Passive House vs. Passive Solar: A Continuing Discussion

| 4/15/2014 2:12:00 PM

Tags: ask our experts, green homes, passive house, passive solar, passivhaus,

Passive House HomeIn our April/May 2014 issue, we ran Passive House: Beyond Passive Solar in Ask Our Experts, which discussed the differences between passive solar design and Passive House standards. In response, we received a letter from architect Richard Schmidt of San Luis Obispo, Calif., questioning a number of points in the article. We’ve posted his letter below, and we’d like to hear your thoughts as well.

“Your article ‘Passive House: Beyond Passive Solar,’ intended to clear up confusion between ‘Passive House’ and ‘passive solar,’ merely adds to the muddle. The only connection between the two is the word ‘passive.’ The building philosophies behind the two could hardly be more opposite, nor is there, as the title of the article implies, the slightest evolutionary relationship between the two. To state that Passive House is superior to passive solar is just plain nuts. That’s like saying apples are superior to tomatoes — a proposition few MOTHER EARTH NEWS readers would buy.

“One of the problems with current building codes and conventional thinking about what makes an energy-efficient building is the codes’ obsession with energy conservation at the cost of energy generation/collection/conversion. Passive House is code-type energy conservation on steroids — a super-airtight, super-insulated building envelope of industrial materials dominates the process. A Passive House, it is sometimes said, can be heated with a light bulb, which sounds fine until you think about how you get there: petrochemical insulation far beyond what’s probably needed; layer upon layer of petrochemical housewraps, vapor barriers and the like; a house that’s so tight you have to run mechanical ventilation 24/7 to control mold and condensation and keep it pollution-free; and paranoia about energy loss through windows so much that windows are often minimized, creating cave-like interior spaces more suited for spiders than human comfort.

“In fact, contrary to your article’s implication that Passive House is merely a souped-up version of passive solar, many Passive House designs exclude winter sun because the building would overheat if sun were allowed to pour into the interior. To top it off, there are the politics of Passive House: One has to follow a set of one-size-fits-all rules to get ‘certified,’ and the competing Passive House certifying groups can’t even agree on just what that entails. This is a very expensive and highly questionable way to build.

“Your writer dismisses passive solar as ‘popularized in the 1970s’ (1970s? Boo! Hiss! Orange bathroom tile! Old technology!). Actually, passive solar embodies timeless energy principles largely ignored by most building codes and not embodied in Passive House. Until the era of cheap fossil fuel, this was the common way of building in much of the world. Then we forgot it, and now, we’re told by MOTHER EARTH NEWS to do something called ‘Passive House’ instead. That is a mistake in clear thinking.

“All building sites have natural energy flows that can — and should — be captured for use by the buildings we put on them. Passive solar heating and cooling — letting in the sun’s winter warmth, storing some for later, keeping out the sun in summer when we don’t want heat — is one means of tapping these basic energy flows, which we can capitalize on free with good design. In places with sunny winters, why not make capturing this free heating energy — with its added bonus of brightly lit rooms that cheer us during winter’s short days — our top priority? If we ever hope to get off the fossil fuel treadmill, it will be through capturing passive energy flows — passive solar heating, passive ventilation, passive cooling and the like. All of these techniques require some thought about how to design a building — they’re not good add-ons, because buildings need to be sited and configured to make the most of nature’s passive energy flows. We also need to fight to get energy generation given coequal status with energy conservation in building codes to make designing for passive energy conversion routine.

10/16/2014 10:27:39 AM

Passive solar design from the 70's was an important evolutionary step and we learned many lessons (including the fact that most attached solar greenhouses, as designed then, were too hot in summer and too cold in winter). However, it is possible to design a passive solar home that is still inefficient, and in most parts of North America, passive solar design is NOT enough in an energy and carbon constrained world, as high cooling and/or heating loads will still lead to high carbon dioxide emissions from fossil fuel use. PassivHaus is a PERFORMANCE standard, not a prescriptive standard, and based on research, certified PassivHaus buildings meet their targets, including no more energy use than 15 kWh/m2=or 1.4 kWh/sf and year for heating and cooling (though with a fair amount of variation around the mean). Any good PassivHaus designer worth her (or his) salt, will use passive solar design as a starting point, as solar gain is part of the required energy modeling. So homes that are " creating cave-like interior spaces" are signs of poor design, not PassivHaus design. PassivHaus buildings have sophisticated systems for ventilating a house when the weather is mild (among PassivHaus experts it is referred to as an "openable window"). However, in climates that get hot or cold, it makes no sense to ventilate without heat recovery during weather extremes. This also ensures high indoor air quality and adequate supply of oxygen, unless many non-ventilated leaky homes that may get too much air when it is cold and windy (i.e. unpleasantly drafty), and not enough when there is no wind and not sufficient temperature differential between indoors and outdoors to ensure adequate air supply. By contrast, PassivHaus provides a constant gentle air-flow during the cooling and heating season.

6/15/2014 6:41:22 AM

I would like to thank Richard Schmidt for his response on the question on Passive Solar vs Passive House. My husband and I build a passive solar house using 'old technology' and couldn't be happier with the results. We looked at the passive haus standard and from our simplistic approach and looking at our budget we decided that simple, less gadgets approach was more in keeping with our life philosophy. The 'free with good design' was exactly what we went with. We hired an architect who went to our building site to pick the perfect elevation and orientation and that was the best money spent on our project. We didn't use infloor heating as that defeats the whole process of using the sun's energy to heat your floors. We also went with earth berming rather than using a mechanical geothermal system. When we have had students out to view our house they want to see the mechanicals and what we have is simply the least amount of expensive, need to repair/fix items in our house. If we could have, by law, gone with a passive ventilation system, we would have. In this case less is more. To view our house on youtube go to Thank you to Mother Earth to bringing the topic back to the surface from 1970's....on a side note I wrote a book from an 'owners' perspective and when it was delivered the library, the librarian said he was so pleased to have an 'updated' version since all his books on passive solar were from the 70's I didn't have the heart to tell him that was the version we were working from in building our house. Have a great day, Tracey Allen Author of Building a Passive Solar House: My Experience Shared

5/8/2014 12:16:05 AM

Richard Schmidt is right. Buildings need to 'breathe' the way human lungs do, to be fit for occupancy. 10 years in a 1980's 'energy tight' home with formaldehyde fake wood and other petrochemicals causes asthma, allergies, other major health issues. People are suffocating in these buildings. The hay bale method sounds really great.

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