Q. What's the proper procedure for acclimating wood flooring to the moisture content of a building before installation?
A. Howard Brickman, a wood-flooring contractor and consultant in Norwell, Mass., responds: One of the enduring myths of the wood-floor business is that you can prevent swelling and shrinkage problems if you just let the flooring acclimate for x days before installation (supply your own value for x).
In fact, though, the first consideration is to manage the moisture content of the job site itself. Especially with new construction, the key is to make sure that excess moisture - from curing concrete, from less-than-dry framing lumber, or from rain or snow that may have soaked the structure before the roof was on - is removed before the wood flooring is even delivered.
The best way to determine whether the site is dry enough is to measure it with a pin-type moisture meter. The moisture content of the subflooring should not exceed 11 percent in the northeastern U.S., 14 percent in the humid Southeast, and 9 percent in the arid regions of the West. In western coastal regions, the acceptable subfloor moisture content will vary from about 11 percent to 14 percent, depending on the local microclimate.
The moisture content of the flooring itself should ideally be 3.5 percentage points lower than that of the subfloor - or 7.5 percent in the Northeast, 10.5 percent in the humid Southeast, and 5.5 percent in the arid regions of the West. (To verify these values, you may want to measure the moisture content of a few three-year-old or older floors in your own area that you know look good throughout the year.)
Most solid wood flooring is manufactured at a moisture content of 7 percent, but - just as with subflooring - the actual figure should be determined with a moisture meter. If the numbers show that the flooring does need to be acclimated - hardwood with a moisture content of 7 percent, for example, should be brought up to 10.5 percent before installation in a humid climate - it should be unboxed and laid out directly on the subfloor until its moisture content, as measured with the meter, reaches the proper level.
