1. How is a (Certified) Passive House different from a passive solar house? The phrase passive solar house is often used to describe any house designed with lots of windows facing the sun in winter in hopes of getting some of the heating energy from the sun. Done right such a home would have some thermal mass inside to store solar energy and help prevent overheating, overhangs for summer shading, and would be well insulated, but often homes are marketed as being passive solar homes without any energy calculations done to balance all these components and make sure they work together, and that has given solar homes a bad name over the years. A Certified Passive House is a passive solar home that was designed starting with the energy calculations needed to be sure the building is super-insulated and airtight enough that the passive solar energy coming into the house provides nearly all the energy needed to keep the house warm in winter and cool in summer. In fact, the Passive House Standard that all Certified Passive Houses must meet requires that the backup heating energy the house needs can’t exceed 15 kwh/ sq. meter treated floor area annually. This amount of energy is so low that peak heating demands almost never exceed 1 watt per square foot, such that a modest 1200 square foot house can be heated with about a 1200 watt electric heating element (about the size of a hair blow-dryer or toaster) in the fresh air supply duct, and no furnace or boiler is needed.
2. What’s green about foam walls made from petroleum? Most foam products are made from petroleum and thus have a high embodied energy (the energy that goes into making a product from extracting a natural resource to delivering a finished product to the user), but building insulation generally saves multiple times more energy in heating and cooling than ever goes into its manufacturing. Therefore the typical code-compliant American house will use far more energy in its lifetime (embodied energy+ operational energy + disposal energy) than our Passive House does, even though it has much less embodied energy built into it. And the petroleum that went into making our foam walls will never be burned and turned into greenhouse gases, but will remain safely sequestered behind the concrete skins of the house. We look forward towards the day when EPS foam insulation made from agricultural crop sources (bio-foam) can be used in structural building applications like our walls, but the industry isn’t quite there yet – none of the very expensive structural engineering tests have been done on bio-foams yet.
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