alive.

There are very, very few hours during a year when these spaces are comfortable. They are almost always too hot or too cold, so you won't see many people sitting in their sunspaces with a smile on their face.

Used as you describe, they can add a little bit of heat to a house. Are they cost-effective? Absolutely not. There are about 500 other measures that a homeowner should invest in before spending thousands of dollars on this type of sunspace.


Sunspace - 1970s.jpg

Oct 9, 2015 10:32 AM ET

by stephen sheehy

On the south side, our old house has a minimally insulated porch with lots of windows. We access it from the house through some exterior French doors. In winter, on sunny days, it gets hot, but we just open the doors and let the heat into the rest of the house. We used the space frequently, all year long. When it's really cold, like -15, it freezes, but it never gets cold enough (below about + 15) to kill the rosemary plants we leave there in the winter. Of course on cold days, it is clear and we generally get sun.

Our new house has a similar room, outside the conditioned space, but with pretty good insulation and pretty good (U-.25) windows. When winter arrives, we expect it to collect sunlight and heat and we'll open the room to the rest of the house. It really never overheated in the summer. On sunny days we just open the windows. Of course in Maine, it rarely gets really hot. We used the room a lot, all summer long and were never uncomfortable.

Oct 9, 2015 10:51 AM ET

Edited Oct 10, 2015 5:27 AM ET.

Response to Stephen Sheehy
by Martin Holladay

Thanks for your balancing comments. You're right, of course: some sunspaces can be comfortable for many days of the year. The least comfortable sunspaces have sloped glazing or glass roofs; the most comfortable sunspaces have conventional (insulated) roofs.

That said, homeowners who invest in this type of room should be aware that the investment won't be a cost-effective way to lower their energy bills. It's simply another room -- one that may be delightful and worth the investment (because of the pleasure it provides), but not one that can be considered an energy feature.

For a humorous look at a home where the occupants got fed up with an uncomfortable sunroom -- so fed up that they made drastic modifications to the sloped glazing -- see South-Facing Skylights: Threat or Menace?

Oct 9, 2015 11:58 AM ET

reply to Martin
by stephen sheehy

I agree. A sunny room should be delightful, but will hardly be cost effective from an energy standpoint. But most of a house isn't cost effective if one looks at energy inputs and outputs.

Let's face it. Most houses are lousy investments if you just look at the numbers.

Oct 9, 2015 12:01 PM ET

East west orientation still important
by Dana Dorsett

The east-west orientation is still important, not for passive thermal gains, but for higher energy yield from fixed rooftop photovoltic panels. When PV panels become north of 30% efficiency this fades a bit, but it's hard to get to Net Zero without quite a bit of optimally oriented PV panel real-estate at current 15-22% efficiency commodity silicon panels.

Oct 9, 2015 12:10 PM ET

Response to Dana Dorsett
by Martin Holladay

That's an excellent point. It may have nothing to do with passive solar design, but your point emphasizes an important truth: if a builder wants to prepare for our solar future, the most important thing to do is to think about where the PV array will be installed.

Oct 9, 2015 12:43 PM ET

Charlie, Martin, and
by Eric Habegger

Charlie, Martin, and Stephen,
I have a variation on the idea of a low thermal mass sunspace that may be very workable. I'm still working on it (and I'm taking my time about it). You may not actually have to create a low thermal mass space that you will live in. What I'm doing is using the space just below the roof sheathing as my "sunspace". I have not attempted to create a roof with a low (or is it high?) reflective index. Instead I've used normal darkish shingles and I have painted the underside of the sheathing flat black. The idea is that whatever heat the plywood sheathing has absorbed will have an easy path to reradiate that heat in a downward direction.

To compensate and contain this low resistance path for infrared radiation I've stapled a standard aluminized radiation barrier to the underside of the rafters. This helps in stopping the heat from overheating the attic and then the living space. It is imperfect though because of the thermal bypassing at the rafter edges where there is no air space between the rafter and the radiation barrier.

The hardest part in constructing this has been in creating the controllable vent through the roof with a motorized damper. The first damper I put up there has stopped working. It may be that the heat has fried it. I measured a heat up there once of 155F! It may be time to change out the damper to a manual one with a system of pulleys. That's on the back burner right now with other work I have.The other part of the system was to tie the radiant barrier into a duct that channels that hot air into the living space. It also requires a damper but I expect that damper to be motorized and long lived. This system will required a fan to bring that air into the living space.

