Stem wall insulation

[Dr. Brown]

Hi guys, I’ve searched but still did not find my answer.

Location: Eastern Canada. Maritimes.

Planning on doing a 2foot stem wall on my footing for my garage. Running radiant floor heat and will have the slab insulated underneath. To insulate my stem wall do I insulate the interior side or exterior? I am unsure if I should have a thermal break between the slab and the stem wall? I have heard of guys cutting the interior rigid foam at a 45degree angle to allow the slab to touch the stem wall.
What have you done?
I am unsure and a novice to this concept.

 

[ConCretin]

I'm not clear on your plan with regard to the 2' stem wall. Presumably your footings extend below the frost line. Do you mean the walls extend 2' above the slab?

In any case, you want vertical rigid insulation on the face of your frost walls to block the cold from freezing the soils under your slab. You also want a thermal break around the perimeter of the slab and insulation on the face of your stem wall above the slab.

I'd form a slab shelf on the inside face of your foundation reducing the wall thickness to 4" (assuming you will have 2x6 wall framing). Run your rigid up the inside face of the frost wall and run your under slab insulation horizontally onto the slab shelf. You can complete the envelope by adding another vertical piece on the face of the stem wall that terminates under the wall plate that's flush with the framing for easy concealment.

You'll have a complete thermal break and envelope without having exposed insulation you'll need to cover or protect.

 

[Dr. Brown]

Thanks for the reply Willysfan. Yes, the idea behind my stem wall is that it will be 2’ above the slab.
I like your point about making a slab shelf. I will mention it to my concrete guy. I was wondering if I ran the rigid up the exterior, how might that affect my heat loss.

 

[Kaizen]

Rigid exposed will eventually deteriorate. The slab should have exterior insulation and I’d go up on the wall as much as will be buried. I’d do inside insulation as well. Depends how they pour if they can make a thermal break. Worry mostly about the slab


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[rburke65]

You could do both .... insulate inside and outside of the stem wall. If only one, then I would do outside.

 

[ConCretin]

As Kaizen correctly states, exposed insulation will eventually deteriorate especially in sunlight. This is why I'd always run it on the inside. A slab shelf/stem wall detail allows the insulation to extend all the way up to - and flush - with the plate for easy concealment if you install drywall, etc.

It also provides for a complete insulation envelope i.e the rigid insulation extends up to wall framing/insulation. This can't be achieved with the insulation on the outside without exposing it to sunlight or having to plaster it, which raises a whole new set of costs and issues.