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Community and Q&A

What cold wall/vapor profile system is practical to use in Whitehorse, Yukon?

1cornerstone | Posted in GBA Pro Help on

Dear Sirs
Would you please guide me in understandingthe design for our new house ?
We live in Whitehorse,Yukon Territory, so our goal is super insulated, because
of our cold climate.

While Yukon is mostly a Subarctic/Arctic region, Whitehorse is much milder than the interior Yukon.
For example:
Average January temperature
Whitehorse -17.7C Old Crow -31.1
(the record daily low was -52.2 in 1947)
Average July temperature
Whitehorse +14.1C Old Crow +14.6C

I understand interior vapor barrier is appropriate only for severe cold climates, because the wall system must cope with substantial moisture drive from the building interior and into the building envelope during the heating season. Does Whitehorse fall within that parameter and require a interior Class 1 poly barrier?

Different super-insulated homes have started to appear in Whitehorse, double walled cellulose packed, even triple walled batt packed, but they all have interior poly in common.

If appropriate, I would like to utilize a wall system featured in the following article (with the addition of an interior 2×3 horizontal strapped insulated chase wall).

Figure 8: Frame Wall With Exterior Rigid Insulation With Cavity Insulation and Brick or Stone Veneer

Understanding Vapor Barriers/2006-10-24 (rev. April 2011)by Joseph Lstiburek

If this wall system/ vapor profile isn’t entirely appropriate, would you kindly help me understand it’s shortcoming for the Whitehorse climate, and what would be more suitable?

Brick veneer/cedar siding
Drained cavity
Exterior rigid insulation (EPS?)
Membrane/air-barrier/drainage plain
Plywood or OSB
insulated 6″ wood wall
2×3 wood horizontal strapped insulated chase wall
vapor semi-permeable paint

D’Arcy Olynyk

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  1. user-1140531 | | #1

    As mentioned in the article, the R-value of the foam needs to be high enough to prevent its interior side from falling below the dew point temperature. Maybe someone here can tell you how many inches of foam would be required. I believe the main insulation layer would also play a role in the temperature of the interior side of the foam.

  2. user-757117 | | #2

    An old rule of thumb for cold climates and roughing out how much insulation to put where is to put 2/3 of the R value on the exterior side of the sheathing - for your climate, you may want to consider putting 3/4 of the R value to the exterior side of the sheathing.
    The idea is to make sure that there is enough insulation on the exterior side of the sheathing to keep it warm - warm enough that any water vapour that reaches the sheathing will not condense there and wet the framing.
    It is worth mentioning that even in your climate air transport of moisture will pose a larger risk than will vapour diffusion so a very high quality air barrier system should be a priority.
    If the air barrier system must include poly (to mitigate vapour diffusion) then so be it, but for poly to be an effective air barrier over the life of the structure it should be located so that it is well supported and protected from damage.

    There is also a possible liability in using poly on the interior and thick rigid foam on the exterior.
    If moisture ever does get into your walls, it will have a very difficult time drying out - if it ever does.
    This is the dreaded "double vapour barrier" or "moisture sandwich".

    Though it is certainly possible to build a home using exterior foam sheathing in your climate, personally I would check out some other options first.
    Stick-built "double wall" homes can be advantageous in very cold environments because the thickness of the walls is often scalable and in some cases create an opportunity to move the sheathing further towards the interior (where it will be warm) without having to get into some tricky and not-so-user friendly details associated with very thick exterior rigid foam.

    Here is a link to a recent Q&A thread along similar lines that you might find useful:

    Also for your perusal:

  3. user-757117 | | #3

    Can someone please dial back the sensitivity of the spam filter?

  4. GBA Editor
    Martin Holladay | | #4

    If you choose a wall assembly without any exterior rigid foam, then you should (in your climate) definitely include interior polyethylene.

    If, on the other hand, you decide to install exterior foam, then you shouldn't include any interior polyethylene. To understand why, read this: Calculating the Minimum Thickness of Rigid Foam Sheathing.

    If you decide to install exterior rigid foam, you must be sure to make your foam thick enough to keep the wall sheathing above the dew point in winter.

    Lucas's suggestion -- following the REMOTE or PERSIST approach as promoted by the Cold Climate Housing Research Center in Fairbanks -- is an excellent idea.

    Here is a link to the REMOTE manual.

    Here is a link to my article on PERSIST: Getting Insulation Out of Your Walls and Ceilings.

    If any GBA readers are curious about the type of wall assembly that D'Arcy is considering -- the type shown in Figure 8 in the BSC document -- I am reproducing that image below.

  5. GBA Editor
    Martin Holladay | | #5

    I'm not sure what type of problem you are having with the spam filter, but feel free to e-mail me with details of your problem so we can try to help. My e-mail address is martin [at] greenbuildingadvisor [dot] com.

  6. user-2214438 | | #6

    Thank you very much for your advise in this matter. I am pursuing the REMOTE system further, with Ilya of the CCHRC in Alaska. If I can share anything insightful in followup, I will.

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