The operational idea is to open the roof damper once one is outside of the heating season to allow the roof to cool off normally in spring, summer, and fall. Normally one should only have to open or close the roof damper two times a year, so a manual damper will work fine. In winter that damper is always closed but the damper to the living space is opened and closed daily. When the thermostat in the rafter space is above 75F or so this damper is motorized open and the fan brings the air into the house. When the house is warm enough, or the temperature in the roof cooled down too much that damper is closed. Remember, there is not a lot of temperature inertia in the roof. You have to use the heat when its there. The whole point is that you have enough insulation and tightness in the living space to keep the house at whatever temperature it gets to and to keep it there long enough to reach the next useable heating cycle on following days.

I think this idea is a much more useable idea than a sunspace for the reasons Martin gave. You aren't required to live between the raters. Thank God! And you have the whole vast expanse of the roof to collect heat.

Oct 9, 2015 1:25 PM ET

Response to Eric Habegger
by Martin Holladay

You are creating an inefficient solar air collector.

Your scheme has all of the usual disadvantages of solar air collectors -- most prominently, the fact that the cost of the hardware exceeds the value of the collected heat -- with a few additional disadvantages (for example, the fact that the absence of glazing lowers the temperature of the heated air).

Remember, the damper that you have designed to allow heat to enter your house will leak a little bit of air, so that your contraption will degrade the airtightness of your home's thermal envelope.

For more of an in-depth look at why your investment won't yield enough energy to justify the cost of the hardware, see Solar Hot Air Collectors.

One final point: in many climates, snow will impede the function of the system you describe -- and the snow tends to occur on the days when the heat you are trying to collect is most needed.

Oct 9, 2015 1:47 PM ET

Martin, I'm not so sure you
by Eric Habegger

Martin, I'm not so sure you are correct in your assessment. You are interpreting this idea from a Vermonter's perspective. That's OK. I'm likewise interpreting it from a Californian's perspective. That's OK too. We probably should both have stated that up front.

I think the idea that a damper having an air leak may be a red herring. Doors and operable windows also may have air leaks. Yet most superinsulated houses still have them and it doesn't keep them from being superinsulated. Of course I'm not trying to imply my home is superinsulated. It isn't. But one can't play fast and loose with principles to win an argument. It's the details that count.

The idea I'm playing with really isn't the same as solar hot air collectors. It depends instead on high volume of low quality heated air. This is the opposite of solar hot air collectors. I'm surprised you didn't pick up on that. I'm not at all saying that I've developed a proven idea because I haven't proven it. But I think you are too quick to lump it in with an idea you know about and concluding its the same.

Also, you missed the biggest potential disadvantage to my idea: It might replace valuable real estate that could be used for PV. PV placed on a roof might cool the roof enough that the idea would no longer be useable.

Oct 9, 2015 1:59 PM ET

Response to Eric Habegger
by Martin Holladay

Believe it or not, I did understand your proposal. Even in California, the net effect of your scheme (useful heat gained minus heat lost through the operable damper) will be quite low, and will not be enough to justify the cost of your hardware.

One reason is that the volume of 140 degree air isn't large enough to hold much heat. (I know you think that the volume of air between your rafter bays is large, but the amount of useful heat held there is small.)

Lots of people have tried out this scheme, and every other variation of the "solar attic" -- including glazed solar attics and unglazed solar attics. These are old ideas from the 1970s, and they didn't pan out.

Oct 9, 2015 3:58 PM ET

by Lukas Peter

Great summary!
I am not ready to drop the importance of east-west orientation for another reason. Doesn't cooling and glare become a real issue in a north-south oriented super insulated house, any house? If a house isn't oriented east-west a larger percentage of it's window surface is more likely to face east and west. I understand that trees can provide shading but how do energy calculations take this properly into account so equipment is sized adequately?

Oct 9, 2015 5:22 PM ET

Response to Martin (#2)
by Charlie Sullivan

Martin, thanks for the illustrated history lesson (#2)! Although I was alive in 1970, I was building only with tinkertoys at that point, and my tinkertoy set didn't include any glazing.

