Sunporch vapor barrier
My home includes a sunporch approximately 8 feet x 17 feet, built on a concrete slab about two feet above grade and 9 inches below the kitchen from which access to the sunporch is made. The two exterior walls consist of 18 inch high knee walls of 2 x 4 construction, insulated, with large windows all around. Space is unheated.
My plan is to raise the floor to the same level as the kitchen so access is easier as we get older. Will use 2×6 on 12 inch centers or 2×8 in 16 inch centers, depending what will fit. Ceiling height is no issue. Finished floor will be engineered hardwood. I will install insulation between the joists.
Where should I install vapor barrier? Directly on the slab, under the joists or under the finished floor? Or, should I install a couple of registers in the floor to let it breathe?
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Hi Sroyce9.
Do you happen to know if there is a vapor barrier beneath the slab? If there is, you do not need an additional vapor barrier above the slab. If you do not have a vapor barrier below the slab or are unsure, or know that the slab has moisture issues, install the vapor barrier (poly sheeting, I assume) directly above the slab.
Also, you could consider laying down rigid foam insulation on the slab (over the vapor barrier) and installing your floor joists (sleepers, in this case) on top of the rigid foam. You may need to rip the sleepers to a specific width to get the sun porch floor in plane with the kitchen floor, but you will end up with a continuous thermal barrier and a nice stiff floor.
Thanks for your advice. Original construction was slab over a foundation separate from but connected to the home basement (if that makes sense). It was a covered porch with roof, no enclosure other than that. Doubt that any vapor barrier exists at the slab. I added the knee walls and windows a few years ago.
> Space is unheated....I will install insulation between the joists.
What is your intended purpose for this insulation?
Do not put concentrated loads on foam.
S. Royce,
It would be helpful to know your geographic location or climate zone.