Turning a previously enclosed porch into a bathroom- how to insulate slab?
I am renovating an old house in Climate Zone 3. A previous owner turned an enclosed porch into a study. It has a concrete slab on grade floor, stone columns, and a low brick wall at its perimeter. The exterior finish is a layer of Celotex (I am assuming this is an insulated board) and stucco and the wall cavity as constructed is about a foot thick. It is sort of framed up as a double wall. There is an almost 5 inch step up into the adjoining room, so I have plenty of space to build that floor up with insulation. I want to finish the floor with tile. I am trying to figure out the best way to air seal and insulate this space. I have read several GBA articles on insulating below grade slabs in basements, but haven’t seen one related to an above grade slab. Would it be treated the same way- maybe 2″ XPS, one or two layers of subfloor, backer board, and tile? Attached is a photo of the gutted space.
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