How To Prevent Wood Floor Gaps


Customer calls and says that their wood/laminate floor gaps in the winter.

Wood floors gap in the winter.  Here is an informative web page that discusses this issue.  It isn't just because radiant heat is under the floor, it has to do with humidity and other factors.  Narrow boards are better than wide boards.

Engineered flooring is supposed to be more stable than solid wood. From a technical aspect, this should be true. But many engineered flooring manufacturers restrict the use of their products to a certain RH range. I’ve seen warranties that specify 35 to 55 percent RH or 40 to 60 percent RH as the acceptable range. If the flooring is exposed to conditions outside these ranges, the warranties are void. In my 30-plus years of experience dealing with indoor environments in the U.S., I don’t know any location that will consistently maintain those RH ranges. So using engineered flooring may be an option for reducing winter-time floor issues, but check the manufacturer’s recommendations and warranty.

Narrow boards will shrink less than wide boards for a given change in moisture content (MC). A 5-inch-wide plank will shrink twice as much as a 2¼-inch-strip. So the size of the gap between 5-inch boards will be twice as big as the gap between 2¼-inch boards. More joints means more places to distribute gapping.

Some species are more dimensionally stable than other species. For a given change in MC, a 5-inch-wide hickory plank will shrink more than a 5-inch-wide red oak plank. The U.S. Forest Service, and others, publishes dimensional change coefficients for different species. A second solution to excessive winter gapping is to use a species of wood that is more stable (one with a smaller dimensional change coefficient).

Along the same line of varying dimensional stability, quartersawn flooring shrinks about half as much as flatsawn flooring for the same amount of moisture change, so quartersawn flooring will have smaller gaps than flatsawn flooring under the same circumstances.

Therefore, from a wood standpoint, to have the smallest winter gaps, use quartersawn, narrow boards from a stable species.

Written by Scott Rosenbaum
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