The area's first Passive House is almost ready for prime time. We reported earlier about the basics of the deal, but here is a more lengthy discussion on the watts and kilojoules that are happening behind the scenes. The house is on the market for $1.6 M and will soon be open to the public, though it is already attracting a lot of attention from the local media.
First things first. Check out the windows along the left side of the house. That's the southern side, which will get the most sun so they are built to maximize the amount of warmth that enters the house and increase the ambient temperature as much as possible. Eventually they will have mechanized awnings which extend in response to the sunlight outside so that in the summer the house will be cooler.
The next crucial step is building an airtight seal so drafts don't bring down the temperature. That requires a whole lotta tape and a whole lotta quality control. During the build any contractors who wanted to drill a hole had to check the drill out from the foreman with the key. For the entire house, every hole to the outside is accounted for and there are about two dozen for things like sewer lines, water pipes, and ventilator intake and exhaust ducts. The ventilation system is another unique piece of a Passive House, and is crucial in the humid summers of D.C. to prevent mold and mildew from overtaking the place. This calls for an Energy Recovery Ventilator (pictures 2 and 4) and a few filter changes each year.
To meet Passive House certification criteria the house has to pass the Blower Door Test which measures the amount of air changes per hour. For a Passive House the number of air changes has to be less than .6 changes at a pressure of 50 pascale (it takes about 10 pascale to lift a drink about an inch inside a straw). They use an infrared camera to see where the air changes are occurring and tape them securely so no air passes through.
The third big part of building a Passive House is to insulate the walls and foundation with thick, high density foam. Check out Curbed's earlier post for a picture of the twelve-inch thick walls, which show the foam layered against the concrete for a better guarantee against Snowmageddon.
· Bethesda Passive House [official site]
· The Newest, Greenest House On The Block [NBC Washington]
· Passive Houses Aggressively Reduce Energy [USA Today]
· Windows To The Future [Bethesda Magazine]
· Curbed's Prior Passive House Coverage [CDC]