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How can a slab edge be tied into a foundation stem wall and insulated at the same time?

BrucePPH | Posted in Green Building Techniques on

I’m working with the local code officials to find a way to insulate a slab to a footer or stem wall. They are concerned about termite infiltration and structural issues when tying the insulated slab into the footer with rebar. One jurisdiction is allowing R-5 placed horizontally but nothing on the slab edge. I told them the requirement does little for stopping heatloss through the edge. Attached is a design they came up with but the local HBA rep. on the board expressed the concerns listed above.

Connecting the slab through foam products with rebar poses its own set of problems.

Keeping termites out of the home is another.

Is there a solution to this dilemma?

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  1. user-577475 | | #1

    I'm not an expert on keeping termites out but generally I advise against tieing a slab to a foundation with rebar unless other issues require it. Differential settlement and slab shrinkage could cause moderate to severe cracking. However, if this the detail of choice where you build, you can get fiberglass reinforcing which has a lower thermal transfer than steel.

  2. davidmeiland | | #2

    We are required to provide a thermal break between a slab and footing/stemwall. If it's a mono-pour, the exterior of the concrete has to be insulated. I don't see the need for the rebar tying the slab to the foundation, and I wouldn't place the slab on top of the wall either. With proper prep it can float entirely, insulated underneath and at the edges.

  3. BrucePPH | | #3

    Corian/David Thank you for your replies. I'm not up on the IRC but does code require this or is this just a past practice that is no longer relevant? This area has expansive clay soils so does tying the slab to the foundation require the rebar?

  4. E47mJdAip6 | | #4

    You can use an ICF system, and bring down the interior EPS panel to allow concrete to pour from slab into forms. Use termite rated peel-and-stick (Soprema Colphene ICF is one example). R-11 on the slab edge.

  5. BrucePPH | | #5

    Thanks Brad for the product reference. I agree that ICFs would be a good solution but in this environment cost dominates all discussions. The question is how can the builder meet the requirement (code or green) at the lowest cost. The code officials are caught in the middle trying to enforce codes while moving to green without putting builders out of business.

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