Underlayment under LVP flooring
I called Cali vinyl before I did my floor and they said they require underlayment with vapor barrier under their floor for warranty
i told them I had a vented crawl space and asked if that was ok and they said yes many houses with crawl spaces have used our floors with underlayment
so I installed the floor myself with 3 mm foam underlayment over 2 months, started putting up the trim, have toilets and everything else installed
now I’m reading online some people saying to not use underlayment if you have crawl space after Cali vinyl just told me 4 months ago that it’s fine and is needed for warranty, so is my subfloor going to rot now or is Cali vinyl right
i guess worst case I can go under my crawl space once a year and see if the sub floor is damp and if it isn’t then I’m fine?
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Bumping for a new day
If your crawlspace is so damp that there is a risk of moisture rotting your floor, that's a problem that needs to be addressed. Placing a vapor retarder under flooring is pretty common and definitely good practice if there is risk of elevated moisture. Can you describe your crawlspace and why you're concerned about moisture?
I have 6 mil plastic down in my crawl space I’ve put a few holes in it here and there from working down there with tools and stuff other than that not really concerned about crawl space itself, I don’t see any mold and sub floor feels dry to the touch to me
I haven’t seen many people say this but I have seen some, and they said LVP itself is a vapor barrier and it will trap any moisture at all that comes from my crawl space vents or my crawl space floor and will never dry out, even if I have plastic down I will get moisture from outside though my vents
I thought my venting is what would keep my subfloor dry even with a vapor barrier on top of my sub floor inside the house?
The vapor-retarding ability of poly on the ground correlates with the percentage of the poly that remains intact, so a few small holes don't really matter. Crawlspaces that have only code-compliant venting are definitely prone to increased moisture levels, and I won't use them. I either ventilate the space as closely as possible to being completely open to the outdoors, or I enclose, insulate and condition it like a good basement.
LVP is a vapor barrier so adding another layer won't change things.
I don’t need to worry about the LVP rotting my floor then your saying,
If it’s possible for the crawl space to be an issue it seems like the 1st floor bathroom would be more of an issue since there’s some LVP upstairs above it, seems like the moisture from the bathroom would get trapped on the 2nd story floor between the drywall ceiling and LVP floor esp when people take those really steamy showers
I think my crawl space venting is slightly beyond code, I need 10.5 sqft of venting and I have 14 sqft
derekr,
I think Michael was saying that the underlayment doesn't make any difference. The flooring is already a vapour-barrier. Whether your floor is at risk depends on how humid it is, not whether there is underlayment or not.