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Community and Q&A

EPS on basement floor?

gozags | Posted in Green Products and Materials on

Been slowing remodeling our 1930’s basement, in part with help from this site. Thank you.

I have a couple questions about materials. Currently I have 2″ xps foam from floor to ceiling, spray foamed top and bottom and taped. Followed by framing wood framing and Roxul batts (r25 total). The walls are concrete, 9-10″ inches thick. 7-something ceilings (varies) with about 50/50 below grade above grade (brick veneer cape cod style, perched up a bit). The insulation has made an incredible difference so far.

Looking at the floors now. I think we’ll end up doing tile in about 250sq ft of the space. Another 250 will be bare concrete (utility and storage). The remainder is already tile (storage, bathroom, laundry). I have an aprox 11×14 space that will be a spare room and I would like to do carpet, carpet tiles in there. My plan is to put down eps or xps, t&g subfloor (Advantech prob). Head space is a problem, so I was thinking .50 or .75 of rigid foam. I know that’s not much, but I am hoping the thermal break will help. Been getting temps from the concrete floor for about 6 months. Low single digits overnight here and the lowest temp was against the wall at 59 and the average throughout the basement was 62/63. Would thinner foam work in this case? I know the fear is hot air condensing on the concrete.

The only eps I can find is R-Tech, around here. It has a foil on one side and a film (removable) on the other. Would that work? What about removing the white film and putting the foil side up, taping the seems?

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  1. gozags | | #1

    Forgot to add, Spokane WA, zone 5b

  2. GBA Editor
    Martin Holladay | | #2

    Thicker foam is better than thinner foam, but sometimes a low ceiling height requires a compromise like the one you are contemplating. I wouldn't go with less than 3/4 inch of rigid foam.

    The foil facing on the rigid foam won't cause any problems.

  3. charlie_sullivan | | #3

    Taping the seams is a good idea, and either facer will help make the tape stick.
    For a space-limited application, "Neopor" graphite infused EPS gives you a little higher R-value. And unlike XPS, that advantage is stable over time and comes without a major climate impact.

    There's a large EPS manufacturer headquartered in WA that offers Neopor as well as other EPS options.

  4. Dana1 | | #4

    The slab temp will be lower once you insulate it. The deep subsoil temperatures in the Spokane area run about 50F, so with R2-R3 above the slab you'll probably see year round slab temps in the mid- 50s, maybe high 50s

    Fortunately the summertime outdoor dew point averages in Spokane are below 50F, so even with thin foam you won't run into summertime moisture adsorption issues in any wooden subfloors or rugs.

  5. gozags | | #5

    Great. Thanks guys. That was my concern, the dew point. The basement is dry and not particularly humid. Though, older homes around me have rock foundations and those can be a bit musty.

    I'll look for the higher-r, lower eps. All things considered, if I use the r-tech product I'll prob put the foil side up, I am thinking.

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