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Continuous insulation under slab

Adam Smerchanski | Posted in Building Code Questions on

Hi all,
I am looking for some advise on the design of our thickened slab for a “pretty good house” in Kenora, Ontario (climate zone 7).
The house will be 32′ x 24′ with a loft. We are planning for 6″ of rigid foam under the heated slab. Our designer and engineer are adament that the rigid cannot be placed under the footings and under the post. They are telling me this is against the Ontario Building Code and that the engineer will not put his stamp on it.
I am wondering if anyone else has come across this in Ontario?

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  1. GBA Editor
    Martin Holladay | | #1

    I suggest that you contact people at this company:

    Legalett Canada
    103 Warner Drive
    Long Sault, Ontario, Canada K0C 1P0
    Phone: 866-299-7567 or 613-936-0518

    The company sells EPS for use under concrete footings. Oh -- and they are located in Ontario.

  2. GBA Editor
    Martin Holladay | | #2

    The image below came from this Legalett web page:


  3. GBA Editor
    Martin Holladay | | #3

    I don't know about the Ontario Building Code -- but the photo below gives you a good idea of the attitude of Ontario's Ministry of Transportation.


  4. Adam Smerchanski | | #4

    Thanks Martin,
    I'll look into these guys. I've gotta say I was pretty shocked on the response from the designer and engineer but after reading your blog on Friday, I guess it is still unfortunately the status quo. After following this website over the past year and a half, and researching how I wanted to build our house I guess I just took energy efficiency for granted. Why is it that energy efficiency so foreign to people when it just plain makes sense? Thanks again for the response and the great website!

  5. Expert Member
    Malcolm Taylor | | #5

    This may change over time, but presently thickened slabs are still rare in Canada. That isn't to say there aren't a lot of shallow foundations with slabs, but they are usually built as stem walls on footings with a slab isolated from the foundation walls by foam. That solves the problem of having the foam under your load-bearing elements.
    Similarly, interior loads are usually picked up by concrete piers on footings. They do represent a small thermal bridge, but the area is very small.

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