by Professor Gene Wengert
Q.
What relative humidity should I maintain in my plant?
A.
The quick answer is: The relative humidity (RH) in your plant should match your customer's home or office. To explain further - Most homes and office in the U.S and Canada average 30% to 40% RH--drier in the winter, especially in colder climates; more humid in the summer, especially in warmer, coastal climates. As shrinking of a product is often much worse than a little swelling, we target the lower RH values. Hence, 6 to 7% MC for lumber is the target; 35% RH is the other target. An electric moisture meter can be effective for measuring MC. A brass, office-style RH indicator is no good--look for a good electronic device and then get several so you can check them against each other to make sure that they are working okay. If you humidify your shop or plant too high, you will just postpone the inevitable shrinkage problems until the customer gets the product.
Professor Gene Wengert is Extension Specialist in Wood Processing at the Department of Forestry, University of Wisconsin-Madison.
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