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Community and Q&A

Insulation over drywall?

Nancy Wall | Posted in General Questions on

I have a garage that has drywall on the walls but is not insulated. I cannot afford to take down the drywall, insulate and replace the drywall. Im told that blown in insulation is not an option. The front of the garage gets full morning sun. My question…please don’t laugh too hard… can a foil insulation be put directly over the drywall. I know it might not look the best but it is so hot in there. The garage door is insulated.

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  1. Steve Knapp CZ 3A Georgia | | #1

    Tell us where you live since climate is a factor. Why is blown in insulation not possible?

    And are you referring to foil-faced rigid insulation or something else? Are you using the garage as a work space or just concerned about heat build up when the door is closed?

  2. Nancy Wall | | #2

    Thanks for your reply. I live in upstate South Carolina. Not sure why we can't do blown in insulation , just told not. I am using the garage as a studio work space. There are no windows or other doors in the garage. I was thinking of the sheet/roll
    bubble foil or something like that using staples to attach. I would need to do it myself

  3. C L | | #3

    Suggest you get another evaluation to determine why blow in insulation is not an option.

  4. GBA Editor
    Martin Holladay | | #4

    I'm guessing, but it's possible that your garage has no wall sheathing -- just siding installed against the studs. If that's the case, it may explain why insulation contractors are reluctant to recommend blown-in insulation.

    It's certainly possible to install insulation on the interior side of your wall, it that's what you want to do. I would recommend some type of rigid foam insulation -- the thicker, the better. (Two inches would be good.) You would also need to install a layer of drywall on the interior side of the rigid foam as a so-called thermal barrier or ignition barrier (to reduce the fire hazard).

    Bubble wrap is basically useless as an insulation. You might want to read this article: Stay Away from Foil-Faced Bubble Wrap.

  5. Steve Knapp CZ 3A Georgia | | #5

    Nancy. Are you looking for a temporary solution or a way to convert the garage to permanent indoor space? Do you have any appliances such as a gas water heater in the garage?

    If you want a temporary way to use the garage as a workspace, you might consider buying a portable AC unit such as this:

    If you are thinking about converting the garage to indoor space, that is a much more complicated proposition.

  6. Nancy Wall | | #6

    I do have a gas hot water heater in the garage. I am using the garage for making pottery but am not going to convert it to permanent living space. I still put my car in the garage sometimes. I just need the space to be usable in hot weather. I think the space is too hot for a portable a/c without some type of insulation or heat barrier. Thank you for your reply. Any suggestions are so appreciated.

  7. Charlie Sullivan | | #7

    If you want a really low-cost solution that will just take a wee bit of the edge off the heat gain, radiant barrier foil does provide a little bit of benefit. Regulars here at GBA all despise it, because it's usually overpriced and sold with amazingly misleading advertising. But it might make a just noticeable difference on an otherwise uninsulated wall. It might cut the heat flow through your uninsulated wall but 25% (very rough guess), but it might improve the comfort inside a little better than that would indicate if you are near the wall, because it would decrease the effect of that wall surface on the "mean radiant temperature" you feel inside.

    Aside from the need to hold your nose and buy it from unscrupulous hucksters, the limited benefit it would offer, and the unusual aesthetics of a shiny silver interior wall surface, the other drawback to be aware of is that if you air conditioned the space inside, and the foil was air tight, you'd have the potential for moisture coming from the humid outside air to condense on the drywall side of the foil. That problem could be avoided for the most part by buying a perforated version of the foil, designed specifically to avoid that problem. Both for that issue and for the thermal performance, it would be ideal to suspend the foil 3/4 inch or so away from the wall, but with all four edges taped to stop air flow around it. Here's one example, which is, like all the others I know of, made by a company that specializes in misleading advertisements.

    I expect that others will chime in shortly, scolding me for encouraging the use of a mostly-discredited material. It's nowhere near as good as real insulation, but as Martin points out, the real insulation would require drywall over it, and if that's outside your budget and you want something you can try for perhaps just $100, there is a slight benefit.

    For $100 you can also buy a modest size cooler and a large supply of beverages to keep in it, and still have money to freeze some ice to keep them cool. I'm not making any claims that the radiant barrier would be any more effective than that.

  8. GBA Editor
    Martin Holladay | | #8

    I don't disagree with anything you wrote. Radiant barriers have their uses. They aren't insulation, but they are relatively cheap, and in this case a radiant barrier might help.

  9. Nancy Wall | | #9

    Thank you so much...I have learned a lot and know what to look out for. Now the shopping begins. Great site! The cooler sounds good too.

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