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Community and Q&A

Blown Insulation

John Roy | Posted in Building Code Questions on

Hello, we have a bonus room over the garage that does not have an attic. The ceiling of the bonus room is drywall, studs, then roof. The ceiling goes to an angle, then across to the other angle to create a ceiling that looks like the letter “A”. I took out the middle line of the “A” and noticed the insulation had been tamped down by a previous owner’s rodent problem. I am wanting to blow in insulation between the ceiling and the roof in between the studs, but I am not sure if I will have a moisture problem. Is blown in insulation the way to go? If not, what would be the best way to insulate? Thanks, John

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  1. Expert Member
    Dana Dorsett | | #1

    Code generally requires that there be a ventilated 1" minimum gap between fiber insulation and the roof deck. But if dense-packed (3lbs per cubic foot minimum if celluose, 1.8lbs if fiberglass) it can be relatively safe in US climate zones 1 & 2.

    The best way to insulate an unvented roof is to add the code requisite amount of insulation above the roof deck prior to adding any fiber insulation between the rafters. The particulars are both climate and construction specific.

    How deep are the rafters?

    Where are you located?

  2. John Roy | | #2

    The rafters are 4 inch studs, but there is gap where the two sides meet. There wasn't any insulation in that area, just along the roof. we are located 20 miles north of Atlanta. I will try to add a picture.

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