Cold climate frost-protected shallow foundation
Im in Climate Zone 6 (60″ Frost Depth) and am building an unheated garage myself. I’d like to use a Frost Protected Slab approach to save on money and for the experience.
I have a good understanding of this foundation style for heated, high-performance homes. But a garage version has me curious over a couple of details. I read this great JLC article from Andy Engel but still have some questions: https://www.jlconline.com/how-to/insulation/frost-protected-shallow-garage-slab_o
1.) I realize I will need ‘skirt’/ horizontal insulation extending out 5’. But do I need vertical insulation around the thickened slab edges? It seems as though it would be destroyed on the front of the garage as cars would be driving over it. Also, it seems pointless given that the slab will always be cold anyways?
2.) Is 2.5″ of Type IX EPS under ‘footings’ and 2.5″ of Type II EPS under the non-load bearing areas sufficient thickness for preventing freezing temps under the slab in my climate? I chose 2.5″ because I can cut it easily with my circular saw… I’ll also have a bed of 3/4″ washed stone under the sub-slab insulation and drains to daylight.
3.) Should I add a drain or slope slab to garage door? Would a drain invite freezing temps below the slab? If I slope, should I use steel shims under walls?
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