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Building Science

Air Sealing the Ceiling Joists in an Attached Garage

A little forethought makes it a lot easier

Garage ceiling joists present a challenge for creating a continuous air barrier and keeping bad air out of the house. This builder made their job even harder by not considering this in the design phase.
Image Credit: Energy Vanguard

The I-joists in the lead photo here run across the top of the wall between the dining room and the attached garage in this home under construction in the Atlanta area. In the old days, before anyone worried about air moving through those joist cavities, the builder didn’t bother to do anything beyond securing the joists.

You can see here, though, that the builder of this home knows a thing or two about air sealing because they’ve put blocking between the joists. But what do they do next?

Why do these joists need to be sealed?

Three little letters are all you need to know: IAQ. Homes with attached garages often have worse indoor air quality than homes without attached garages. When is the last time you walked into a garage and thought to yourself something like this: “I love the smell of this garage! I could stay out here all day just breathing in this wonderful air!”

I don’t recall ever having had that thought. But I do remember the experience of trying to get through someone’s smelly garage as quickly as possible and wishing I had a respirator. That’s because of all the nasty stuff we keep in our garages. And that air is not something we want in the house — so let’s keep it out in the garage.

That’s where air sealing comes in. We want the most robust air barrier possible separating the living space from the garage. The joists that run across the top of the wall separating the garage from the house must be sealed. That’s where the air barrier should be — not at the drywall in the garage. And the air barrier at the joists consists of two parts: blocking to fill the…

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