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Basement floor assembly

user-5296010 | Posted in General Questions on

I’d like to put in a floor similar to what yacpro13 mentions here:

I’ll put down a layer of 6mm poly, then 1″ of 15psi unfaced EPS. Would this be a suitable tape for taping the EPS seams?:

Also, is there any value in putting a thin bead of canned expanding foam (e.g. Great Stuff) at the bottom of the EPS seams or should I not bother? My only concern there is that the expanding foam might raise the EPS seams off the floor.

For the subfloor layer, I’ve checked around on local lumber stock and pricing; osb t&g is much more abundant and considerably cheaper than plywood t&g. Is there any reason not to use 23/32 t&g osb, anchored with tapcon through the assembly down to the concrete, instead of t&g plywood?

Concerning the climate and basement condition: the home is in the middle of Utah, which is dry most of the time. We’ve been in the house for 3 years and haven’t had any moisture problems in the basement; a couple of stains on the concrete here and there, but I’m guessing those probably happened during construction.

Thanks for reading and for any advice you may want to give.

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  1. andy_ | | #1

    I don't think you'd get much from foaming the seams. Same for the tape IMO. The poly should be a good vapor barrier, so why seal the foam?
    As far as OSB vs Plywood, if moisture truly isn't a concern then there is no reason to not go with the OSB. Both would swell a bit with moisture, but quality plywood shrinks back uniformly while OSB would remain "mushroomed" at the edge or anywhere it got really saturated.
    Having done a couple of these, I've learned to despise tapcons if the concrete is any more than a year old. What I've done that I liked much better from an ease of install standpoint was to put down sleepers with the foam in between and screw down to the sleepers allowing the whole system to just float. Mostly we've used this approach when fitting a sloped garage slab with tapered sleepers so that the final floor would be level.
    I realize that the sleepers are a potential thermal bridge, but on the plus side you're not puncturing your vapor barrier or floor.

  2. Expert Member
    Akos | | #2

    Provided there is no moisture issues, OSB works much better as it is flatter. Tapcons are pretty easy to snap, there are better masonry screws out there, check pro tool supply places. If you don't have a rotary hammer drill, either rent or buy one, WAY quicker.

    Vapor transmission depends on surface area, small holes in the poly from the screws don't change the amount moisture that can move through it, I wouldn't worry about it.

  3. user-5296010 | | #3

    Thanks for the responses.
    @Andy, I'd love to hear more about your experiences with tapcons and why you despise them.

    @Akos Are there any particular brand of masonry screws you would recommend?

    1. Expert Member
      Akos | | #4

      You'll have to check locally. My supply place has Powers Fasteners ones. The local box stores also carry CobraTap ones which work better.

      Make sure to blow out the hole after drilling before the screw goes in.

    2. andy_ | | #5

      As concrete ages it gets harder. Putting tapcons into old concrete tends to snap a lot of them. The philips type heads on them can also strip.

    3. Expert Member
      MALCOLM TAYLOR | | #6

      I don't enjoy using any concrete screws, but these are a lot better than Tapcons:

  4. user-723121 | | #7

    Here is what I have used for decades, you will want a hammer drill. Most big box stores carry these, used to be called Rawl drives.

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