by Professor Gene Wengert
I am trying to determine the acceptability of air drying rough sawn cypress siding lumber to use in a board and batten installation on a house. Is kiln drying necessary and/or better? Is air drying better or even acceptable at all? The green cypress is from Florida and will be used in a house in the Midwest.
Undried cypress can be used but there are two potential problems. First, in the kiln drying process we sterilize the wood, killing all insects, insect eggs, and fungi. As there is only one critter that likes dry wood, kiln drying offers considerable protection. However, the risk of damage in old-growth cypress is minimal.
Second, the wood will shrink after it is nailed in place (a 6 inch piece will shrink as much as 1/4 inch), creating gaps between the pieces that may not be totally covered by the battens.
Also, when the pieces shrink they can pull out the nails and/or may develop a cupping type of warp and curl of the wall in spots.
Professor Gene Wengert is Extension Specialist in Wood Processing at the Department of Forestry, University of Wisconsin-Madison.
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