# Frost Protection on Monolithic Slab?



## trickyjrp112 (Aug 17, 2010)

Hey everyone this is my first time using this forum and I'm hoping to get some help from someone who's worked with frost protection on monolithic slabs in south eastern Massachusetts area or anywhere with a similar issue. The Massachusetts code tells us in order to protect against frost the foundation must extend 48" below grade or otherwise must be protected from frost another way, which I'm guessing 2" ridged insulation should suffice. Attached is a photo of the depth of the monolithic slab.








As you can see the slab will be at a depth of 1'-6" below grade and a vertical ridge board insulation will follow it. Basically my question is how far horizontally (in length) should I go with a 2" ridge board around the perimeter to protect the slab from frost on a residential home??? Or does anyone know of a better solution in order to avoid digging deeper into the soil?


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## mics_54 (Oct 28, 2008)

I normally install 2" two feet deep vertically and 2' out horizontally except at corners where I go 4 ' horizontally for the first 8 feet of wall. Big openings like garage doors get 4" thick 4' wide at 2' depth


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## trickyjrp112 (Aug 17, 2010)

Thanks for the reply mics. I ended up designing the horizontal foam board (R-10) extending 2'-6". Which leaves me with a total of 4' of foam board per foot. The local building inspector didn't seem to care much about frost protection just as long as I met the energy efficiency demands (Rescheck) in my area. Therefore I included it and the home passed. Now just waiting for my client to submit it to see if there's any issues.


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## jhammer7 (Nov 19, 2009)

I did one of these two years ago but we put six inches foam under the slab and four inches around the perimeter. We built the first floor walls at the edge of the slab no crawl space. According to the owners its a nearly passive usage home.

Feel free to message if you have questions.

J


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