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Connecting Two Foundations.

In the last post I pointed out that we are doing the foundation pour in two parts in order to allow for  foam to be inserted between the two foundations.   According to my highly simplified calculations,  leaving the porch and house connected lead to a thermal bridge that can leak energy at a rate that is at least an order of magnitude bigger than using the foam and rebar.   The connection is still not 100% thermal bridge free but provides a decent option for connecting the two foundations and will also decrease the flow of energy between the two.  Inserting the foam did complicate things a little but John and the guys from Matchless Foundations didn't seem to care a whole lot about it.  They agreed that the two pours was the simplest way to do it.

Attaching the foam was relatively easy and took about an hour of work.  The procedure was as follows

1.  Cut foam to width of 8" to fit inside the wall form.
2.  Drill holes in the foam at a semi-regular spacing
3.  Snap a vertical chalk line on the exterior of the house foundation that represents the outside edge of the foam.
4.  Place the foam on the foundation and use a drill bit to mark the positions that need to be drilled.
5.  Drill, Drill, Drill....and Drill some 11 more times!
6.  Blow out the holes so the epoxy will adhere to the inside.
7.  Test rebar for fit.
8.  Fill holes about 3/4 full of epoxy.
9.  Insert Rebar slowly, squeezing epoxy out of the hole.  Scrape off the excess.
10.  Apply a good amount of foam compatible glue to the back of the foam.
11.  Fit rebar through he holes in the foam and push the foam tight agains the foundation while squeezing out the glue.
12.  Complete the same procedure for the other foundation connection.
13.  Continue forming the garage/porch foundation.


Will it be worth it?  Without modelling its hard to tell but given that it was such a low cost ($70 + 1 hour labour) it made sense to do it.


  1. Hi David,
    I am finding your blog very helpful as we build our "pretty good house" in New Hampshire.
    I am also planning to use a bond break for thermal reasons between the house and garage foundations. I am interested in finding out if there is some structural engineering analysis behind the approach you show. For instance, why 5 pieces of rebar, not 4 or 6?
    Thank you.

    1. hi Mike, sorry for the late response.. This was a recommendation from an engineer!


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