3 season porch over concrete

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Old 09-19-10, 11:01 AM
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Location: US
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3 season porch over concrete

I have a porch on the front of my house and I want to cut it in half to expand on my living room. Right now its carpeted so I pulled up the carpet and plywood under it and there is a concrete pad that has 2x4's over it to raise up the subfloor. Now when I knock out the wall and put a wood floor over this (The plywood is old so I will replace it) do I want to insulate the space between the concrete and my subfloor? I am assuming that it will get a little cold if I don't. Also do I want to put down any kind of vapor barrier between the concrete and the insulation? I know the vapor barrier is supposed to go on the warm side but it seems like it would be more benificial keeping the insulation dry.
 
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Old 09-19-10, 11:20 AM
Join Date: Mar 2005
Location: USA
Posts: 6,126
Since you are in MN, the concrete can certainly get cold because of the exposure under it. The vapor barrier is not just for protecting some inferior types of insulation like fiberglass to keep the moisture from condensation outside of the conditioned space.

I would suggest using extruded polystyrene (EPS) between the that can be a vapor barrier and applying some foam in any voids between the foam and the wood 2x4s. Then follow with the plywood and whatever is required under your flooring.

If you use something like fiberglass, you will still have deal with the moisture that a pieced vapor barrier under it does not handle.

Dick
 
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