3/4″ of XPS on a basement floor vs. 1½” in a Climate Zone 7 basement
A friend is planning a basement reno..
it has no insulation at all on the interior or exterior or under the slab. It was built in about 1995. The basement has about 18″ above grade, the balance is underground. It has never had bulk water seep in and its unlikely that there is poly under the concrete as this wasn’t commonplace here (Winnipeg Manitoba Canada).
He wants to add 3/4″ XPS to the floor (1150 sq/ft) and cover that with either 5/8″ or 3/4″ t&G OSB or plywood using only the T&G joints to hold the sub floor together as a unified surface.
I have questioned this and suggested the 1 1/2″ foam under 3/4″ ply with sleeps as suggested in the Strategies and Details section.
Additionally he plans (like most of the unwashed here in the north) a 2×4 frame wall with R12 fiberglass bat insulation for the interior walls: with 6 mil poly to 4 ft below grade (nearly to the floor).
Can someone please help me with some facts why the thinner foam and lack of sleepers is not a good idea and whether his plan for the basement walls makes sense (I would omit the poly all together).
I will get him to tape a square of poly to the floor to see if there is vapour moving through from the subsoil..
Thanks in advance
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