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Flooring 101

Winter and Wood Floors

By Tim Fowler

Winter in northern, mountain and central areas brings more than the freezing temperatures.

As the atmosphere cools down, the air loses moisture. Cold and arid days push outdoor humidity levels into the single digits causing days or even weeks to be at 20% RH or less. Consequently, we turn on the heaters and fireplaces, creating dry indoor conditions.

With low humidity outdoors and indoors, is it possible these conditions are drier than the Sahara Desert?

It is – the average humidity in one of the hottest places on earth is only 25% according to this reference.

For areas that are dry and cold during the winter, if you don’t increase your home’s humidity, you could be living in a drier environment than the Sahara. And these are no conditions for a hardwood floor!

Ever considered why there are so few trees in the Sahara? Trees need to absorb moisture from their surrounding environment. When the environment is dry, trees release moisture. As this happens, wood contracts from losing moisture. In humid environments, the tree will absorb moisture and expand.

Same thing happens with wood floors!

When wood floors get wet, they get wider. When they dry out, they retract. This seasonal expansion and contraction cycle is a natural process mimicking trees.

And when they’re Sahara Desert dry, you’re bound to have problems. Keep reading for why winter and wood floors can be a problmetic pair.

What Happens When Floors Are Dry

Dry floors create a variety of problems:

Boards shrink, resulting in narrower widths than when installed.
Narrowing boards leave gaps.
Dry cupping: floors can appear rippled or wavy at the edges.
Loose boards and gaps cause boards to squeak.

Fastener stress can cause squeaks. Flooring installed in the summer when humidity is high can later shrink to a greater degree during winter.

Floors that shrink exert greater pressure on the fasteners, pulling the nail or staple away from the subfloor. Squeaks occur when walking on these loose boards rubbing together.

What is Dry Cupping?

One of the most common symptoms of a too dry floor, cupping boards occur when there is an imbalance of moisture between a board’s surface and bottom side. To put it simply, the top side is drier than the bottom side.

Before a board becomes flooring, the lumber is dried. This process creates dimensionally stable flooring with consistent moisture content. However, this stability is not a guarantee. Any extreme changes in temperature and humidity will upset this equilibrium.

Flooring that becomes wetter than its original acclimated state will curl at the edges. When this occurs in winter, it is called “dry cupping”. The surface layer is drier than the bottom layer against the subfloor.

Damage can range from subtle to significant, depending on the amount of moisture or lack of it in the boards. In either case, the raised edges will be visually bothersome. If not addressed, the damage leads to squeaks, crackles, and pops.

What About Engineered Wood Floors?

Solid and engineered wood floors react differently to moisture changes.

Engineered wood flooring is more dimensionally stable because of its design. Engineered floors are constructed with a real wood wear layer glued to plywood. This style of wood floor can better perform where moisture may be a concern.

But, a little-known disadvantage for engineered flooring is an extremely dry climate.

In these Sahara-like conditions, the wear layer may loosen from the plywood layer. The veneer wood fibers shrink and then tear away from the adhesive, causing board failure.

And really, it’s preventable by keeping humidity at a level between 35-55%.

A consistent environment in the home is the best way for wood – solid or engineered – to keep its beautiful appearance. Deviating outside the recommended range of the flooring manufacturer can lead to failure.