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ST180 12-18-2012 04:39 PM

WV Basement Insulation
I have read through tons of these threads and have learned a lot. Thank you!

I'm finishing my basement in a 1 year old house in WV. Cement block walls and concrete slab. There is no water evident. I do have issues with condensation during humid summer weather and will be installing a whole house dehumidifier. Based on info here, I'm gluing 1" xps on the walls & foam sealing and taping seams. Rim joists will get the same treatment. Roxul will go in the walls. I had planned to do Dricore with a below grade laminate on top, but info here has me rethinking the dricore in favor of 1" foam on the floor with 1/2" plywood on top, still with below grade laminate.
My questions:
Do I need to glue the foam down?
Do I need to secure the plywood down and if so with what and what spacing?
Will the foam/plywood combo be stable enough for a pool table?
Should I build the walls on top of the foam/plywood, or put them on the concrete with the foam/ply butted up to the frame?


Windows on Wash 12-18-2012 06:20 PM

The compressive strength of the XPS is very high and it can be used under slabs in many cases.

I would check with the specific manufacturer and they will have guidelines and provisions to follow.

ST180 12-18-2012 08:32 PM

Thanks for the response. I may not have been clear, though. I'm looking to put the 1" xps on top of the slab with the 1/2" plywood on top of that, as I've seen recommended in many threads here. What I haven't seen is how to fasten this subfloor down and I was hoping to get guidance on that as well as whether to build the frame walls on top of the subfloor or butt the subfloor to the bottom plate of the frame.

Windows on Wash 12-18-2012 09:09 PM

I understood you.

Masonry screws will work but don't go through the entire thickness of the slab.

joecaption 12-18-2012 11:45 PM

I've done it in a slab rental I own.
I used 6 mil. plastic then 3/4 foam with 3/4 Advantec T & G subflooring.
I used 3" long Tap Con screws.
The floor does not move at all and is much warmer.
1/2 sounds to thin to me and would not suggest it over foam.

ST180 12-19-2012 03:05 PM

One other question. There is about a ten foot length of ductwork that runs along the top of one of the outside walls, about 1/2" to 3/4" away from the wall. I plan to frame a bulkhead around the ductwork and the wiring and pipes that run along the ceiling in front of it. I can't move the ductwork. Do I need to worry about getting the XPS on the cement block wall behind the ductwork, or can I leave that section uncovered? If I get thinner XPS will that be ok, and can it be touching the ductwork?

ST180 12-21-2012 06:24 AM

Does anyone know if it's ok to have XPS touching a heat duct? It will be on the wall inside a bulkhead, with 1/2" drywall on the outside of the bulkhead, so is that ok for having the XPS covered?

jackpine 12-21-2012 07:05 AM


Originally Posted by ST180 (Post 1077231)
Does anyone know if it's ok to have XPS touching a heat duct? It will be on the wall inside a bulkhead, with 1/2" drywall on the outside of the bulkhead, so is that ok for having the XPS covered?

I am not sure, but if you go to the manufacturer web site you will get an answer. I am curious though why? Are you trying to quiet down the heat system?

ST180 12-21-2012 07:51 AM

No. I'm putting up 1" thick XPS on all the basement walls prior to framing and there is one section about 10 feet long where the ductwork is hung very close to the wall. I'd like to try and get a thinner piece on that section of wall behind the duct so that I have complete coverage to eliminate condensation. Since I read that XPS needs to be covered by drywall to avoid potential exposure to ignition sources, I'm concerned about the proximity of the XPS to a heat source like the ductwork, especially if it is in contact with the duct.
It's the Pactiv foam board sold at Lowe's. I've been all over their website but they don't address this issue. I haven't called them yet.

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