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Old 06-18-2020, 07:38 AM   #1
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Insulation above garage (batt insulation question)


Going to take on the easy task of faced insulating the cavity area above my garage. I have some R30 insulation that is about 16 inches wide and need to install in 16 inch on center joists. With that being said, measuring most of the spaces between joists is anywhere from 14.5-15 inches or so.

Is it worth it to cut an inch off from the sides of the insulation before installing or is the compaction minimal to stuff between joists where it won't hurt the R value too much?

Total will be about 15 runs around 124 inches long with 48 inch length batts.

Thanks in advance!
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Old 06-18-2020, 07:44 AM   #2
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Re: Insulation above garage (batt insulation question)


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Originally Posted by theguy8969 View Post
Going to take on the easy task of faced insulating the cavity area above my garage. I have some R30 insulation that is about 16 inches wide and need to install in 16 inch on center joists. With that being said, measuring most of the spaces between joists is anywhere from 14.5-15 inches or so.

Is it worth it to cut an inch off from the sides of the insulation before installing or is the compaction minimal to stuff between joists where it won't hurt the R value too much?

Total will be about 15 runs around 124 inches long with 48 inch length batts.

Thanks in advance!
It is made with interference fit so it fills right tight to the edges, paper down.
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Old 06-18-2020, 07:45 AM   #3
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Re: Insulation above garage (batt insulation question)


No.

Compaction is fine.
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Old 06-18-2020, 07:51 AM   #4
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Re: Insulation above garage (batt insulation question)


First off, measure the distance between joists next to the walls. Your joists should be exactly 14 1/2" apart. In the middle of the span, they may vary if they have not been braced with anything.

You can brace them before you begin insulating in one of 2 ways.

1. lay a 2x4 on top of the joists, mark your 16" on center layout on that 2x4, then shoot it to each joist, moving the joist as needed before you fasten each one. (You obviously start at the exterior wall and keep your joists as straight as the wall is this way)

2. Cut blocking to fit between the joists to force them over. If you have some that are 15", you probably have some that are 14". By putting a row of blocking vetweemb the joists all the way across the ceiling, it braces the joists, straightens them out and spaces them evenly (assuming your blocks are all 14 1/2" long, and that it wasnt framed goofy to begin with).
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Old 06-18-2020, 08:06 AM   #5
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Re: Insulation above garage (batt insulation question)


Are you referring to the ceiling joists or the rafters all the way up directly below the roof?
Where are you in terms of climate?
Will you be adding drywall over the insulation?

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Old 06-18-2020, 08:16 AM   #6
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Re: Insulation above garage (batt insulation question)


Just wanted to clarify that the garage has already been sheet rocked and finished. There just isn't any insulation above in the "cavity area". This is for the ceiling joists and not the rafters. I'm located in Atlanta, GA
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Old 06-18-2020, 08:29 AM   #7
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Re: Insulation above garage (batt insulation question)


No need to cut it, it will lay in there just fine. Should really be unfaced then, imo.
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