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Expansion Spacing ("Washer Rows")

Wood is a hygroscopic material. When exposed to varying temperature and humidities, it will release or absorb moisture until it is at equilibrium with the surrounding atmosphere.

Maple floors in the United States experience moderate seasonal moisture content swings as a result of normal climate changes during the year. For example, in an average year, maple flooring in lower Michigan experiences a 3 percent to 4 percent variation in moisture content, depending on location. A 4 percent swing can translate just less than 1/32" of expansion/contraction for each 2 1/4" face-width board in a maple flooring system.

To ensure successful placement and performance, many contractors install intermediate expansion spaces at regular intervals across the surface to allow maple expansion as normal seasonal changes dictate. Intermediate expansion spacing (or "washer rows") is installed at the discretion of the flooring contractor based on flooring moisture contents at the time of installation and/or normal anticipated changes in moisture contents throughout the year. Although either 1/16" or 1/8" washers are commonly used, the 1/16" spacers require less movement of the flooring strips during expansion, and are less visually objectionable.

Please note that spacing and frequency of intermediate expansion spacing is directly related to the time of year that the flooring is installed, as well as the amount of acclimation time provided in the construction schedule. Until you have a firm construction timetable from the General Contractor, it is difficult to calculate the precise amount of expansion/contraction spacing that will need to be provided.

If you have additional questions, please contact MFMA's Technical Director at 847-480-9138.

Rev. February 2005

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