My sense of the history was that first people built sunspaces, without thinking about thermal mass much. When their seedlings froze and died, they started thinking about thermal mass and the accepted wisdom became that high solar mass was better. I didn't realize that people had been deliberately minimizing thermal mass in sunspaces or understanding that doing so would increase their heat yield until more recently. And Alex Wilson's blog only mentions thermal mass as something to add to prevent freezing, not something to avoid in order to maximize heat harvesting. Maybe that was considered too obvious to mention, but regardless of whether the folks in the 70s understood that minimum thermal mass could lead to maximum heat harvest, that concept is missing from most descriptions of the sunspace approach.

Anyway, we agree that sunspaces are not anywhere near the top of the list of cost effective improvements, and we agree about when you would want low or high thermal mass in one, and we agree that one can't count on them being at a comfortable temperature much of the year.

Oct 9, 2015 5:51 PM ET

Edited Oct 10, 2015 6:51 AM ET.

Response to Charlie Sullivan
by Martin Holladay

Every imaginable variation on the sunspace was built during the 1970s -- both low-mass sunspaces and thermal-mass-equipped sunspaces like those advocated by Steve Baer.

Organic Gardening magazine, Mother Earth News -- all of the magazines had instructions on ways to tack on a sunspace on the south side of your house, using polyethylene, old windows, new windows, Kalwall panels, or patio door replacement glass -- with or without concrete or 55-gallon drums of water.

Of course, when the sunspaces overheated, the hippies installed fans that blew the hot air into the house. When the sunspaces froze, the hippies added heaters or exterior insulated shutters. Every imaginable experiment was conducted, I think.

Oct 9, 2015 10:35 PM ET

Great blog!
by Malcolm Taylor

The ideas in Mother Earth News or Harrowsmith may not have all panned out, but as you say, the almost endless variations on a theme have left a legacy of what works and what doesn't. I love the architect's drawings from that era. Full of annotations and arrows indicating solar gain and views - as though they were physical objects in the building.

Oct 10, 2015 5:09 AM ET

Edited Oct 10, 2015 5:17 AM ET.

Response to Malcolm Taylor
by Martin Holladay

We've all been misled in the past by the "smart arrows" -- the ones indicating air flow -- on architectural drawings. I certainly remember prominent "smart arrows" in every article I read about double-envelope houses.

The curse of the smart arrows is still with us, unfortunately. For example, drawings of ventilated flat roofs (or roofs with a 1/12 slope) often show air entering at the "soffit" and leaving at the "peak." (Right -- that's going to happen.)

Oct 11, 2015 5:14 PM ET

Edited Oct 14, 2015 11:35 AM ET.

Two parallel threads of comments
by Martin Holladay

GBA Prime subscribers should be aware that this week's blog exists in two versions: the traditional behind-the-paywall version and a "sneak peak" version offered to whet the appetite of non-subscribers.

There are now two parallel threads of comments, so interested GBA Prime subscribers might want to check out the comment thread on the article on the free side of the paywall: GBA Prime Sneak Peek: Reassessing Passive Solar Design Principles.

Oct 13, 2015 10:18 AM ET

Hidden Benefits to Passive Solar
by Andrew Bater

This is an interesting article and comments. To be honest I am not sure whether I would build a passive solar home again, the cost/benefit ratio is not what one would hope. However my observations tell me that there may be other hidden benefits not discussed here yet.

For example, the coldest winter nights of the year are almost always followed by days with brilliant sunshine. (I think the lack of insulating cloud cover is part of the weather equation.) So on a -10 degree night our geothermal unit will be cranking away, slowly dropping the loop temperatures, becoming less efficient by the hour. But by the middle of the next day solar gain will heat the house on its own, the geo unit shuts off and the ground loop temps recover. Pretty neat to observe.

Oh and cats, cats love to live in a passive solar home...

Oct 13, 2015 10:42 AM ET

Response to Andrew Bater
by Martin Holladay

You wrote, "On a -10 degree night our geothermal unit will be cranking away, slowly dropping the loop temperatures, becoming less efficient by the hour."

