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Building Envelope Tightness (BET) Test
Blower Door Test Failure and How to Pass

It’s harder to pass the blower door test with an existing home than it is a new one, but it’s not impossible.  The older the house is, the harder it is to pass blower door testing due to floor construction.

Before the current building code came out, a new house tested with ACHnat = 0.5.  In the Atlanta, GA area, that translates to ACH50 = ~12.  A turn of the century house has an ACH50 = ~30.  The difference is building materials and methods.

Newer Houses. New houses have the advantage of sealing holes in walls, floors, and ceiling throughout the building process.  With sheet goods, such as plywood and OSB, it’s easier to erect air barriers.

Older Houses. Older homes typically have 1x6 subflooring over basement or crawlspace.  To pass blower door testing, this is best handled by spray foaming the floor, either as a flash coat or as insulation.

Ideally, when an older home is improved, it’s worth contacting Home Insight early in the remodeling project to identify larger holes and find out how to fix them.  It’s worth running the blower door test before starting to help plan work.

Key Air Sealing Points. By the time of the final inspection, options are limited on how to improve blower door test performance, usually to the floor or attic.  There are a variety of types of holes to close shown in the Appendix A of Georgia's energy code: Air Sealing Key Points.  However, the house can be made tight enough to pass the blower door test unless there are serious holes in the walls and around windows.

When blower door testing fails, Home InSight tours the house with the client while the blower door fan is running to find holes.  We may use an infrared camera, if outdoor temperatures are hot or cold enough.  In our experience, the best sensors we have for finding air leaks are our eyes and hands.  We’ve evaluated enough homes to accurately predict air leaky locations.  Suggestions for improvement are made as we go.


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