Questions on Insulating Basement Floor

bantoniewiczOctober 22, 2009

We're seeking to finish our basement floor (walls are already done) including insulating it. Based on our research, we've decided to go with an XPS base (1"), plywood sub floor and FLOR carpet tiles (for ease of clean and removal - two young boys).

My question is regarding the installation technique. My plan is to follow the technique as outlined by "mmcarty", "... Use 1" to 2" XPS on the floors. Use tongue and groove or shiplapped sheets and tape all joints. Leave a 1/4" gap at the walls and fill with expanding foam. Cover with 1/2", 5/8", or 2 sheets of 1/2" plywood tap conned through the XPS to the floor..."

So the big question is - Does this mean you do NOT have to install 2x4 sleepers? In other words, can I simply install the plywood (5/8" T&G) on top of the XPS (T&G, caulked and taped) and then anchor it to the foundation with tapcon screws. This appears to be the easiest, most energy efficient and head room efficient of all of the methods. I had always been told that you need to install framing first with a 6mil+ vapor barrier. I don't want to have to re-do the install.


p.s. Our basement is in Chicago, no water to date (3 years, worse flooding in Midwest history). There is some general moisture. Also, we have HVAC with a humidifier and central air and I plan to install an Oregon Scientific indoor thermometer and humidity gauge. As well the walls are brick with spray foam insulation behind and through the framing studs with green board drywall.

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See Building Science Corp. reference below.

No sleepers needed. BSC calls for two layers XPS, first layer attached by concrete screws; glue or screw the second layer to the first. Framing sits on top

Here is a link that might be useful: See RR-0202 Figure 15

    Bookmark   October 22, 2009 at 1:25PM
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Woops! That's two layers of ply ontop of the XPS.

    Bookmark   October 22, 2009 at 5:42PM
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you seam an xps expert. LEts say the above floor is done as described and somehow there is a flood...a washer hose bursts, a water heater lets go etc. Wjat need to be done...must all xps be removed?

    Bookmark   October 25, 2009 at 8:30PM
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