Winter protection

I am hoping to get the ground sub-floor in place over the next couple of weeks to form a temporary roof over the basement. However, the inside footings need to be protected from the cold to avoid frost damage. The outside of the footings is buried under a minimum of 4 feet of earth (i.e. below the frost line). We placed some old foam insulation (courtesy of Tom) on top of the footings to insulate them from the worst of the cold, and then weighted them down with rocks. Any snow that lands on them won't really matter and will actually help to insulate them further.