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We would like to insulate and drywall the garage ceiling to work on projects in the cold winter and hot summer. (We'll probably install a mini-split or something similar, too.) This question is specifically about the ceiling (but see this question about the walls).

This reference says we need to target R38-R60 in Zone 4 for an attic space...but the garage is not an attic. In addition, the rafters (pictured below) are 2x6's on 24" centers so R23 is about the most we could get in with batts.

Question: What is the best practice to insulate (and drywall) the ceiling in situations like this?

Attic insulation zones

Picture of the garage rafters:

Garage rafters

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  • The garage is not living space. Those those R-value recommendations can be relaxed. But the greater the R-value of the insulation, the easier it will be to heat and cool.
    – SteveSh
    Sep 2, 2022 at 23:03
  • How often do you plan on using the garage to work on those projects you mentioned?
    – SteveSh
    Sep 2, 2022 at 23:04
  • And are you talking about insulating against the roof itself - the rafters (generally not recommended) - or using the horizontal ceiling joists?
    – SteveSh
    Sep 2, 2022 at 23:17
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    The grarge framing in your picture is barely adequate to hold the roof up, and almost certainly will not hold up drywall and insulation without considerable re-engineering/rebuilding. This is common for lightly-built garages - the collar ties can hold the roof from spreading, but have no spare load capacity, particularly being spaced every other rafter.
    – Ecnerwal
    Sep 2, 2022 at 23:51

1 Answer 1

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You have 5 1/4 inch hight at the 2x6.

So here is what you can do choosing different materials.

Rigid foam's have better R than Fiber glass, but they cost more.

Now the choice is yours if you want to reach >40 R value.

foam

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  • OP talked about having 2x6's.
    – SteveSh
    Sep 2, 2022 at 23:18
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    @SteveSh, a 2x6 is dimensionally 1.5 x 5.5" so I think \@Ruskes threw away a 1/4" for estimation or maybe had a typo? Anyway, do you really think it deserves a DV?
    – KJ7LNW
    Sep 3, 2022 at 6:34
  • I didn't down vote, at least I don't think I did. And my comment was from Ruskes original answer, before editing, where he said a "3-1/2 inch height at the 2x4."
    – SteveSh
    Sep 3, 2022 at 12:15

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