Insulating foundation Wall and Floor

[ckrzysko]

I have radiant floor heat in my attached garage. I used Double bubble on the floor and insulated the wall with 1 inch but didn't go up the foundation wall. So the concrete goes to foundation to foundation.

My question is two parts: I'm building a detached garage and was wondering if anyone ever put down 2 inch 4' x 8' - 250 series Owens foam board under the slab? I already have the 2 inch foam board on the foundation going to sill plate. My concrete guy tells me to leave it and then cut it back to the slab height. He stated, This will stop the floor from wicking to the outside wall. Friends tell me to just put it down on the floor and leave the sides as is. This method the 2 inch foam board is not showing around the perimeter.

Should I have the concrete guy pour the slab with insulated side walls or have the slab poured on top of the foam board (not exposing the foam board)?

Is 2 inch foam board overkill on the floor?

Thanks you for your input!

 

[ForceFed70]

So If I understand correctly, you insulated the inside of the stem wall with 2" foam all the way up the stem wall. But your concrete slab won't be resting on top of the stem wall. When you pour the slab you'll have a 2" ring of foam around your entire slab separating the slab from the stem wall.

I wouldn't do it. I'd remove the insulation at slab height and have the slab poured right up to the stem wall.

1st - Check code in your area. It's common for a requirement to have the slab and stem wall connected via rebar. It's very common to drill holes in the stem walls for the slab rebar to be inserted into. I would think that 2" of foam between the stem wall and the slab would interfere with that.

2nd - I'd be worried about that 2" strip of exposed foam breaking down over time. Bugs, dirt, water, table/chair legs, etc.



Also - With a heated floor you're crazy to insulate the foundation/stem walls and not insulate the slab. Most of the heat loss will be through the slab. So yeah - definitely use the foam under the slab if you're planning to heat the floor.

 

[RayBob58]

I put down that exact foam board, under the slab and on the walls, but not to the top of the slab. Check my build thread for pics. You also need a vapor barrier under the foam. I'm sure I'll wick a little heat out the slab to the walls, but I'm convinced it's minimal. Others tried to convince me that my world would come to an end if I didn't go to the top of the slab with the foam, but so far that hasn't happened.

 

[Radix2]

I ran the foam right to the top of the slab - actually the concrete guys set the foam top with the lazer and used it to set the floor height while placing and screeding. I have 3in up the foundation walls, made up of a 1inch and 2inch layer - the 2inch layer is cut at a 45 so that there is only 1inch at the top of the slab. The 1inch visible will be covered by the thickness of the drywall and the baseboards.

 

[joe--h]

Double bubble? That the bubble wrap with foil on it? Absolutely useless under a slab.

EPS (beadboard) under the slab & cut the foam at an angle to the top edge of the slab.

EPS is cheaper, type II is more than adequate.

Joe H