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Community and Q&A

Exterior wall insulation doesn’t seem to work

seangaug | Posted in Energy Efficiency and Durability on

Climate zone: 3b (Northeast BC, Canada)

I am renovating a rancher built in the ’50s. This house didn’t have any wall insulation originally. 2X4 construction. I have started at one end of the house and rebuilt a couple of the exterior walls and re-sheathed.

The new walls from outside in:
1″ cedar plank siding
1X4 furring strips
2″ XPS foam R10
1″ XPS foam R5
WRB house wrap
1/2″ OSB sheathing
2X4 stud wall
Rockwool Comfortbatt R14
5/8″ drywall
latex paint and primer

My understanding from reading up on exterior insulation was I shouldn’t use a vapour barrier on the inside as this would cause condensation build up between the walls. With the majority of the insulation being on the outside and no vapour barrier inside the walls should dry to the inside. Did I get this right? The room doesn’t feel as warm as I had expected. Could just be me.

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  1. Expert Member
    AKOS TOTH | | #1

    Lot of perceived room comfort comes from warmer floors. If the house is over something like a crawlspace or basement with no insulation, the floor will be fairly cold making the room itself feel uncomfortable.

    Also, no amount of insulation will make up for a leaky assembly. If the house (floors, walls, roof) are not well sealed, you can be loosing more heat through air leaks than through the lack of insulation of the old walls.

    The 3B is your plant climate zone, my guess you are in climate zone 6 (4000 to 5000 HDD Celsius).

    In terms of the vapour barrier, you are correct, with that much insulation on the outside, you don't need one.

  2. seangaug | | #2

    Thanks for replying to my query.

    There are many areas of the home that still require updating and there are many air leaks that still need to be fixed. I'm glad to read that the ratio of exterior:interior insulation is sufficient to not require the vapour barrier.

    I'll continue with the renovations and I look forward to warmer results.

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