Floor underlayment or not
I’m getting ready to install 32 sq. ft. of Southern Yellow Pine 1×8 T and G in a small addition on my house. The subfloor is Advantech over PT joists. I had originally built a small foundation and installed the sill and joists. Then I became concerned about moisture from underneath. The “crawl space” was impossible to create access to and would have been too small to service anyway. I should have poured a slab from the beginning.
I ended up filling in the area with concrete and then topping that with a layer of 2 inch foam. I then re-installed the joists and layered foam (cut and cobble style) between the joists.
It is now basically a concrete and foam block. I did line the inside perimeter of the original foundation with foam prior to pouring the filler concrete by the way.
Anyway, I plan on installing the flooring (which will be primed on all sides, painted and face nailed) next week. The finished floor height is slightly lower than the floor in the main house so I’ve got a little room to play around with thicknesses. I was thinking about packing up the subfloor with 1/4 inch strips installed every 8 inches or so to create a gap for drying purposes. The subfloor has been in there for over a year and I haven’t noticed any warping or anything.
Are the strips a bad idea? Should I use a vapor barrier or some sort of underlayment?
Should I do both the strips and an underlayment…..one or the other…..or neither? Neither would obviously be wood floor nailed directly to Advantech.
Any guidance would be appreciated. Thanks in advance.
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Re-upping this to see if I can get a reply.
If your whole floor is floating on foam already, there is no chance of moisture making it in there from the soil. I think you are good.
The one issue I have T&G pine flooring is getting it to not squeak when directly over joists. I've never tried it over OSB though. I would definitely include an underlayment, flooring felt would be my go to.
Thanks for that. I guess I would want the floor assembly to be able to dry in one direction anyway in case moisture did get in somehow. In this circumstance, as long as I don't include a vapor/moisture barrier, I'd be allowing it to dry towards the inside. Am I thinking about this the right way?
Felt sounds like a good idea. I was thinking about going with double layer rosin paper before I started wondering about whether or not I needed a moisture barrier, but maybe felt is better.
Rosin paper works just as well. You just need something under the pipe to let it move a bit.
Thanks Akos.