Herringbone Parquet FloorOne of the biggest advantages of hardwood floors is their extremely long life. Nearly any well-maintained hardwood product can last hundreds of years. That said, wood must be cared for. One of the biggest threats to the integrity of wood floors is moisture. Understanding the effects moisture has on wood will help you keep your floors looking pristine throughout their lifetime.

How Wood Reacts and Why

It is common knowledge that trees contain water when they’re alive, but many people don’t realize that wood also stores water after it is cut. Wood is hygroscopic, meaning that the fibers act like a sponge to absorb and release vapor into the surrounding atmosphere. As a result, wood floors, doors, cabinets, and furniture expand and contract as humidity levels rise and fall. If you’ve ever had a door that sticks shut one day but opens freely the next, the cause is most likely high levels of humidity. This movement is perfectly normal and occurs with all wooden objects to some degree.

Wood Species

Different species of wood are capable of retaining more water than others. Dimensional stability is the term often used to describe how much a given wood will expand and contract from environmental conditions. Thought should be given to the relative humidity of your home climate when selecting a wood species. What’s right for a home in Arizona may not be right for a home in Florida.

While a wood’s density will generally give you a fair idea of how stable it will be (with harder species offering greater stability), other factors influence this movement as well. Qualities particular to the cells of a given type of wood affect dimensional stability, as does the size of the plank. Quarter-sawn planks also generally experience less horizontal expansion than flat-sawn.

Knowing the dimensional stability of wood species will help you make informed product choices and aid in future maintenance. (The U.S. Department of Agriculture has created a useful matrix to help calculate stability, clearly explained here.) It is important to note, however, that no two pieces of wood are the same. Therefore, in addition to calculating the dimensional stability of wood materials prior to installation, care must be taken when installing those materials to prevent unwanted side effects later.


A conscientious installer will acclimate wood to its optimal climate – the temperature and humidity levels at which your home will normally be kept. It is best to run an air conditioner and maintain a steady temperature for four to five days prior to installation. Wood products should be unpacked and stacked in this space so that air can freely circulate around them. This allows humidity levels in the wood to equalize with the surrounding environment, minimizing expansion and contraction during installation.

When installing hardwood flooring, it is also important to leave a gap around the floor’s perimeter. This gap should correspond to your calculation of expansion and shrinkage, often half to three-quarters of an inch. This is usually covered with baseboard to conceal it and to prevent dust and debris from collecting within.


Poor planning, poor installation, and poor maintenance can all lead to unsightly, moisture-related problems that will compromise the integrity of your floor. Some of the most common are as follows:


If a space is too dry, planks will separate to the point that thin gaps will appear between them. While a small amount of this is to be expected, gaps that are too large are unsightly. They also become traps for dust and debris, making floors more difficult to clean. Additionally, gapped floors are less comfortable to walk on.

Cupping Cupping

If moisture levels are too high, cupping can occur. Wood planks become saturated and expand to their maximum capacity. Naturally, planks are fitted together tightly during installation. When they become fully saturated, the edges bend upwards, creating a U-shape down the center of the plank. (Notably, it is the width of the plank that expands and contracts most. While a similar problem called “buckling” occurs when floors curl upward lengthwise, this usually only results from major flooding.) Cupped floors are quite noticeable and create an uneven surface. If left too long, cupping can permanently damage wood planks.


Crowning occurs when floors have cupped and, in a short-sighted effort to correct this, the homeowner sands down the upturned edges. While sanding is a viable option if long-term cupping has warped the planks, this should only be undertaken once humidity levels have been normalized. If floors are sanded prematurely, when the planks contract, the result can be plank edges that are lower than the centers. This, too, can create noticeably uneven floors that are uncomfortable to walk on.

Preventing Moisture Issues

Obviously, if your wood floors are already installed, you have no control over wood species or installation methods (unless you wish to remove them and start over). But there are measures you can take to prevent damage to your floors.

Responsible Upkeep

This may seem obvious, but keep liquids off the floors. When cleaning, do not wet mop. Use a broom or dry mop instead, dabbed with a manufacturer-recommended cleaner if necessary. Refinish floors approximately every five years.

When spills occur, clean them as quickly as possible. Do not allow water to stand. In the event of flooding or major plumbing leaks, don’t panic. While these may cause superficial damage, chances are they can be repaired, provided all water is removed quickly. Use fans to speed up the drying process. Consult a qualified wood professional if repairs are needed.

Indoor Climate Regulation

The simplest yet most effective measure you can take to preserve the integrity of the wood in your home is to regulate temperature and humidity levels. A quality humidifier, dehumidifier, and air conditioner are modest investments that will help to prolong the life of your floors almost indefinitely.

The National Wood Flooring Association recommends that spaces be kept between 60 and 80 degrees Fahrenheit, with relative humidity levels between 30 to 50 percent. A moisture meter can be used to take regular measurements of the relative humidity of your space. (A handy set of guidelines can be found here.) Recording these measurements at regular intervals will streamline the process of climate regulation.

Houses most at risk for damage are those occupied only part of the year. If you’re a snowbird or have a summer home, be sure to take steps to ensure that the climate in your getaway is properly regulated. While this may add nominal expense in the short term, it will help maintain the integrity and value of your home for generations to come.