Passive Houses Demystified

Passive Houses (from the German Passivhaus) are super-low-energy buildings that allow us to avoid the volatility of fuel prices, reduce our reliance on fossil fuels, and help protect the environment. Many may still remember the oil crises of the 1970s, when, after decades of cheap fuel, we suddenly experienced fuel shortages, waiting lines at service stations, and staggering price increases. Before that, the price of gasoline had hovered around $0.25 per gallon for a long, long time; since then, we have seen highs of $4 or more, and we are now, but probably only temporarily, enjoying a price of around $2.50 per gallon – 10 times what it cost before the 1973 oil embargo! Passive Houses were first developed in Germany in response to the 1973 oil embargo, and they are now being designed and built in North America in increasing numbers due to our growing interests in energy independence and a healthy, sustainable environment.

Passive Houses achieve their super-low-energy status by being extremely air tight (minimizing heat loss through air infiltration) and extremely well insulated (minimizing heat loss through conduction, convection, and radiation). Passive House standards exceed most energy code requirements for air tightness, insulation levels, and controlled ventilation.

Passive Houses include controlled ventilation systems that recover heat from exhaust air and transfer it to incoming outside air to provide fresh, tempered air for the health of building occupants.

Passive Houses avoid fuel price volatility by minimizing or even eliminating reliance on fuel combustion for building heat. Yes, we need to pay somewhat more for insulation and air tightness, but, once built, those features can continue to return benefits without being subject to price spikes.

Air tightness is the real champion of energy efficiency in any building, and it costs less than added insulation, high performance windows, or other features. Today, air tightness is measured with blower door tests that quantify the number of air changes per hour allowed by your building envelope. Little cracks and gaps can add up to a lot of air infiltration and heat loss, but they are comparatively inexpensive to eliminate through air sealing techniques including tapes, gaskets, and other closures selected specifically for the application. Your building might have really good, energy efficient windows with gaps you can’t see behind the interior trim that cause uncomfortable drafts and wipe out all the value of the really good windows; but removing the interior trim and applying an appropriate air sealing tape before re-installing the trim can virtually eliminate the gaps and the related heat loss through infiltration.

An energy audit on my own 1970s house a few years ago highlighted the bad effect of a small hole made years earlier to bring a propane line into the house; the unsealed opening around the propane line (only a fraction of an inch in size) let a tremendous amount of cold air into the wall cavity, and the wall area near the small opening showed up as a large cold zone in a thermal image of the wall. Another surprising find was a poor eave insulation condition that let outside air drop into the wall construction behind the interior finish in a small added room; the attic was well insulated, but the eave condition defeated the value of the attic insulation. Energy audits are very inexpensive these days, and they can be very revealing about the actual performance of your building, allowing you to isolate problem areas to address with improvements. With simple, inexpensive air sealing of gaps revealed by the audit, I was able to reduce the air infiltration in my house by 15%, as measured by a blower door test in a follow-up audit.

Not everyone can transform their building to Passive House standards, but the Passive House goals are valid. Net Zero (a label with increasingly popular appeal) is about generating (from renewable sources) an amount of energy equal to the amount of energy you use in your building. So, it makes sense to use less energy in order to be able to achieve Net Zero status with less generation – fewer photo-voltaic (PV) solar panels, for example.

Architects, builders, and their clients are paying more attention to Passive House standards as the benefits become more widely known and appreciated; and consumer pressure for these benefits is likely to be most influential in causing related advances in the building industry.

Visit http://www.phius.org to learn more about Passive Houses in the U.S.

Posted in Design, Energy Efficiency, Passive House

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