Basement flooring: Rigid foam as subfloor?
I am about to replace the carpet in our finished basement with something less susceptable to mold & mildew. My plan is to install the following:
- Delta FL as a vapor barrier and air gap (taped at seams).
- 1″ XPS Rigid foam
- 5/8″ tongue & groove OSB subfloor – *my question lies here*
- Laminate or Vinyl floating plank flooring (e.g. Pergo)
My question is this:
Delta FL claims it is acceptable to lay floating plank flooring directly on top of it. This is because the plank floor floats (i.e it need not be secured) and the Delta FL is rigid/stable. If this is true then my question is why can I not apply the same logic to a subfloor comprised of Delta FL and rigid foam (presumably also rigid/stable)? In other words, with floating planks and a rigid foam subfloor do I need that layer of OSB? I’m not keen to place a giant wood sponge so close to our basement floor.
The basement is not prone to flooding but we’ve had moisture on occassion. Having OSB (or even plywood) in a basement just seems like bad practice. There is no need to nail or glue anything so why is the OSB required? If the foam needs added stability then could I Tapcon + washer them into the basement floor? I would think the plank flooring would do a good job of distributing weight so that the XPS avoids any long-term compression. In my mind I’ve convinced myself that avoiding the OSB layer will do more good than harm.
If I must use OSB over foam then my inclination is to revert to Delta FL and floating plank only. Delta FL claims an R3 insulating value. The extra 1″ of XPS would be great to avoid cold feet but I don’t think it would worth it if OSB is required and the basement ever took water. I wouldn’t be able to stop thinking about whether that OSB was rotting beneath my feet.
I’ve tried to get product installationa/certifications from multiple suppliers (rigid foam, Delta FL, and a plank flooring). They’ve all provided the same canned responses that are not at all helpful.
Lastly, I’m less concerned with product warranties or approved installation methods. I just want to know if what I’m thinking will work (warranty or not).
Thank you,
Brian
Replies
How do you intend to fasten down the 5/8 subfloor? It will not lay flat under just it's own weight. OSB or not if the basement ever takes on water the laminate floor is history.
RE: How do you intend to fasten
Mike,
If I use the 5/8 subfloor then I would secure via Tapcons every 2'. My arm will be numb but I've got a hammer drill that will make it easier. I would use the same approach if only using rigid foam (except I would add washers).
Point noted on laminate flooring (although anything is better than our current carpet). While I've not used it previously, I believe the new vinyl plank flooring products do not include a fibrous backing (I believe it is 100% vinyl and hence waterproof). So if the vinyl plank gets wet it will not be destroyed. Also, I would assume that a little fiberboard (just what's in laminate flooring) is better than a lot of fiberboard (OSB + laminate). As I said in my original post, it feels like I'd be installing a big sponge under my floor with questionable utility.
I would like to be convinced that I'm correct (use only Delta FL + rigid foam) but I posted on FHB in the event that I'm wrong. I'm a hardworking homeowner, not a member of any trade.
BTW, we live in Chicago where basements are damp.
Thanks!
Brian
BTW, we live in Chicago where basements are damp.
I don't know enough to respond to the rest of this thread, but I'm in a very old house in VA right now, and the rain comes in sometimes when there is a lot of precipitation.
I have a little clip fan hanging/blowing along one of the exterior walls to generate a circulation.
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I've had that thing running for almost three years now... 24/7. Keeps the air moving in the basement and no mold problems; although I also have a dehumidifier I turn on when the relative humidity gets up in the 70%+ range...
Just an idea for you in case it helps. Of course, the air handler is also in the corner of the basement and the ducts are wicked leaky, so any time the heat or A/C is on there is additional circulation down there. (This is a rental house or I'd do something about the leaky ducts.)
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Squeak, squeak
I'd only be concerned that the unrestrained foam might squeak from rubbing when you walked on the floor.
