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What Insulation should I use in between Metal Studs?

Masb | Posted in General Questions on

We’re using metal studs to finish our basement and the studs are only 2.5 in wide. Fiberglass batt insulation is 3.5 in wide, so they won’t fit. What insulation should our contractor use that will fit and not be too expensive?

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  1. Walter Ahlgrim | | #1

    Please understand that the metal studs conduct heat so well insulation in between is close to useless for thermal purposes it will deaden some sound transfer.

    With steel construction all insulation must be external to the structure.

    Please make some time and watch a few Dr Joe Lstiburek videos He has said you are trying to eat your sweater and stuff it between your ribs. Your sweater would work much better if you just wrapped it around yourself.


  2. Expert Member
    Zephyr7 | | #2

    The best option is to use rigid foam on the exterior side of the studs, which avoids the thermal bridging issue completely. If you're putting in batts for sound control, use the "sound control" variant of mineral wool for 2x4 walls, which is about 3" thick (the sound control variant is less than then usual 3-1/2" thicknesS), then squish it a bit. It would probably be easier, and certainly cheaper, to squish R11 fiberglass batts into the narrower space though.


  3. Expert Member
    Akos | | #3

    Just to make sure, behind the steel studs there is a layer of rigid insulation on the basement wall. If not, this needs to be fixed, in a lot of cases basements insulated with batts only end up a mouldy mess.

    For the steel studs, you can use almost any cheap insulation you can find. 3.5" R11 fiberglass batts easily squish to 2.5, you can also get R8 attic rolls.

    The steel studs are a thermal bridge, but adding insulation to the cavity does still increase the assembly R value, as long the insulation you are putting in there is cheap, you should always fill the cavity.

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