Why Oak Flooring Planks Cup and Other Misbehavior

Oak Flooring, Cupping and Moisture

Properly dried and manufactured oak plank flooring should be stress free and contain a moisture content between 6-9%. That’s the industry standard. But, that’s not suitable for every installation. Some environments require flooring that has a higher or lower moisture content. And, since oak flooring is hygroscopic, it will adapt to that different environment. The trick is to make sure that adaptation is accomplished prior to the installation! That’s where acclimation comes in. The environment in which oak flooring will be installed should be checked for two types of moisture content – that in the subfloor and that in the air. The relative humidity of the air should be in the neighborhood of 35% to be most comfortable for human habitation. It turns out that that’s perfect for an oak floor. And, the subfloor should be no more than a percent or two different than the oak flooring. If either are out of sync, the flooring installation must wait until they are in compliance. What can go wrong if I can’t wait? Lots.

How Moisture Effects Oak Flooring

Although, nothing will happen that is structurally dangerous – except in extreme cases – the result can be unsightly and uncomfortable. Cupping of the flooring planks (when their edges rise) and crowning (when their centers rise – or edges recede) are the two most common misbehaviors – and, will look bumpy and feel ridged underfoot. The cause of both conditions is an imbalance in moisture between the planks themselves and either the subfloor or the air above the planks – after installation. If the subfloor is wetter than the flooring planks, the planks will begin absorbing that moisture and their bottom surface will expand – or, if the air above the planks is drier than the planks, the top surface will begin to contract. Both of these conditions will cause the flooring to “cup”. Conversely, if the subfloor is drier than the oak flooring planks, the bottom of the planks will begin to shrink as they lose moisture – or, if the air above the planks is too humid, the upper surface of the planks will begin to expand – causing the flooring to “crown”. The good news is that both of these problems can be avoided if a thorough investigation and proper acclimation is conducted prior to the installation.

Oak Flooring and Moisture After Installation

But, what if something happens that causes these issues to occur later in the floor’s life? Whether from a dishwasher leak or some other environmental change, floors can suddenly deform years down the road. There’s good news there, too. The same cellular structure that would cause the flooring to absorb unexpected moisture, will also expel that moisture over time and if left alone, will allow your oak flooring to return to its original size and shape more often than not. So, all in all, an oak plank floor is your best bet for a lifetime of enjoyment.