Wood flooring is a hygroscopic material, which means that it is subject to dimensional change as a result of variations in moisture, temperature and humidity within the surrounding environment. Dimensional stability refers to how wood shrinks and swells in relation to moisture gain or loss. In other words, how a floor “moves” once it is installed.
The Dimensional Change Coefficient is a simple tool that can help installers predict what flooring may do when exposed to moisture change. The first step is to determine the species you will be installing; in this example we’ll use red oak. A red oak board experiences a moisture content change of 6 to 9 percent, a change of 3 percentage points.
Next, multiply that change in moisture by the change coefficient (chart to the right). The numbers in this chart were developed by the Forest Products Laboratory of the U.S. Department of Agriculture and reflect the Dimensional Change Coefficient for the various species.
Finally, multiply that figure by the width of the material. The result will give you a figure that should represent how much each board could shrink or swell when exposed to the change in moisture content.
3 (% change) x .00369 x 5” = .055”
It’s important to keep in mind, however, that this tool may only be used to determine approximate shrinkage and swelling based on change in environmental conditions. Remember, no two trees from the same species are exactly the same just as no two boards from the same tree will be exactly the same. The grain configuration also affects these values and varies within every board. Finally, in actual practice, change would be diminished in an installed floor since the boards’ proximity to each other tends to restrain movement.