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Advice on my wall build?

rileyg | Posted in GBA Pro Help on

Hi Ladies & Gentlemen
This is my first time for posting a question, but I have been creeping around on here for a couple years. I am just looking for affirmation or not if I have the right combination for my workshop walls that I am planning on building. I have read lots on air sealing and vapour barriers etc. but have never really found my exact situation.

in floor radiant heating
climate zone 6 interior BC

1/2″ plywood or osb with latex paint
6mil polyethylene vapor barrier
R22 MW
2″x 6″ wood studs on 16″ centers
1/2″ plywood sheathing
Tyvek WRB
1.5″ comfortboard 80 (cannot afford 3″ which is why I think I need the 6mil poly on the interior)
treated 1″ x4″ horizontal strapping bevelled on top to help with drainage
Vertical metal cladding
venting & bugscreen top & bottom

Thanks in advance for the advice.

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  1. Expert Member
    Akos | | #1


    The exterior strapping should not be pressure treated if you are using metal cladding (will lead to corrosion where they touch). Also don't forget the pick your air barrier location, just as important as the insulation. Exterior plywood is probably the least likely place to get damaged and banged up in a workshop.


    P.S. One piece of advice on radiant floor. It is very slow to react. Depending on the usage having to wait for 2 to 3 hours for the shop to come up to temperature might not work.

    1. Expert Member
      MALCOLM TAYLOR | | #3

      I don't know how common this is down there, but many lumberyards here in Canada have now switched from the corrosive ACQ treated-wood to MPS, which doesn't affect fasteners or metal cladding.

  2. Expert Member
    Dana Dorsett | | #2

    That stackup should be fine.

    Using a smart vapor retarder in lieu of the 6 mil polyethylene would improve the overall drying capacity of the assembly. Going with 2-mil nylon as the vapor retarder is not a big upcharge (about 2x the material cost of polyethylene, same labor.) If it's a workshop with only intermittent use and no interior moisture sources it might not need anything other than interior latex paint for vapor retarder, but that's probably harder to sell to the inspectors.

  3. rileyg | | #4

    Some good advice here. It's a garage/workshop so there will end up being some moisture coming in on vehicles. I plan on keeping the temperature around 14c/57F which should be comfortable in the colder months.

  4. GBA Editor
    Martin Holladay | | #5

    I'm going to guess that "MW" stands for "mineral wool."

    Your interior layer of plywood or OSB (with a layer of latex paint) is already a smart vapor retarder. So you don't need interior polyethylene, and you don't need to spend any money for an additional smart vapor retarder.

    Just make sure that you install your interior layer of plywood or OSB in an airtight manner -- because attention to airtightness is always good.

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