Building a “passive house”

Michael Giberson

Many critics of smart grid-related ideas for saving energy object that consumers won’t want to sit around watching energy prices, flipping light switches and delaying the dishwasher when prices spike now and again to save a few bucks. Of course the critics are right on this point. The best smart grid energy saving ideas are mostly in the realm of “fix it and forget it” devices. You set the dial and let the device do the work.

Perhaps the ultimate “fix it and forget it” device for home energy saving is a passive house – a house that is designed and built to require minimal amounts of energy. This isn’t a smart grid kind of thing – these designs are so smart that they can be dumb; they don’t need to know the price of electricity.

Or rather, because a passive home design requires additional upfront effort and expense, the smarts need to be exercised mightily up front. As discussed in an article in the New York Times describing a passive house being built in suburban Boston central Vermont (edited, see comments), such homes are more expensive to design and build. After that, it is mostly “fix it and forget it.”

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7 thoughts on “Building a “passive house”

  1. The house is not in suburban Boston; it is in Norwich, VT, nowhere near Boston except in intergalactic terms. The owners live in suburban Boston but are building in VT (near Dartmouth College by the way.) And as far as price is concerned, this is a fairly high end place. A passive designed home can be done much more reasonably. It might not be a zero energy home, but could be much more efficient that a standard house just by aiming south and with proper glazing on the south side, and overhang and enough mass to moderate temperature swings.
    But you are correct, proper siting of homes can do a lot to reduce energy usage.

  2. The NYT article is interesting from two perspectives. First, it highlights the attention to detail required by the passive house standard. Building every home in a new development to face directly South would present some interesting planning and architectural design challenges.

    More important, I believe, it highlights the limitations of energy retrofit programs for the existing housing stock. That is not to suggest that the existing housing stock cannot be improved, but rather that the improvements which can be made are limited and can be very expensive. Retrofitting the existing housing stock with under-slab insulation, 18″ sidewalls, etc. is clearly impractical. Rotating existing houses to face South might be a real technical (as well as political) challenge.

  3. I’d be interested in seeing a careful analysis of passive house energy economics. Given the added expense of building a passive house, I wonder if we are embedding energy in the form of extra insulation and materials up front in order to reduce energy consumption later. Of course if you expect energy to become more expensive, it might be a good idea to buy more energy now in order to buy less energy later. On the other hand, if energy is become cheaper in the long run, then maybe not such a good idea. It is a complicated and interesting issue.

  4. Ah, I confused the story’s mention of where the family currently lives with where the new home is being built. The linked video describes the location as central Vermont.

  5. Mike,

    It is highly unlikely that energy will become less expensive in the US. The federal fascination with “pricing carbon” to raise revenue and possibly also reduce carbon emissions would drive the prices of electricity, natural gas, propane and gasoline up. New coal mining regulations and restrictions would increase the price of coal and thus electricity. New regulations for mercury emissions from coal-fired generators would also increase electricity costs, as well as result in the closure of many older, smaller coal-fired generators. New demands for mass transit funding and high speed rail would likely lead to an increase in the federal gasoline and diesel taxes. Actually reducing US carbon emissions by “83% by 2050” would require the investment of ~$30 trillion over the period, over and above the “business as usual” case, requiring an approximate 10% return on investment.

    The incremental investment in the passive house is mostly in long lived materials, which would likely be recovered eventually, though that would probably require great patience and a long life.

  6. The article was interesting, but without understanding how much building a house this tight costs, and what the problems are*, we are not sufficiently informed. Energy conservation is good, but it is not infinitely good.

    * e.g. mold. A tight house can be infested with mold much faster than a leaky house, which can dry out faster.

  7. The basis of Passive House is cost-optimized efficiency. That is, a detailed computer model of the building and its environment is created and modified to find the point where mechanical systems can be reduced and/or eliminated due to high performance. This process also allows for compromise and tradeoff (material and construction alternatives, less than optimal orientation, etc.) making it quite architecturally flexible yet still technically informed. In Europe, where there’s a 20 year industry around Passive House, life cycle costs are no lower than with Passive House and up front construction costs range between 0 to 8% extra. Note that most of the products and materials are typical building materials, neither exotic nor imported – we’re just early on the learning curved in this country.

    As far as mold problems, quite the opposite is true. In a properly designed tight building, where the building assemblies have been designed to permit drying (ie, the “walls can sweat, but not breathe”) up to 90% of the source of internal moisture delivery is removed, that being warm, moist air. Past problems were largely due to “walls that could breathe but not sweat.”

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