Water covers over two-thirds of the Earth’s surface and is essential for all living things. But do water and hardwood flooring mix? In a word, no. Whether you already have hardwood flooring or are considering it for the future, here are some things every homeowner should know about moisture.
Moisture in Wood
As trees grow, they absorb water through the roots and carry it to the branches and leaves through vessels. When a tree is cut down, its vessels begin to dry and shrink, causing the wood itself to shrink. During the milling process, the wood is subjected to additional drying. Oak, for example, is dried to an average moisture content of 6%–9%.
Once the milling process is complete, the wood’s moisture content gradually changes over time as the wood acclimates to the changing conditions around it. In drier conditions, the wood’s moisture content decreases, typically causing the wood to contract. In moister conditions, on the other hand, the wood’s moisture content increases, typically causing the wood to expand.
Because the vessels run the length of the grain, wood flooring tends to contract and expand widthwise rather than lengthwise.
Moisture in the Home
Homes in the U.S. have an average moisture level ranging from 4% to 18%. (Note that average moisture level differs from relative humidity.) Moisture levels vary based on geographic location, time of year—higher in the summer, lower in the winter—and conditions in the home.
When wood flooring is exposed to moisture, the consequences can range from minor swelling of the seams between boards to major cupping or crowning.
Crowning in a solid wood floor. Note that the planks’ edges curve downward.
Cupping in a solid wood floor. Note that the planks’ edges curve upward.
Fluctuations in a home’s moisture level can also cause wood floors to buckle, crack, or squeak. Moisture-control systems—such as dehumidifiers in humid regions (coastal areas, etc.) or humidifiers in drier regions (Denver, etc.)—help stabilize moisture levels. If you own a summer- or winter-home, you should consider leaving the moisture-control system on when the house is uninhabited to help prevent these issues.
Common sources of moisture you should be aware of include: