Frost Protection for an Existing Foundation

I recently did a remodeling project that involved replacing a three-season sunroom with fully conditioned living space.

My plan called for excavating to the bottom of the existing footing and installing a continuous layer of rigid polystyrene insulation against the foundation wall, all the way down to the base of the footing.

The footing was barely 24 inches below grade.

We did have to do some fiddling to get the foam to lie neatly against the foundation in areas where the concrete was a bit rough, but this was a minor problem.

We also lined the trench with filter fabric and installed a 4-inch drainpipe that ran to daylight, before backfilling with clean 1-inch stone.

The owners have been happy with the result, and so have we: It allowed us to fill what could have been a painful void in our schedule with profitable work.

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