It should be noted that if your house had fewer south-facing windows, your heat pump wouldn't have to work as hard on cold winter nights.

Oct 14, 2015 10:59 AM ET

Thank you Martin
by James Morgan

Great article summarizing all that we've had the opportunity to learn about this subject - often the hard way - over the last forty years. Ah, the (sometimes) glorious mistakes! The most significant residual meaning of 'passive solar', to me, is the pleasure of taking a nap near a sunny window on a cold winter day. I only wish this article was available outside the firewall so that I could point clients to it. We have to have this discussion again and again. It could save an awful lot of energy that way (mine).

Oct 14, 2015 11:15 AM ET

Orientation notes:
by James Morgan

One, I recall reading a while back that at least one California utility was paying customers to point their grid-connected PV panels to the west so that the greatest output occurred in the late afternoon when demand was also greatest. The panel does not generate its maximum output in this orientation but for this utility it does produce its maximum *useful* output.
Two, most homes being built today do not enjoy the luxury of choosing their solar alignment in any case. They face the street, period. Few developers pay much attention to the affect of subdivision layout on solar performance. And the vast majority of individually-designed non-subdivision homes which *can* choose their orientation are built out in the boonies, bringing a whole range of secondary resource penalties such as transportation dependence. Of course this is a whole other discussion area, one which GBA seldom gets into.

Oct 14, 2015 11:35 AM ET

Response to James Morgan (Comment #20)
by Martin Holladay

You wrote, "I only wish this article was available outside the firewall so that I could point clients to it."

As I already noted on this page (see Comment #17), this article is available on the free side of our paywall. Here is the link: GBA Prime Sneak Peek: Reassessing Passive Solar Design Principles.

Oct 14, 2015 11:43 AM ET

Response to James Morgan (Comment #21)
by Martin Holladay

You wrote, "Most homes being built today do not enjoy the luxury of choosing their solar alignment in any case. They face the street, period. Few developers pay much attention to the affect of subdivision layout on solar performance. And the vast majority of individually-designed non-subdivision homes which can choose their orientation are built out in the boonies, bringing a whole range of secondary resource penalties such as transportation dependence."

Good point. The same point was also made in the thread of comments on the parallel page for this article -- the version in front of the paywall -- by GBA reader Peter Amerongen (see Comment #14 on this page: GBA Prime Sneak Peek: Reassessing Passive Solar Design Principles).

Peter wrote, "Unfortunately, good solar access is pretty rare in the dense urban places where we should be building. It makes no sense to piss away the savings to be had from that perfect solar site by driving back and forth to work every day."

Oct 14, 2015 1:17 PM ET

Variations on a Theme
by Jim Baerg

Thanks Martin, I largely agree with you, and have followed those trends in my own design and construction practice. I would like to add the following points which are intended to broaden the discussion beyond your "technical" and "economic" concerns.
First, local climate matters. Many of the early high mass Passive Solar houses were built in the New Mexico highlands where there is real winter, regular sun and predictable diurnal swings. With summer shading, I would think that Passive Solar could work well there. Personally, I would modify your design suggestions with an eye towards regional variations in weather. There are plenty of places in the country where some version of the Passive Solar/PassivHaus continuum can work well if carefully designed.
Secondly, the windows we now have available offer us much better performance and design flexibility. We no longer need to be held captive by building orientation and that is important in urban settings. Still, if there is good sun in a cold climate, cheap fixed glazing that is limited in size can make energy, performance and economic sense. Decreasing window sizes on the NWE sides and increasing Southern glass by a moderate amount can actually be cheaper than a regular arrangement. As such, there is no cost penalty.
Finally, This discussion leads me back to the old question of unique designs vs. housing standardization. For me, livability has become increasingly important as we button down our houses. Strategically placed windows, to capture the sun, the views, and the ever changing light are essential to my sense of well being. There's nothing better than warm sunlight flooding the house on a winter day. Personally, I think that grounding house design in local conditions, where the house responds to weather and the land, is as essential as high insulation levels, air tightness and moisture control.
This is, of course, an argument for the art of house design. Equally important is how do we get to affordable/standardized housing that works well, which seems to be your starting point. I very much appreciate the clarity that your article brings to the discussion and the need for general design principles, but would like to see every article and response include some mention of local climate.

