LVP flooring destroyed my subfloor

[Val Picanco]

Facts I'd like to get out of the way:

We live just outside of Little Rock, AR for climate purposes.
1680sf house with crawl space, vents and vapor barrier on the ground underneath.
About 350sf was an add on over a concrete carport with no vapor barrier, probably not any under the concrete.
No insulation between floor joists

Ok, so we've lived in the house just over 18 years and at least 15 of those were with parquet flooring on plywood subfloor, no insulation between floor joists. At the end of 2016, we started installing the floating, waterproof luxury vinyl planks over a really thick, cushy vapor barrier installed directly over the parquet where we had it, directly over the plywood subfloor where we had carpet. We left the tile in the bathroom alone. We left the parquet in the two spare bedrooms alone.

About the end of summer last year, the parquet started buckling in the middle of the house. I took the vinyl flooring up to see what was going on. The parquet glue was very damp and if I laid a piece that had come loose on something, it would re-stick. It had swelled due to moisture absorption, I assume, and so I went ahead and took a skil-saw and cut a blade width grove every foot, each way and screwed the parquet back down before putting the LVT back down, minus the cushy vapor barrier because the new salesman where we got the material informed us we never should have put the vapor barrier down on top of the parquet on a crawl space.

It was at this point we stopped installing the LVT in the remaining two bedrooms. We had just installed it in the master bedroom where we tore out the carpet when this happened. So, a couple of weeks ago, the individual plies in the plywood subfloor in the bedroom started separating and pushing the LVT up and providing the feel of walking on a cloud. Kinda cool. Kinda #@^%! Pulled a bit of the LVT back and the plywood is damp to the touch.

So, now I'm ready to go, room by room, tearing up the entire floor back down to the floor joists and start completely over. I'm thinking the humidity is being absorbed into the subfloor and getting trapped by the vapor barrier and/or snap locked, waterproof LVT.

My first thought was to attach a vapor barrier to the bottom of the, thankfully, treated floor joists with treated plywood strips that I would screw into the bottom of the joists to keep them from falling. I would then go ahead and drop some insulation into the space to maybe help control air/moisture transfer...maybe. I then saw that faced insulation should always have the vapor face up against the bottom of the subfloor or you can have problems with mold growth in the insulation itself if it is trapped between the conditioned space above and the moisture barrier facing down.

So, now I'm leaning toward just installing faced insulation, vapor barrier up against the subfloor and maybe...?...installing a solid sheet (visqueen) vapor barrier between the top of the floor joists and under the subfloor before we re-install the LVT, minus the cushy vapor barrier. I'm really at a loss at what to do so that I don't have to do this all over again. As I said before, we never had any problems whatsover until we installed the new LVT and vapor barrier.

I would love any feedback on this. I can't help but feel we should have not installed this type of flooring on a crawlspace and were pretty much taken for however much money the flooring company could get us to spend, but that feeling is coming from a dark place in my soul born from a lot of frustration as we now have four different areas of the flooring turning into bouncy castle like surfaces.

Oh, and there is no sign of any problem with the two bedrooms that still have parquet flooring in them. It is all still stuck very well to the subfloor with no indication that it will be coming up on its own anytime soon.

 

[Dana]

The problem is largely the vapor barrier and the vented crawlspace. In the summer the crawlspace allows copious amounts of moist outdoor air into the crawlspace. When running the air conditioning the floor is much cooler than the dew point of the outdoor air in summer, and moisture accumulates in the wood & adhesive as adsorbed water.

With semi-vapor permeable wood flooring & subfloor it could dry into the much drier air of the air-conditioned interior. But with vinyl flooring and vapor barrier on top of the wood there is zero drying- any moisture that accumulates has to dry back toward the crawlspace.

The problem is likely to be more apparent in sections of floor that run cooler due to being in the direct flow of the air conditioning, but there are other factors that may cause it to show up elsewhere too. It's a problem over the entire floor, even if it exhibits itself more in some locations than others.

Insulating between the floor space will not solve the problem. If that insulation super air & vapor tight it creates a moisture trap between the vinyl flooring and the vapor-barrier facers. Using asphalted kraft facers would have variable vapor permeance and might help a little if perfectly air tight, but they can't be made truly air tight, and it doesn't really fix it. IRC 2018 code minimum R-value if insulating between the floor joists would be R19, but that would just make the subfloor even colder.

Installing a vapor barrier under the bottom of the joists doesn't solve the problem either, and it creates a moisture trap. The subfloor has to be able to dry either upward (which it can't through vinyl flooring) or toward the bottom, or both.

The better solution is to air-seal the ground vapor retarder to the foundation walls with duct mastic, then air-seal & insulate the foundation walls, sealing up the vents. This puts the crawlspace inside the thermal and pressure boundary of the house, and with even an extremely modest amount of ventilation of the crawl space with conditioned space air, the humidity in the crawl space will track the moisture levels of the rooms above, keeping the moisture content of the subfloor & parquet flooring well bounded.

IRC 2018 code minimum for foundation insulation is R5 continuous insulation for the US zone 3A counties (most of the state) R10 continuous insulation for the 4A counties (the NW corner counties.) You can use either an inch or two closed cell spray foam, which is inherently air sealing, or 1-1.5" of foil faced polyisocyanurate, sealing the seams with a high quality foil tape. Rigid foam can be tacked in place with blobs of foam board construction adhesive, then securely strapped to the foundation with 1x4s through-screwed to the foundation with masonry screws. In termite-prone areas it's useful to cut a 2" wide inspection strip that can be pulled out and friction-fitted back in place. If cut cleanly with a straight edge and a steel wallboard taping knife that has been sharpened along the edges the friction fit will be air tight enough that it need not be taped at those seams.

With spray foam the foam would often need to be painted with intumescent paint to meet local fire codes. With rigid polyiso there are fire-rated grades that don't need any thermal barriers against ignition (eg Dow Thermax), but even generic foil face polyiso is relatively "safe" compared to polystyrene (EPS or XPS) , faced or unfaced. The gold-standard would be a timed fire rated thermal barrier, which could be half-inch wallboard nailed to your 1x4 furring, which would meet code everywhere in the US.

The band joists can be insulated with just R15 rock wool trimmed cleanly with a batt knife or bread knife for a friction fit, but caulk the seam to the foundation sill and subfloor with polyurethane caulk first, to ensure air tightness to the outdoors.

 

[Sponsor]

 

[Dana]

More Astroturf flooring, mayhaps?