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Insulation type for garage attic with Ridge Vent and Soffits

Hello All,

I have an attached 2 car garage that has it's own roof in the Dallas, TX area. The garage is finished with sheet rocked/dry walled walls and ceiling. The attic space above does not have any insulation (not on the floor or the rafters). The roof is composite shingles with a ridge vent and a few soffits on each side. The attic space shares a portion of the home's exterior wall of a bathroom and a bedroom (this wall currently has fiberglass insulation with some areas not covered well).

We do have exposed PVC drain pipes (toilet and tub) from the bathroom that come into the attic space.

There are no plans to convert this attic space to a livable space.

Should I at least get the shared wall spray foamed?

What would be the best insulation option for the rest of the attic space?

Thank you for your suggestions,


Asked by dapakattack
Posted Jan 3, 2018 12:21 PM ET


4 Answers

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You should caulk or foam any openings, such as those around the vent pipes. Air sealing is the biggest bang for the buck. See this article for additional details: http://www.greenbuildingadvisor.com/blogs/dept/musings/getting-biggest-b...

Answered by Steve Knapp CZ 3A Georgia
Posted Jan 3, 2018 12:34 PM ET


It's important to air seal and insulate the wall between the garage attic and the bathroom and bedroom. If the wall is insulated with fiberglass batts, you shouldn't see any insulation -- instead the insulation should be covered with drywall (which acts as an air barrier).

1. If you know that there are insulation voids, fill these voids with insulation.

2. If you can see any air leaks, seal the leaks.

3. If drywall is lacking, install drywall. Even better: First install a continuous layer of rigid foam, and then cover the rigid foam with drywall. All this work should be performed with attention to airtightness.

Answered by Martin Holladay
Posted Jan 3, 2018 1:10 PM ET


Thank you Steve and Martin for your replies.

Martin, I wouldn't have thought of installing drywall after foaming that wall. I would have thought that the foam or other insulation would be all one needs.
What about the rest of the garage attic? Should I foam the rafters or the floor or do cellulose/fiberglass on the floor? (Remember the soffits and ridge vent).

Answered by dapakattack
Posted Jan 3, 2018 2:38 PM ET


Fluffy insulation like fiberglass definitely needs an air barrier on both sides of the wall, and taped drywall works as an air barrier.

If you fill the studs with spray foam, the spray foam acts as an air barrier. But the exposed spray foam is somewhat of a fire hazard. Code officials differ in their interpretation of code requirements for covering spray foam, especially if the spray foam faces an attic. Many code officials would say that spray foam facing an attic doesn't need to be covered. But some others will rule that the spray foam needs to be covered with 1/2-inch drywall for fire safety.

There is no need for you to insulate your garage unless you intend to condition it (heat it in winter or air condition it in summer).

Answered by Martin Holladay
Posted Jan 3, 2018 3:06 PM ET

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