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Is it worth it to insulate the roof on a detached garage?

Is it worth it to insulate the roof on a detached garage?


Old 01-26-13, 01:18 PM
Thread Starter
Join Date: Dec 2012
Location: USA
Posts: 133
Is it worth it to insulate the roof on a detached garage?

I just recently bought a house that has a large 1 car detached garage. It has block walls (covered with vinyl siding) with wood roof trusses (16" OC) and an asphalt shingle roof. I don't believe it has any kind of venting at the roof ridge, but it has attic-style vents in both gables. Not sure if it has soffit vents or not.

I don't know about the block itself, but as far as I can tell the structure is completely uninsulated.

When I first looked at the house it was around 80 degrees outside and it was very hot inside the garage, due to the uninsulated roof.

Would it be worth it to install some insulation in the rafters to keep out some of that radiant heat? And if so, what's the best to use and the best way to do it? It looks difficult to get at the rafters due to the 16" spacing, that's why I ask. I'm a little wider than 16" I think
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Old 01-26-13, 02:00 PM
XSleeper's Avatar
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Join Date: Dec 2004
Location: USA
Posts: 20,516
Fiberglass insulation does not keep out radiant heat. Best way to cool off a garage is to open the garage doors. You'd probably be better off if you sheeted the ceiling joists with OSB or drywall to put up an air barrier between the attic and the garage space. There's no point in adding insulation to an unheated/non-air conditioned space.

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