New raised subfloor over slab


Old 02-16-08, 11:54 AM
Thread Starter
Join Date: Feb 2008
Posts: 4
New raised subfloor over slab

We purchased an old WPA-built schoolhouse. The building sits on a heavy concrete slab. There has never been interior plumbing in the building. The exterior walls are 18" stone. The interior ceiling height is 12 ft. We want to raise the floor to accommodate plumbing rather than try to cut through concrete or damage the stone walls. We live in an area where termites thrive and have done damage to existing non-bearing studs in the building. This brings the question of how to isolate flooring joists placed directly on the slab as well as the other issues regarding feasibility of our plan.

On the face of it raising the floor seems like a workable plan. What issues might we encounter if we go ahead with this approach?
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Old 02-17-08, 04:19 AM
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Join Date: Mar 2007
Location: Frankfort
Posts: 210
Raising the floor is a great idea. Keep in mind to put down plastic over the concrete first. Concrete draws moisture which can get into the woodwork. Termites love moist wood!
Any wood that even comes close to ground contact needs to be treated lumber.

The new spray on foam insulation is ideal for this type of construction. The foam is highly insulating, will not draw moisture and termites hate it!

Other insulation, such as fiberglass, can be used as well but will be less efficient.

Good luck,

Old 02-18-08, 10:24 AM
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Join Date: Feb 2008
Posts: 4
Thanks for the reply. I wanted to get a sense of whether or not we were looking at this in a sensible way. Sometimes lay-people can do some wacky things. I don't want our place to be one of those "should have done it this way" errors. It is a bit scary going into it on our own.


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