I'm renovating my whole basement but I'm starting with the "cold" room as I'll be moving some mechanicals in there. The cold room is one of those old storage rooms people used to use as a pantry/larder or as a fridge/freezer in the winter. It sits right under the front porch, measuring 4' x 6' and with a ceiling height of 7' 5". It had a 1' x 1' vent to the outside but I've patched that closed already. The ceiling is a concrete slab (top step of the porch). Walls are concrete block.
My first thought is to glue 2" rigid foam to the ceiling. Then frame the walls with 2x4s leaving about a 1/2 to 1" gap between the frame and the wall. This would mean that the top plate would be in contact with the rigid insulation of the ceiling. Attaching the frame at the top would mean drilling through the insulation before hitting the concrete.
I could instead frame the walls first, attach the top plate to the ceiling directly and then insulate the ceiling with rigid foam.
I'd finish both by using spray foam to insulate the walls and use treated wood for anything that touches concrete. I would also probably use a sill plate in conjunction with the treated wood. Then use strapping on the ceiling to hold up dry wall.
Which would be better? I can see pros and cons to both approaches. Or should I do something different?