Radiant Heat Insulation - Perimeter

[Rye Guy]

I have built a 36 x 26 garage, installed the pex piping, 2" insulation under the pad and on the outside of the thickened edge. (The outside of the thickened edge). I was told that I should use 4' x 8' sheets of 2" styrofoam around the perimeter of the pad to prevent frost from getting underneath the pad. Basically dig down around the pad and then slope the styrofoam downwards away from the pad and then cover with fill. Is this really necessary or was I given some bad advice?? I live in Winnipeg, MB, Canada and the temperatures here can be below -40 in the winter. Any advice would be helpful.

 

[yotehuntersd]

I am building my garage as we speak and I am doing exactly that but I am cutting the 4x8 length wise the height of the slab minus the 2" and then sliding the 3x8 under the piece that is glued to the edge of the foundation and back filling on both. I had steel trim pieces bent that cover the top of the foam and drop down to just below the fill line.

 

[Rye Guy]

Okay. So there is the 2 inch space on the bottom of the slab (in the insulation)?? Then you are placing the 2 x 8 sheet at the bottom of the slab??

 

[jklingel]

In cold places, it is often recommended to insulate down the foundation wall about 4', then go horizontally 2' to 4' from the footer out. I have seen isotherms of foundations w/ and w/out the foam, and it makes a lot of difference. In my mind, you used too little XPS to start with. 4" is a minimum, everywhere, IMO. PassivHaus homes use 14 or 16" of EPS under their slabs. Whether or not that ever gets paid for by fuel savings, I don't know. Glad to see you insulated the slab edge!

 

[yotehuntersd]

I will take some pics soon as i am just about to that part