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Job Site Preparations for Hardwood Flooring Hardwood is a living substance which reacts to changes in relative humidity. Wood gains and loses moisture before and after installation, as surrounding conditions fluctuate. Indeed, wood expands in the summer when humidity level is high and contracts in the winter when the humidity level is much lower. To minimize the expansion or contraction of your hardwood floor, it is recommended that the building should be well ventilated and the relative humidity level maintained at 45% all year long. The building should be closed in with outside windows and doors in place. All concrete, masonry, sheetrock and framing members, etc. should be thoroughly dry before the flooring is delivered to the job site. In warm months the building must be well ventilated; during winter months heating should be maintained near occupancy levels at least five days before the flooring is delivered and until sanding and finishing are complete. Basements and crawl spaces must be dry and well ventilated. In joist construction with no basement, outside cross ventilation through vents or other openings in the foundation walls must be provided without dead air areas. A surface cover of 6 mil polyethylene film is essential as a vapor in crawl space construction. Because materials used to provide energy efficient structures
trap moisture in a residence, it may be necessary to delay delivery
and installation of flooring to allow the excessive moisture trapped
during construction to evaporate. The average moisture content of
framing members and sub-flooring should be below 12%-14% before
delivery of the flooring. Moisture contents above 12%-14% can cause
moisture related problems. Using a hygrometer, verify the sub-floor
(plywood) humidity level; it must not exceed 12%. If the humidity
level is too high, turn up the heat and open the basement windows
less than an inch. Recommended Tools and Materials
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