Shorts-Attached Structures Outside the Air Control Layer and Blower Door Testing

Whether you are performing blower door testing or hiring someone to perform the test for you, it’s a good idea to understand how a home should be setup for the test.  Should a door be open or closed?  What can be sealed off?  How to address rooms attached to the house but are outside the air control layer?  That’s today’s topic, attached garages and three season porches.  How should those spaces be setup for a blower door test?

If the attached structure that is not the garage is fully conditioned and insulated, it may then be included with the envelope of the home and any door between the spaces should be open during testing.  Attached garages and three season porches, and other similar attached structures not designed to be conditioned by the home’s heating or cooling system need to be constructed in such a way they are kept outside the air control layer of the main home.  These spaces may be uninsulated, insulated and semi-conditioned, or in the case of a garage, may be fully conditioned, but should not be included in the portion of the home that is blower door tested.

How to set these spaces up for the test.  These spaces can act as a buffer zone for blower door testing.  Air needs to leak through these spaces first before reaching the air barrier of the home.  We really want to be testing the integrity and continuity of the air barrier without that buffer.  Because of that reason, garage doors (in the case of an attached garage) or an entry door or windows leading to the outside in three season porches or similar attached structures should be opened.  This gives any air unimpeded access to the house air control layer.

In the case of the attached garage, it’s important the air barrier be the tightest we can make it.   A car idling for just a few minutes inside a garage can create a spike of CO that ends up in the home.  We also store things in the garage we don’t want in the home.  We need to confirm through testing the garage is isolated from the home.  Garage doors up!

You don’t know unless you’re testing.

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