Tightening up to Zero: the Blower Door test Blowout!

Creating a tight envelope is a critical goal in shooting for a zero energy home. And it is not enough to simply apply the correct techniques and materials, it is essential that we have a measure of their effectiveness. This is where the blower door test comes in. A blower door test is a diagnostic tool designed to test the air tightness of buildings.

A blower-door fan is sealed into an exterior doorway, all the house vents are temporarily sealed, and the calibrated fan blows air out of the house creating a pressure difference between the inside and outside, which draws air into all of the inadequately sealed cracks, holes and penetrations. A pressure sensing device is used to measure the rate of pressure change/leakage. The data is entered into a standardized formula and the number of Natural Air Changes per Hour (NACH) is derived. Typical production-built homes built under current building codes will score at about 0.5NACH or higher (one complete air change every two hours). A well built, near zero energy home aims for a score of 0.1-0.2NACH. EarthCraft Virginia officials, including Chuk Bowles, Technical Director (tending to the pressure monitor above) and KC McGurren, Executive Director, supervised the testing of our home this week.

As KC is indicating in the picture, the results were encouraging! We registered a score of 0.16NACH, reflecting approximately one complete air change every 6 hours, approximately 3 times tighter than a well built new conventional home! Mark Waring, our builder, said that he was very pleased with this performance, which reflects the tightest home he has built to date. This tightness will minimize the heating/cooling load, reducing the demand on the geothermal system and putting less draw on the solar PV array.

ZEH Virginia, its all in the little things

Building a green ZEH is not one big thing, but a series of many little things. Our builder is using AdvanTech subflooring, a product offered by Huber with a 50 year guarantee that shows significant improvement over both OSB and plywood in stiffness, strength and water resistance, while using no added formaldehyde and meeting the Sustainable Forestry Initiative (SFI) Standard. This produces stiffer, quieter floors while minimizing outgassing. The piece of light blue material you see sticking out from the block in the lower picture is a foam gasket that serves as an air sealing measure along the uneven block and brick. It also is a moisture break to keep water from migrating to the wood from the foundation. The aim of maintaining an extremely tight "envelope" with respect air and moisture infiltration is a guiding principle that directs innumerable building product choices and practices when constructing a zero energy home. Mark, our builder, is shooting for the lowest HERS rating house in Virginia, so each of these decisions is made with efficiency and best practice in mind.