I can't quite visualize how the perimeter edges of of a concrete slab ,with ridgid foam insulation installed, are treated for a concrete pour. I'll have 2" ridgid foam layed down on top of a vapor barrier for the "field of my floor, and 2" ridgid surrounding the perimeter. The foundation and the walls are already installed. This is a garage. So when the contractor pours the floor does he come up just to the top of the perimeter insulation, leaving the top exposed or does he cover the top of the ridgid insulation an inch or so? I've heard that in some cases that the top edge of perimeter foam is cut back at a 45 degree angle and the concrete fills that void. Would you need a piece of rebar in that void to prevent cracking? Also, I would very much like to install ridgid foam on the edge of the slab where the cars enter the garage, some say not to do this due to the weight of the vehicles running over that section. If I did the 45 degree cut back with a section of rebar in that void do you think it would hold up and not crack ? Thanks RDB 

fiddlers407,

Are you stating will will have 2" foam over general area but 4" for the perimeter? If so, the top must all be on one plane. Otherwise yes you will create a stress concentraition at the transition. Slabs need to be the same thickness through out the poured area. small diff is ok if gradual.
If you proceed with the extra perimeter foam depth, you'll need to dig 2" of fill out for it. Depending on your fill, this can be a pain.

We had a large walkout basement poured last week. We insulated the front half where the radant heat and living space would be. We planed the foam would be 3/4" above the footer. Latter we placed 3/4" foam over the footer. In the end, we have a 5" thick slab, through out.

Patrick T

I will not be adding any height to edge of the slab, but rather to the width( thickness) of the perimeter ridgid foam(4") for additional R value. Everthing will be on the same plane, but it strikes me that if the pour is brought up to the top edge of the foam I'll have a pink stripe visable around the entire perimeter of the slab. Seems kind of odd. Or is it the case that the pour goes an inch or so over the top of the foam. Thanks RDB

fiddlers407,

 

Now I understand, vertical insulation as in expansion joint area. A 45 deg cut is OK but, you may have cracking. I assume you will have sheet rock and maybe trim? This should cover most of it.

 

Patrick T