Thermal breaks when enclosing porch
I have a stone porch in front of the house (6’x25′) in lower New York (climate zone 4), that is surrounded on three sides by the house and garage (fiberglass batt insulation c.2005 construction). Only the front is exposed and open. The floor is stone, presumably on a concrete slab. The siding is cedar shakes, with a 6″ protruding stone chair-rail around 3′ off the ground in it, and stone facing below that. The roof line continues down over this area (with a nice bead-board ceiling with high-hats in it). I’d like the room to be enegy efficient as I’d like to use the minimum in HVAC for the room.
The lip of stone porch floor sticks out around a foot beyond the natural formation of the new wall filing in the space between the supporting columns, which are also in line with the garage and house. So I think I have to insulate on top of the stone floor: building a new floor up around 4-5″ (there is room), as I couldn’t have a thermal break if I insulated outside the porch (because the door would be set 1′ inside it … thus exposed stone with no thermal break). ALSO, the stone chair rail and stone facade, which comes around the front of the house and garage, and then into this porch area will conduct cold too.
So a couple questions:
1) Is there that much heat transmission through the exposed stone floor that I need to insulate it, and if yes, then I see my only option as a built up insulated floor with 2×4 sleepers, 2″ XPS, plywood, and then tile or something.
2) I assume I’ll remove a 4″ width strip of cedar shakes, and build the new wall flush up against the tyvek underneath it maybe with a strip of silicon caulk between the new 2×4 and the tyvek. But the lower half of the wall has the stone chair rail and stone facing. Should I cut a 4″ channel into those too? Is the thermal bridging that big a deal?
3) and finally for the roof/attic, I was planning on somehow getting a flexible cover up through the high-hat light holes to protect the lighting, and then filling the whole cavity with cellulose. My thoughts are: that’d be easier than spraying foam, as it would distribute itself better … and I want the insulation against the ceiling, rather than the roof, as I wouldn’t want the heat to be above the ceiling.
4) in terms of actually heating it, I was thinking of just an electric heater – maybe blowing from under a bench, but this is south facing, and I’m hoping will have excellent insulation properties (including lots of fixed glass), so hoping for some significant solar gain (maybe even incorporating a Trombe wall?)
Any advice and thoughts greatly appreciated.
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