GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter X Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Cold Climate – New Construction

user-1066984 | Posted in Energy Efficiency and Durability on

I’ve been reading in this site for about 3-4 weeks now and it has been a great resource.

Most of the homes discussed are warmer weather climates

I live in Northern Ontario (Canada) and will be building a new house in the spring. My building inspector in my area says it’s a zone 2, but that does not tie into what I have been reading here. I consider it to be cold weather climate as we are about 4 hours drive north of Toronto.

Will be buidling a 3000 sq foot raised ranch on 10 acres in the spring, with 4 ft in the ground (concrete) and a 4 ft knee wall(lumber) on top to give a full 8 foot basement.

I am having a diffcult time with a couple of things:

1. Insulation:
The code here states that we must have a vapour barrier on the inside wall (under drywall).
My question is why do I not see more examples of isoboard insulation on the inside as it could act as a vapour barrier and provide a thermal breal between the drywall and studs?
Also would this eliminate the possibility of OSB rot on the outside under the iso?

2. Footings
I have seen examples of where 2″ xps has been used under the footings and under the slab, basically creating an evelope around the concrete. My architect is suggesting that i only put it under my slab. What it the best method.
I will have radient floor heating from a geothermal system

Attached is a plan for refrence.


Brian K

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. HGWNwRfBXY | | #1

    Hi Brian,

    With regards to ISO board on the inside I suspect there are a few reasons why:

    Its expensive
    Hard to find (at least out west)
    Make construction details more difficult to install (electrical, plumbing, etc.)
    Makes the wood frame wall colder

    Technically I think its possible to do, but not sure its worth it over much easier to install and detail exterior foam board applications.

    Regarding the XPS under the footing there are structural considerations that need to be taken into account. I'd consult and engineer on that. Again it may not be worth it in lieu of ensuring moisture proof details are in place...I can't imagine it would benefit the energy conservation greatly to have it. I do think foam board on the foundation wall below grade is a GREAT idea or at least a water proof liquid applied membrane and a dimpled membrane.



  2. GBA Editor
    Martin Holladay | | #2

    By "isoboard," I assume you mean polyisocyanurate, a type of rigid foam.

    The fact of the matter is that many builders in cold climates have been using rigid foam on the interior of their walls for over 20 years. There are three main disadvantages:

    1. Drywallers and electricians don't like these wall systems, although the perceived disadvantages can be overcome, especially if you choose to strap the wall with horizontal 1x3s or 1x4s.

    2. The interior foam makes the OSB wall sheathing colder (and therefore wetter) rather than warmer (and therefore dryer), raising rather than reducing the risk of sheathing rot.

    3. Interior foam doesn't address the rim joist area. Exterior foam does a good job of insulating rim joists.

    Concerning the use of foam under footings: there is a GBA article to answer your questions. Here it is: Foam Under Footings.

    Finally, there are several details on your proposed house plans that could be improved. To my eye, the most glaring is the lack of ceiling insulation over the exterior wall top plates. I strongly advise you to specify a different type of roof truss. You need raised-heel trusses with deep heels. There are sometimes called "energy trusses." You need a roof truss that allows the installation of full-depth insulation directly over the exterior top plates. You should aim for R-60 ceiling insulation in your climate.

  3. user-723121 | | #3


    In Canada I would build a double wall. Warm side poly, blown insulation, high perm exterior sheathing with housewrap and rainscreen.

    So much good information came out of Canada in the 1980's about superinsulation, revisit this. It was great information then and it is great information today, and it works! There has been little or no improvement on how to build better in a cold climate than the superinsulated house.

  4. Boro | | #4

    Take advantage of the concrete thermal mass!
    I recommend placing the ISO board on the outside of the entire foundation wall. Install a vapor barrier to protect the ISO (I used EPDM pond liner on my house), followed by cement board.
    Anchor to cement with Tapcon screws and flat head timber screws for the wood.
    Parge the cement board with lime plaster. It is more flexible than concrete.
    I did this for my house and the interior walls are dry and warm to the touch.

    Attached is the spec sheet for the insulation under the footings.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |