Hi,

Around the end of May of this year we had some white oak 2 1/4" flooring installed on the first floor of our house. Around half the floor already had white oak installed, and the rest was carpet which was ripped out and replaced. The wood acclimated to the house for maybe 5 days before being installed. The existing wood was refinished. We used a swedish finish for all the flooring. Maybe a month later (? didn't really take not of when it started) *all* the newly installed wood began cupping, uniformly across all the new wood, while the existing wood is still perfectly flat.

My installer says it must be due to moisture in the crawlspace, and I admit that our crawlspace could use some work -- the ground moisture barrier is coming up in places, some insulation is falling down, and the insulation was installed upside down (the vapor barrier is towards the ground instead of towards the floor) -- but it makes no sense why the existing wood flooring would remain perfectly flat while the new flooring is all cupping. There are areas where the new and old flooring is above the same crawlspace/foundation, but the new wood cups and the old wood doesn't.

We'd already been planning on redoing our crawlspace insulation and moisture barrier, and I suppose we should've done that before installing the new floor, but because this cupping is only affecting the new flooring I'm suspicious something else is going on.

Any ideas?

Old floors really don't move anymore. I can't really accurately explain why other than saying they are more acclimated, more dry, they have already expanded and contracted about as much as they ever will. (unless ofcourse some major water damage or something). New floor takes months tro ever really dry out the way it needs to. It sounds like the crawl space is the issue. You can't really properly acclimate flooring in a house in a situation like that. The subfloor will be way colder than the air is what acclimated in.

Vapor barriers don't ever work 100%. I find them rather useless most of the time unless a tar paper was used. I consider it more of a buffer than a prevention (if that makes sense) Although it's never good to have a cupped floor, it's still better than having your floor shrink. Cupped floor can always be sanded out, If it shrinks, your stuck with gaps. The only thing that could of maybe been done is wait 2 weeks after it was installed, but even then the climate changes are going to effect the floor way more with a crawl space so there wouldn't of been a guarantee.

So, going with the assumption that the crawlspace is in fact the issue, once the crawl space is taken care of (new vapor barrier, new properly installed insulation) how long should we let things sort of re-acclimate before refinishing the new flooring? Is it at all likely that once it dries out under there it would go back to being flat (or at least close) on its own?

Well unfortunately once flooring has cupped like that is doesn't go back down. I'd say once everything is fixed i would give it a month to make sure the subfloors are dry. The upside is usually once the floors have already cupped like that they don't usually cup much more than they already have.

Installers are supposed to check crawl spaces. Plus check the moisture content of subfloor vs MC of the new wood. I'd get a dehumidifier in there asap.

The old flooring may be cupped and sanded flat long ago. Because it always lives in a state of a gradient moisture imbalance, it does not crown.


Many old floors installed in the 1930 and 40s here are cupped if you look at the crawl space, but flat as can be inside the residence.


Another cause could be that the flooring was not acclimated properly. Letting it sit 5 days, is not acclimation. It could actually hurt you if the heater is running and the humidity is in the teens during acclimation.

Acclimation is a moisture content thing. Not a time thing.

I'd say stephen is right...the subfloor was to wet for the wood floor and when heat kicked on..moisture pulled and transferred to new floor..

My money says: if it is crawl space moisture, and it is fixed, the old flooring will crown.

Measure relative humidity with hygrometer in crawl space also in area where it is installed. Measure moisture content in both floors see if they are the same will need a moisture meter with insulated pins and if the difference between the top and bottom of the boards is 1% or more cupping will occur. In crawl space put pins in other wood and take readings if the wood is different species make the adjustments for accuracy.
Relative Humidity controls Moisture Content and moisture content inconsistent with installation see chart chapter 4 page 4 The Wood
Handbook. Wood subfloor no more than 12% or don't install until it is. 2 1/4" solid hardwood if 4% difference between subfloor and hardwood don't install. Every mfg guidelines state so. Did your installer have a moisture meter to determine proper acclimation or did he proceed after a few days. If he did the latter your result is understandable. Go online get your wood manufacturers installation instructions if you doubt this. Only definitive testing will provide your answer. Your installer should have checked all this prior to installing your wood.


Around the end of May of this year we had some white oak 2 1/4" flooring installed on the first floor of our house. Around half the floor already had white oak installed, and the rest was carpet which was ripped out and replaced. The wood acclimated to the house for maybe 5 days before being installed. The existing wood was refinished. We used a swedish finish for all the flooring. Maybe a month later (? didn't really take not of when it started) *all* the newly installed wood began cupping, uniformly across all the new wood, while the existing wood is still perfectly flat.

My installer says it must be due to moisture in the crawlspace, and I admit that our crawlspace could use some work -- the ground moisture barrier is coming up in places, some insulation is falling down, and the insulation was installed upside down (the vapor barrier is towards the ground instead of towards the floor) -- but it makes no sense why the existing wood flooring would remain perfectly flat while the new flooring is all cupping. There are areas where the new and old flooring is above the same crawlspace/foundation, but the new wood cups and the old wood doesn't.

We'd already been planning on redoing our crawlspace insulation and moisture barrier, and I suppose we should've done that before installing the new floor, but because this cupping is only affecting the new flooring I'm suspicious something else is going on.

Any ideas?[/quote]

So then he can have the whole thing sanded down once everything is said and done. I'd fix the crawl space and wait a couple seasons to see what happens.