Q: We are in the process of having a new home built in Bonita Springs, Fla., and have a concern about the trusses being delivered and sitting outside in the rain. Is the damp wood a potential problem?
A: It is inevitable during construction that some of the wood framing and decking will get wet before the home is "under roof." However, prolonged exposure to rain and sun should be avoided when possible.
Framing lumber generally arrives at the building site dried so that it has a moisture content of 19 percent or less. Wood that is to be used inside the home where it is subject to moderate heating and cooling changes needs to be between 8 and 13 percent moisture content. This generally includes wood used for doors and windows, wood trim and flooring and wood used in cabinets and furniture.
Wood trusses are part of the framing that forms the attic space, where temperatures will vary over a wide range depending on the outside temperatures. When the attic space is warm and dry, the framing lumber will lose some of the moisture it contains to the surrounding air through convection or evaporation. When this occurs the spacing between the cells of the wood will decrease and the wood will shrink. When the attic is cool or cold the lumber will absorb moisture, displacing the spaces between the cells, and the wood will expand.
The same is true for lumber exposed to the elements. Framing lumber that is soaked with rain will expand and when fastened in place with nails or clips the shrinkage of the lumber will cause cracks to form at ceilings and walls and nails may start to work loose from the drywall or paneling.
To avoid some of the shrinkage problems ask your contractor to cover the stored trusses when possible. If they are already soaked, place wood spacers between each truss for drying. The spacer allows air to flow across the surface of the wood for better drying. The spacer also prevents one truss from soaking the next truss by wicking moisture from truss to truss. The same can be said of framing lumber such as wall studs, floor joists or floor trusses or any of the various wood siding materials.
(Dwight Barnett is a certified master inspector with the American Society of Home Inspectors. Write to him with home-improvement questions at PO Box 268, Evansville, IN 47702 or send him e-mail at d.barnett@insightbb.com.)
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