Andy Engel

Three years ago, I built a detached garage with an apartment above. Of course, “garage” is a euphemism for “shop.” With a limited budget, I wasn’t planning to hire other contractors and I wanted ways to save both labor and money, starting with the foundation. Living in Connecticut, I’ve long been jealous of builders in the South, where the shallow frostline allows for building on slabs with thickened edges. Here, I was looking at excavating the perimeter down to at least 42 inches below grade, pouring a footing, laying a concrete block wall to above grade, then evenly compacting the backfill before even thinking about the slab. That’s a lot of work and material, and a lot of excavation spoils to dispose of. There had to be a better way.

Section R403.3 of the 2009 IRC provides details for a “frost-protected shallow footing.” Instead of digging down below the frostline, you insulate below the edge of the slab and out from the building a certain distance with rigid foam. The distance depends on your climate. The foam captures the interior heat from the building and the earth’s...

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