thermal break using expansions board

singh

We can't place insulation on the outside. Because of the architecture. And concrete sub say 2" insulation on the inside mitered on a 45* would crack.

singh

My concrete guy wants to use 1/2" thick x 4" height fiber boards, commonly used as an expansion control in concrete, along the perimeter of the slab.

Is this ok for slab with radiant, is the r-value of this enough?

Couderay

edge insulation

Personally I would use 2" high density foam board (pink stuff)on the outside edges and go below the pad to the insulation you are placing below the slab. Yes more money now, but peace of mind knowing you done it right.

Couderay

Mitered?

You could make a lap joint. Verticle placement of foam board to go past board on bottom of slab. I wish I had a pic to show.The foam board under the slab would end at the edge of the concrete. The edge of the verticle foam would go from the top of the slab to the underside edge of the foam that is below grade a lap joint not mitered.(A "L" shape) As far as cracking what are the concerns of the concrete guy.

kevin coppinger_4

can you.....

compromise? do 1 1/2" or 1 "...edge loss is huge in radiant slab....I would get the architect to sign off on heatloss issues if it comes back to bite you...CYA. kpc

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hot_rod

That's a common dilemma

how to detail the top of edge insulation. Nobody wants to see the raw foam edge inside the building, and it doesn't hold up well. The 45 bevel hides it but a thin edge of concrete is certain to crack, the concrete guy is right in that concern.

I have used this plastic H channel over 1/2" foam. not a great r-value, but better than nothing.

After the slab is poured pull the top strip and use a butyl caulk to fill in.

Now you have a flexible, better looking seal between the wall and slab. Sealed for water and vapor, also.

It's a common problem where driveways ansd sidewalks touch a radiant slab, also. This H cap works great at garage door to slab connections.

hot rod

singh

Thanks for the replies everyone.

No one responded about using the fiber boards, they are also 1/2", but I don't know if the have the same R-value. Are they not a good idea, better than nothing.

jp_2

where exact?

since you say perimeter are you talking all the way around?

is this a garage or basement?

i think the fiberboard would be pretty good for conduction heat, especially if wet.