Williamstown Residence “by far the tightest I’ve tested”, says CET analyst.

On March 1, 2007, the Center for Ecological Technology conducted a blower door test on a Williamstown house—now nearing completion—confirming its status as one of the tightest homes in Massachusetts.

The Owners, with Bruce Coldham, AIA and Builder Steve Haskins (Haskins Construction) set out to create a Zero (Net) Energy Home which could generate in a year as much energy as it consumes. Such a project requires tight control of the energy budget and attention to many diverse facets of design and construction—including the air-sealing of the building’s shell. On paper, Coldham designed an envelope that allowed very low rates of air infiltration, but the proof is often in the testing.

CET’s Blower Door Test rates Air Changes per Hour (ACH) at a standard pressure difference of 50 Pascals between inside and out. Energy Star for Home’s threshold is 5 ACH 50 or less.

Last Tuesday’s test results confirm the careful attention paid by builders and designers alike. The Williamstown home was tested at .96 ACH 50—more than 5 times tighter than currently required for Energy Star residential certification.

Another common measurement is the Equivalent Leakage Area (ELA)-100, which gives a leakage rating per 100 sq. ft. of shell. New construction without special attention to air sealing normally reaches an ELA of 4 or more; an Energy Star Home requires an ELA of less than 2. The Williamstown home achieved an ELA of .41--total leakage equal to less than half an inch per hundred square feet of shell.