Have you ever been near a frozen lake when the expansion crack begins? I can remember hearing the increasingly loud crackling sounds and then the momentous sound as the ice buckled into a jagged series of peaks running like a zipper across the lake. Well, water and ice aren’t the only aspects of nature that change form and shape with the changing temperatures: Many organic materials respond to fluctuations in humidity and temperature, and lumber is one of those organic materials. While wood movement may not be as dramatic as the expansion of ice on a lake, it can be disastrous to those who do not anticipate its arrival.
Understanding Seasonal Wood Movement
Seasonal fluctuations in temperature and humidity affect the moisture content of lumber and therefore cause movement. Wood fibers are like miniature straws that become enlarged as they fill with water and narrow as they dry. During the coldest parts of winter, wood is shrunken to a smaller size than it will be any other time; this is true for exterior as well as interior applications. Inside, the warm, dry air that provides comfort, also acts as a drying kiln; humidifiers help limit shrinking, but they cannot eliminate the winter dryness altogether.
Planning for Seasonal Wood Movement
In some ways, the extremes that come with winter make it easier to plan for movement: We know wood will move only out from here. Since you know that the paneling, siding, or flooring is narrower than it will be at any other point in the year, you can evaluate species specifications and calculate gaps based on movement percentages. (Flat-sawn boards should be considered with tangential numbers, while quartersawn or vertical grain boards should be figured using radial shrinkage numbers.) For smartphone users, The Woodshop Widget is a handy and reliable app compatible with both Android and iOS. Of course, charts are only guides, and planning for a little more than necessary can be wise.
Evaluating Risks of Winter Installation
When movement isn’t carefully considered, expansion will inevitably result in damage. While improper summer installations can produce unsightly gaps during the winter, the consequences of poor planning during winter can mean buckled floors, split countertops, or other nonfunctional surfaces requiring costly repairs. Even with thorough planning and calculations, winter provides a uniquely challenging time for installing wood, simply based on the hazards of working in uncomfortable conditions; when wood movement is carefully considered, though, a builder’s frustrations may be solved by a cup of hot coffee in front of a fireplace.
The lumber experts at J. Gibson McIlvain are always studying wood and the unique characteristics of each species that we carry. Feel free to discuss your winter projects with us, and we’ll be glad to help you evaluate the risks and make careful choices regarding installation.
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Photo credits: Top © Robert Cocquyt / Fotolia. Bottom © Michael Flippo / Fotolia.