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H2O Engr 10-01-2010 06:04 AM

Garage Attic Insulation Questions
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Background: Need to insulate attic above attached garage which has finished drywall ceiling. Construction is 2x4 roof trusses 24" OC. Fiberglass R-13 faced insulation has been purchased. Will place 4x8 sheets of plywood atop bottom chord of trusses and use as flooring for storage.

Issue: There are multiple electrical outlets installed in the garage ceiling for lights, etc. and there is 2x4 blocking running between the trusses to which the receptacles are attached (pictured).

Question: Do I place the insulation faced-side down? How do I continue the insulation across the blocking for the outlets? Just slit the paper and pull the insulation apart at those locations or should I actually cut all the way through and use separate pieces in between them? The intent is for the insulation to not stick up above the trusses since flooring will be installed.

FYI - the white cable has been abandoned and removed since the picture was taken. Notice it crossing over the truss. My new wiring is all up to code.

bob22 10-01-2010 06:42 AM

In my opinion you should not be using this space for storage of anything of significant weight. That ceiling is designed to hold up the drywall ceiling and is not engineered for storage. The insulation could be split where needed; are you heating the garage space? Typically, the paper side of insulation goes to the warm in winter side of the wall/ceiling.

H2O Engr 10-01-2010 08:20 AM

The additional weight is a good point and I am glad it was mentioned. I agree, storing engine blocks and transmissions in the attic is out of the question. It will be used for *light* storage and will try to place items near the load-bearing walls. 4 sheets of 4x8 OSB were used as flooring, so they will remain in addition to the 8 hollow core interior door slabs that were up there to distribute stored items load across a few trusses. How much weight is too much for an *average* truss system?

Garage will be heated. Think it is better to notch the insulation around the the outlets and blocking than to compress it.

Michael Thomas 10-01-2010 09:00 AM

If the garage is heated, the vapor retarder goes toward the drywall below the trusses.

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