Acclimating wood flooring before it goes in

Wood takes on and gives up moisture with the air around it, and it swells and shrinks as it does. Acclimating a wood floor, more accurately called conditioning, means making sure the flooring and the house it goes into are compatible before it's installed. It's measured with a moisture meter rather than counted in days. The flooring maker's instructions come first, and following them keeps the warranty intact.

The house has to be ready first

The flooring shouldn't be delivered, or installed, until:

• The house is closed in. Windows, doors, siding, soffits, roof, insulation and ventilation are all in place.
• The wet work is done. That includes concrete, masonry, plaster, drywall, texture, painting and power washing.
• The heating and cooling has run for at least 5 days. The system should hold the same conditions before, during and after the installation. A tight new house or a wet job can need longer.
• Temporary propane heaters are gone. Burning propane puts a lot of water into the air.
• The space underneath is dry. A crawlspace or basement shouldn't have standing water or high humidity.

The conditions it needs

For solid wood, the indoor air is generally kept between 30 and 50 percent relative humidity and between 60 and 80°F. Some regions run higher, around 45 to 65 percent, or lower, around 20 to 40 percent, and some flooring is made for those climates. For factory-finished flooring, solid or engineered, the maker's temperature and humidity requirements apply.

The moisture checks

• Before delivery. The installer records the room temperature, the humidity and the subfloor moisture.
• On delivery. The installer rechecks the room and takes moisture readings on at least 40 boards from several bundles for the first 1,000 square feet, and averages them. Boards with unusually high or low readings stay out of the floor.
• The subfloor. A wood subfloor gets readings in at least 20 spots for the first 1,000 square feet, including at least three per room. It should be no more than 4 percentage points wetter than strip flooring under 3 inches wide, or 2 points wetter than wider plank flooring. A concrete slab gets its own moisture test, with moisture control in place before solid wood goes down.

When the boards arrive at the moisture content the house will hold in normal living, and the subfloor matches, the floor can go in right away. When they don't, the installer can open the packaging and cross-stack the boards with spacers so air reaches every side. Imported and tropical species often take two to three times as long as domestic woods.

After the floor is down

Unfinished solid flooring is usually left 5 to 7 days to settle before it's sanded and finished, when the schedule allows. A floor glued down may need longer, following the adhesive maker's dry times.

An annotated example

What to do next

Finish the drywall, painting and tile before the flooring is delivered, and run the heating or cooling for at least 5 days beforehand. Ask the installer to give you the board and subfloor moisture readings in writing before the floor goes down.