Deflection
I think you're overestimating the capacity of the laminate flooring to spread the load over the foam. If you have any access to the kind of flooring you have in mind, try interlocking some pieces over a raised square frame with, say, 3' sides. See how much deflection there is when you press down in the center. That deflection is going to be what happens to the foam underneath. Consider the load of one end of a sofa with a 200 lb. person sitting on it. Imagine the wife coming to sit in his lap, then add one of the kids. It happens. Another test would be to get a sheet of the foam and lay some of the planking over it, and jump heavily in the center, and see how it feels. It would be unlikely that you'd have a measurable compression in the foam, but if the flooring feels spongey when you jump on it, I think it's a safe bet that the foam will accumulate lots of broad flat dents over time and end up uneven. Better yet, try it on top of a piece of the FL, and see if you can "read" the pattern of the FL on the underside of the foam. If so, then an installed floor would be subject to little compressions on the underside, too. The plank flooring is not going to conform to the shape of a variably-compressed foam underlayment, and I suspect that you'd end up walking across a floor and feeling the planks dropping 1/32" or 1/16" to the compressed foam here and there, where the greatest compression occurred.
As another poster mentioned, if you get water down there, the plank floor is ruined anyway. If I were you, I'd suck it up and follow the standard instructions, and not get too carried away with making the basement room palatial.
Thanks Bob. I suspect you're right and I really don't want to gamble on this given the time and expense to correct this if I'm wrong. Since FL & plank flooring (no other underlayment) is approved by the manufacturer that is what I've opted to do. We won't have the extra R5 from the rigid foam but it will be simpler and low risk (and less work!). Also, we won't sacrifice 1.5" of floor height.
I used FL only with laminate and it's worked fine except for...
now I have a hole in the laminate where one of my kids dropped a wieght or a pool ball or something and it just popped a hole in the laminate. I think that's the risk with laminate directly over FL. Good thing I have a rug covering the hole....
Frank
Any long term issues with the luxury vinyl flooring over FL?
Your question was the exact same question I have been dealing with. I wanted to use a luxury vinyl plank flooring over DMX 1-step which is a similar product to the Delta FL because I like the idea of a waterproof subfloor and flooring combination. The manufacturer told me the luxury vinyl plank I was looking at was too thin (3 mm) to mount directly onto the 1-Step product, they require an 8 mm minimum floor or a plywood subfloor ontop of the subfloor. Their concern was that the vinyl plank would eventually creep and deform due to the negative voids in the subfloor. Did you have any issue with this? How thick was the lyxury vinyl flooring that you used?
Thanks,
Fix Moisture First
Basements will always have moisture; it's the nature of the beast. Your first priority is to get that moisture out.
Realize that basements are never taken seriously by builders. Little attention is given to details and fnishes. Ventilation is always below par. You need to fix these things first.
Place your face down at floor level and look across the floor.You'll see that the floor is nowhere near as smooth or flat as, say, the driveway.All those little dips trap moisture.
At a minimum, use a concrete saw to cut shallow grooves across the floor, to allow water to drain to the sump. Sumps always seem to be set at the highest point of the basement, anyway.
A better solution is to have a thin -as thin as 1/4"- layer of gypsum cement or other specialty product applied. These products apply quite a bit 'thinner' than ordinary concrete, and self-level much better. You'll have a much flatter, smoother floor, one that drains much better.
Homes are NOT designed to condition basement spaces. The furnace, air conditioning, and ductwork are not adequate to the job. Basement also suffer from a real lack of fresh air. Small wonder basements smell 'musty.'
You control this with humidity-controlled venting. At one end is a vent fan, controlled by the humidity level, that exhausts moist air. At the other end is a vent that lets fresh air in. In-between is a furnace or air conditioner to make things comfy. Naturally, the "gold standard"of basement heating would be in-floor radiant heat :D
"Natural" or passive venting is not enough. Basements never have enough vents.
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Otherwise, a layer of foam suppporting a sub-floor is a good plan. Unless you have radiant heat, the floor will otherwise feel cold. Your feet also want a floor with a little 'give.' Carpet and such is fine, so long as it's kept in pieces small enough for you to carry it out wet. "Wall-to-wall" carpet is a mistake.
Foam will also keep flooring material above most water issues- just be sure that you have addresses the issues I mentioned; make sure water can drain under the foam. I'm just thinking here, but perhaps a "waffled" membrane (like Ditra, or that used outside the basement walls) would work even better as a base than the foam.