Another foam over concrete slab floor question

Discussion in 'Remodel Forum & Blog' started by Chris1973, May 2, 2019.

  1. Chris1973

    Chris1973 New Member

    May 2, 2019
    Hi Dana: I've read the forum and you've given tons of great advice, thank you.
    My main floor in NY is a on-grade cold slab. There is no water-table or vapor problem. I just want to take the chill off the 900 sq foot slab floor. Ceiling height is my problem. My ceiling is 8 ft. Can I have your advice on these choices:

    1) 6 mil poly sheet-> 0.5 inch Foamular 150 4x8 sheet -> 0.5 inch osb -> Laminate underlayment -> Vinyl flooring. (Should I be worried about the foam squeaking on each other when walking on this)?

    2) I'm thinking instead of using: 1.0 inch Zip System Insulated R Sheathing... It's R-3 foam pre-attached to OSB. It's really made for wall sheathing but I'm thinking it could be an easier install, less material to ship/install. I need to check if it's cost effective. I'll still use the 6mil poly and will tape the seams.

    3) DriCore SubFloor R+. 1.0 inch DriCore with insulation attached, 2x2 panels over 6mil poly sheet.

    Dana, are any of the above better than the rest for my situation? Should I decide just using costs of each?

    Can I use floating tongue & groove osb to avoid tapcon screws into the slab?

    Thank you in advance...
  2. Jotun

    Jotun New Member

    Jan 8, 2020
    Hampstead, MD
    I'm looking to do something similar with .5" EPS... could you give us an update with what you went with and how it turned out?
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  4. Dana

    Dana In the trades

    Jan 14, 2009
    Friends don't let their friends use XPS (eg Foamular 150). The reasons are twofold:

    *XPS is blown with an HFC soup blowing agent which gives it it's higher initial performance, but as the HFCs diffuse out over decades it's performance drops to that of EPS of similar density (in the Foamular 150 case, R4.2/inch). While it's "warranteed for life" to 90% of the labeled R, they're counting on never having to pay off on that, since it'll take 30-40 years.

    ** Those HFC blowing agents are EXTREMELY powerful greenhouse gases compared to the low impact isopentane used for blowing EPS. The differences in lifecycle CO2e footprint isn't subtle- XPS is by far the least "green" insulation material in common use today:


    Don't do it. The insulation in ZIP-R is polyisocyanurate (also blown with low-impact hydrocarbons, like EPS) , which is hygroscopic, and will potentially wick moisture up from the slab, or from any minor flooding/leaking/beer-spills, etc. It's fine to use polyiso on the interior side of foundation walls, but not on slabs under subflooring.

    DriCore is also insulated with XPS ('nuff sed), and they're taking credit for the R-value of the other laminated materials in the product to come up with R3.

    I'd recommend going with a variation on your option #1 using 3/4" EPS (any density) for a true R3, now R3 fifty years from now, and putting the 6 mil poly vapo barrier between the EPS and subfloor as a slip surface. Tape the seams of the EPS with housewrap, lap the seams of the OSB by at foot from the seams of the EPS to avoid compression/rockering at the edges.

    With a single layer of OSB you can't really float the subfloor. The sheets of OSB will develop "potato chipping" curl & waves if not secured to the slab. It takes double layer of half-inch OSB glued and nailed to each other with the seams lapped by a foot or more to not run into those issue..
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