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Community and Q&A

Insulate existing garage walls?

Mark_McFarlane | Posted in Energy Efficiency and Durability on

I have a house in Houston with drywall already installed on all 4 walls of a 2-car 22’*25′ garage. Two walls are shared with conditioned space and insulated. One SW facing wall has no insulation, and the NW facing wall is 90% insulated garage door, the remainder uninsulated.

The uninsulated SW wall (afternoon Texas sun) actually protrudes into the conditioned house, so only about 15′ are uninsulated. The garage ceiling is not currently insulated.

My goal is to make the garage a little cooler in the summer and a little warmer in the winter. I do not plan to add HVAC.

Adding insulation to the ceiling is obvious, the garage gets a lot of heat from the unconditioned attic through the uninsulated ceiling in the summer.

My question: is it worth tearing out the 15′ of drywall on the SW wall and insulating?. How much temp difference will it make inside the garage to insulate the 15′ of SW facing wall? Will it be a 1 degree difference, or a 5 degree difference?

I will do the work myself, and estimate about 2-3 days and a few hundred dollars to tear out the drywall, insulate, replace drywall and mud,.. Not a big cost or time sink, but if I’m only going to get 1-2 degrees of change in garage temp it probably isn’t worth the effort.

Thanks for considering this,


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  1. GBA Editor
    Martin Holladay | | #1

    I doubt whether you'll get a 5 degree difference by insulating one wall. I'm guessing that the temperature difference will be less than that.

    You can easily insulate these stud bays without removing the drywall. All you have to do is make a 4-inch-diameter hole in each stud bay. That will give you enough access to fill each stud bay with blown-in cellulose. Your local Home Depot or Lowe's will usually lend you an insulation blower at no charge, as long as you buy a few bales of cellulose from them.

    Once you are done insulating, you can patch the drywall holes.

    Here are links to two articles with more information:

    How to Install Cellulose Insulation

    Borrowing a Cellulose Blower From a Big Box Store

  2. Mark_McFarlane | | #2

    Thanks Martin.

    I forgot to add that the exterior walls are brick veneertyveksheathing2*4 studsdrywall.

    Your first article mentions that rental blowers are not sufficient for dense packed walls, but I guess in my application the horizontal density or long-term vertical settling won't be that big a loss, even 80% coverage will help.

    I'm also doing a home addition and figured I'd have the ceiling done in spray foam when that crew arrived in ~February, but if I rent a blower for the walls I can just blow the ceiling at the same time and get some advantage this winter (I'll be spending all day in the garage, as a temporary shop.) I just need to figure out an effect way to keep the insulation out of the vented eaves, short of building a bunch of dams. Rake,... plastic,...

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