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Community and Q&A

Insulating garage ceiling below bedrooms

mike93lx | Posted in Energy Efficiency and Durability on

Hi everyone, I have a split ranch with a 2-car garage under the bedrooms. The back wall of the garage is completely below grade, the left wall is half below grade (slope), the right wall connects to the 1st floor and the front wall has two 8×7 insulated doors. There are no windows, the joists are 9″ tall, and I am in Massachusetts.

The ceiling is currently drywalled and i could see some R-9 batts through a gap.

The bedroom floors, particularly at the front of the house, get quite cold in the winter.

I intend to remove the ceiling to address sheetrock issues, some wiring and insulation. My goals are to keep the bedrooms floors warmer, add some sound dampening between the floors, and increase fire resistance to the rest of the house. I know type-x is the code-requirement for fire control, but as we park in the garage and my kids’ bedrooms are above, I really want to do everything I can there.

I was thinking about 3″ of closed cell for thermal and then a layer of rockwool for sound and fire, all sealed up by 5/8″ Type-X. My hesitation is that this will be fairly expensive, as the garage is about 650 sq ft (I was told $1/board foot for closed cell, so this would be $2k to spray), plus $700 for the rockwool. I would DIY everything but the spray foam.

Is this the right way to go or should I do something else?


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  1. GBA Editor
    Martin Holladay | | #1

    Here is a link to an article that gives advice on this issue:
    How to Insulate a Cold Floor.

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