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Community and Q&A

Garage wall insulation

geran_brown | Posted in General Questions on
I was wondering if I could get some advise on the best way to insulate my garage walls. The walls are cinder block with a brick exterior. The whole garage would not be conditioned, I will however have a server room (5×7) that will be conditioned either passively or with its own heating/cooling unit contained within the room.
Outside wall
Wall connected to house
I live in the Washington, DC metro area (zone 4A not marine).
Any help would be greatly appreciated!

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  1. Expert Member
    BILL WICHERS | | #1

    I’d use polyiso on the inside of those walls, and drywall over it as a tight sandwich. This is most space efficient and I’m assuming easier than putting the insulation on the outside.

    Note that you won’t need to heat that room if you have any real amount of equipment in there (over maybe 500 watts worth). You will need cooling though. A minisplit system is the usual way to cool a small server or network room, since the indoor unit can be easily wall mounted and the outdoor units are pretty small.

    Now something for you to consider: My primary buisness is designing, and sometimes managing under contract, large telecom facilities and datacenters. We never heat the equipment areas, we only cool these areas — and the cooling runs year round. The big thing to think about is the electrical costs to operate the sites, which are BY FAR the largest operating expenses for these facilities. A typical ~50,000 square foot facility will usually be around $400,000/month in electricity alone. And that’s on lower industrial electric rates than you can get for residential service.

    I mention this because it’s often cheaper to lease colocation space in a large facility than it is to host things at home. I’ve had customers before tell me the savings in their electric bill at home was more than the cost of the colocation service, and the colo facilities have better network connections too. There are a number of such facilities on the Virginia side of the river in your area. I’ve worked in many of them.


    1. geran_brown | | #2

      Thank you for the reply Bill.

      So you say polyiso on the inside of the walls...would 1.5" or 2" be best? I'm leaning towards 2" (roughly R-13) to give me a continuous mass wall so I wouldn't have to put extra insulation on the inside. I would like to keep studs (laid on their face) to have some mounting points for electrical outlets/switches. You are correct, I can't easily put insulation on the outside since it is brick.

      Heating the room wasn't really a concern since the garage temperature currently never drops below 40/50F. Cooling on the other hand was something I was going to do for sure. Passively, I have two windows in the room for the server that I was going to set it up to cycle air in the room to hopefully get 1ACH. I've seen it done but maybe that was on the inside of a house...I'll have to review that again.

      Thank you for the suggestions of colocation and everything. I looked into those in Maryland (where I'm located) and VA. Due to me having solar for my home with the grid being the backup, my energy bills aren't that high. My electricity rate is $.07 currently and I really only pay for it electricity during the winter when the sun isn't out as long. If I find out my bills are getting to the point that colocation make more sense I will look into it more.

      1. Expert Member
        BILL WICHERS | | #3

        1.5” polyiso has the advantage of being the same thickness as the studs. It isn’t really enough though. If you go with 2” thick polyiso, you’ll need to add 1/2” plywood to the studs to get them up to the same depth as the polyiso.

        Another, potentially better, option is to put 1/2” continuous polyiso insulation up first, then put up the studs and 1.5” polyiso between the studs. This avoids the need for plywood and gives you thermal breaks on the studs. This is probably how I’d do it myself.

        I’m pretty familiar with your area as I’ve been out there for contracts many times. Many, many commutes on the BW parkway between Baltimore and DC. I miss nick’s fish house and cream of crab soup :-) I haven’t been out there in maybe two years. Time to go visit friends again soon I think...


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