Oct 18, 2015 11:42 AM ET

Response to Martin Comment #22
by James Morgan

Thanks Martin, this is definitely a post to be widely shared.

BTW, I did click on your link earlier but it led me to a different, barely related post. Maybe my browser had a code fart.

Oct 18, 2015 12:24 PM ET

Response to James Morgan
by Martin Holladay

Yes, the link was bad before I corrected it. Sorry -- I hope it works now.

Nov 8, 2015 8:00 AM ET

There always needs to be a compromise
by Howard Kelley

Firstly, I have received great wisdom here from many people and I appreciate that. Thank you.

2 houses and a large shed. .... I had built an E/W, south facing passive solar, big over hangs, Russian stove heated, timber frame ... it was great, it had a 15-20 degree temp swings, (upper 70s day, 59 by am., but you adjusted ... and I was 29 and thought it was great.
All most no heating bills, but you really needed sunglasses a lot. The Vermont Architect had me add 2 awning windows that were up at the peaks, on the ends that were open 8-9 month a year to varying degrees, just like in an old barn. Each May we put up Awnings across the S facing front and with big sliders to capture air, a screen porch on the N. side and the peak windows, it was fully comfortable on most summer days. (What happened next, I sell the home, a year layer there is an accidental fire, they build new the next owner immediately put on a front porch, blocked the sun, and put in a traditional heating system. And so it goes. )

Pro - Bright and winter toasty, low energy costs... Con .. a little too warm in the shoulder months, awning maintenance, my wife didn't really care for the temp. swing, but fans and Russian stove worked on that. There were compromises and nothing fully black and white.

Fast forward 20 years, I purchased a highly insulated Cape with the wrong orientation, I have adapted this place 3 different ways to tomorrow, with more glass, more insulation, porch adaptation etc.., PV system.. it all works reasonably well. This also has awnings... everyone should use awnings, they add charm and really work. I do not care for this house nearly as much.

Pros, traditional, lives reasonably and mostly efficient. Cons - the wrong axis forces fossil fuel usage, lights, heat etc .. due to rm layout and livability. Pro and Con are really the same as I am the enemy, I am far too aware of thermostats and light switches, even though we have PV and almost no electric cost. More wife likes this place better.

The Shed is a hybrid- it has the right axis, windows mostly south, 2 ft over hang roof, summer awnings, fully vented metal roof, insulated concrete slab floor w/ pex installed, one floor 1800 sqft.. Ice and water wrapped, 6" + recycled foam on the external walls and 8" external ceiling,
The Compromises first, I would rather have more solar gain in the winter, bright and warm wins. Having to open a venting window or large doors is the compromise. Nothing too mechanical please, it costs a lot and low ROI,. The compromise of Awnings and airflow will resolve most summer issues. It is the magical mini-split, that will be needed most, to take the edge off winter and summer. (there may even be an issue with those mini-splits), The slab will also play a role in some way. PV will be added before the end of 2016, This building may never actually go on to the grid.

If you have a growing family, there will be compromise, parents moving back in compromise, retrofit compromise, the technology compromise, millennial compromise, the Uberization compromise, the Financial compromise. Being in the RE Brokerage business, with emphasis on Marketing and Sales, I can attest to less is usually more, technology is as much a trap as a help, there is always something new.... and time tested design, products and methods usually win.

Sorry for the soap box turn, but I just read about the Romans and the aqueducts, the mini-split cop efficiencies and then passive solar ... I couldn't help myself. The sun wins in multiple ways, the technology of insulation wins, the idea of simple planning and design wins and it must have financial and environmental sense. I'm done. Thanks.

Nov 8, 2015 10:03 AM ET

Edited Nov 8, 2015 10:05 AM ET.

Response to Howard Kelley
by Martin Holladay

Thanks for sharing your experience. It's all relevant, and it all rings true.

Indeed, the energy nerd often has different expectations and desires from the energy nerd's spouse. This raises many questions; for example, why is it that the energy nerd is willing to accept wider indoor temperature swings than the energy nerd's spouse? Is it because the energy nerd, by definition, is invigorated by these temperature swings? Or is it because the energy nerd is willfully blind to data that don't fit the energy nerd's world view?

Been there...

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