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Proper seasoning and storage provide optimal dimensional
stability of lumber in service. To minimize shrinkage, SPIB
Grading Rules require dimension lumber 2" or less in
thickness be kiln-dried or seasoned to a moisture content not
exceeding 19%. This will result in an average moisture
content of about 15% at the time of manufacture. Additional
conditioning will take place when lumber is stored and used
as it adjusts to the moisture content of its end-use
environment. For interior items, such as flooring, millwork
and furniture, the end-use moisture content will average
between 6% in the dry Southwestern U.S. and 11% in the
humid U.S. Gulf South. For exterior items, such as framing,
siding and sheathing, the end-use moisture content will
average 12% in most areas of the U.S., with a range from 7%
to 14%.
Proper receiving, unloading, storage, handling, installation
and bracing of lumber after delivery will help maintain
material quality during construction and service life. Follow
these simple rules to help ensure proper storage and product
performance at the job site:
- Inspect lumber upon delivery for proper grade-marking and
moisture content, plus other conditions that may require attention,
such as mold.
- Unload lumber in a dry place – not in wet or muddy areas.
- Elevate lumber on stringers to prevent absorption of ground
moisture and to allow air circulation. Do not store lumber in direct
contact with the ground.
- Cover lumber stored in an open area with a material that will give
protection from the elements. Polyethylene or similar non-porous
materials act as a vapor barrier, so it is important to allow
ventilation around the material to prevent condensation on the
underside of the covering.
- Enclose framing lumber under roof as soon as possible.
- Store exterior patterns (e.g. siding, porch flooring) in a covered
outdoor area.
- Store interior items such as flooring, millwork and cabinets in
the enclosed conditioned area where installation will occur.
There is additional protection when lumber comes in
paper-wrapped packages or has been treated with a weatherprotective
coating. However, availability is limited and
weather-protective coatings are generally effective for only
about three to six months. Damage to the paper during
transportation can reduce its effectiveness, and protection is
lost when paper wrappings are removed. For additional
information, refer to the SPC publication Managing Moisture
and Mold.
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