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Community and Q&A

What type of insulation and how much insulation should I use between ceiling joists in garage?

jddeCastro | Posted in Energy Efficiency and Durability on

I live in zone 5 in northern New Mexico and live in an apartment above a 3 bay garage. The ceiling joists in the garage are 2×12 on 12″ c/c. The only heat source for the upstairs is from a small wood stove. I need to insulate the ceiling of the garage below. The garage walls have no insulation. What type of insulation and how much insulation should I use between ceiling joists in garage? Also I would need to insulate the rim joists.

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  1. GBA Editor
    Martin Holladay | | #1

    According to the 2009 Intenational Residential Code, the minimum R-value for floors in Climate Zone 5 is R-30.

    Here's an article that tells you everything you need to know about insulating the ceiling of a garage (in other words, the floor of an apartment over a garage): How to Insulate a Cold Floor

  2. jddeCastro | | #2

    Thanks for the information. I can work from the pdf file you sent. It seems that I need to learn to spray foam insulation.

  3. GBA Editor
    Martin Holladay | | #3

    It's best to leave the installation of spray foam to a trained contractor. It usually isn't a do-it-yourself job.

  4. Expert Member
    Dana Dorsett | | #4

    With 2x12 running 12" o.c., with blocking and rim joists you're looking at something like a 20% framing faction, so even a full cavity fill of cellulose won't quite hit the same whole-assembly R of R30 in 16" o.c. joists. The rigid foam below is critical to making it a true high-performance assembly.

    Doing a flash-inch of closed cell foam for air-sealing can be a DIY project with a 600 board-foot Tiger-Foam/Fomo-Foam etc kit. Doing a full cavity fill of open cell foam is definitely not DIY territory, and may be cheaper in the end than a flash'n'fill with dense-packed cellulose. (The high expansion of open cell makes for a tighter assembly than you'd get with a flash-inch approach too.)

  5. jddeCastro | | #5

    Okay. Thanks for the heads on on spray foam insulation.

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