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Community and Q&A

How to insulate over sheetrock

Carole60 | Posted in Energy Efficiency and Durability on

I live in Arkansas and I am trying to convert my garage connected to my house into my painting studio.  The 2 outside walls are all ready sheetrocked but not insulated. I can not afford to have insulation blown in. I am a female 60 year old disabled vet.  I am looking for easiest and cheapest way to insulate the walls over the sheetrock.  Please help me figure this out.

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  1. Expert Member
    BILL WICHERS | | #1

    You could put up polyiso right over the existing drywall, but this will probably end up being considered living space where you would need to drywall over the rigid foam as a thermal barrier (or you can use plywood). 2" polyiso at R13 is a good minimum here, which will get you up to insulation levels a little better than a 2x4 studwall with batt insulation would be.

    That's probably the easiest way to insulate, but probably not the cheapest. It might actually be cheaper to just pull out the exiting drywall, put in batts (high density fiberglass batts will give you R15 in the stud bays), then put up new drywall. This is probably a little more work, but may well end up being cheaper if you can do all the drywall finishing yourself. Drywall luckily is one building material that has not massively increased in cost over the past two years.


  2. Robert Opaluch | | #2

    Another alternative: You could leave the drywall in place, and insulate inside of the stud bays with loose fill cellulose insulation. I'm assuming that you haven't done a lot of "do-it-yourself" construction work, your disability would not prevent you from doing this work yourself, with a helper, or a volunteer. The work usually could be done by one person, probably in a day or two, even if unfamiliar with this type of work.

    This would involve renting an insulation blower machine (sort of the reverse of a vacuum cleaner), cutting holes in the drywall, near the top of each stud bay in the exterior garage wall to be insulated (a couple inches from the top, every 16" or so along the wall between the studs, but below the wall top plates framing (top 3" of the wall), sticking the blower hose into the hole you cut, then dumping insulation into the blower machine, and running the machine to blow loose fill cellulose insulation into the stud cavity. You would need a step ladder to bring the hose to the top of the wall (for each stud bay). After filling up the stud cavities with insulation, later you need to patch the holes with drywall compound (sort of like soft putty) using a drywall knife (sort of a big, more flexible putty knife), and using some drywall tape or a drywall patch to help make covering the hole easier and get a better appearance. You might want to buy a $10 drywall knife/saw that would make cutting the holes easier, assuming you don't have a drill and hole driller bit the right size for the machine.

    Overall, relatively easy to do a decent job. Getting that last bit of insulation filled at the top of the stud wall would be helpful, but the job doesn't need to be perfect to be very effective at reducing heat loss through the wall.

    Once you get the hang of it after one or two stud bays, the work goes quickly.

    Example of loose fill insulation for sale:

    Example of tool rental to blow loose fill insulation into stud cavities:
    (Note that this deal gets you one free day of rental if you buy $300 worth of insulation (20 bags) but you probably don' need this much for the uninsulated exterior walls of an attached garage unless also doing the ceiling)

    Example of a drywall knife used to spread drywall compound to cover the hole:

    Not sure of your degree of disability, but to do the work solo, you would have to be able to bring a 165 lb blower machine from the rental location to your vehicle (likely they would do this for you), and from the vehicle into your garage. Hopefully you have someone to help if you need some assistance.
    According to the coverage and prices quoted in the insulation for sale, it would be a few hundred dollars to fill the exterior garage walls not shared with your home.

    You didn't mention insulating the garage attic. If the garage has a drywall ceiling then roof above it, you can blow insulation on top of the drywall ceiling, using the same blower and insulation. Even easier since no cutting and filling holes, assuming you have attic access from somewhere.

    Bill mentioned polyiso insulation board. Its VERY lightweight, comes in 4x8 sheets (options from 1/2" to 2" thick), so would install quickly and easily. Some are faced with foil, which would increase the effective insulation value, by reflecting heat. If you can get Thermax polyiso, it can be installed and not covered, since it is more fire resistant than standard polyiso. Assuming you can get these 4'x8' sheets delivered, the installation work would go very quickly and easily.

    You also could consider both filling stud wall cavities with insulation, and adding polyiso board insulation on the interior of the wall. You just have to be sure that your exterior siding/cladding allows water vapor to pass through it. No poly plastic sheeting in the wall. Otherwise you might end up with condensation, wood rot or mold problems. Polyiso does come with other facers other than foil to avoid this problem, but foil will not allow water vapor to pass through. It can be a problem in the humid South.

    Reducing the air leakage around the edges of your garage door also might be something to consider. Draft stopper tubes can be used at the bottom of the door. Many people remove the garage door altogether to renovate it into a continuous wall with a window or weatherstripped 3' wide x 6'8" exterior door. This seems like more work than you would consider. But covering the garage door might be something to consider if insulating the walls doesn't provide enough comfort in your garage space. Carpet on the garage floor might also help provide some insulation and protection from a colder concrete slab floor of a garage.

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