| PROPER LUMBER STORAGE Using proper storage techniques is essential to the efficiency and
economical use of lumber. Proper storage also:
- Protects lumber from fungi and insects.
- Prevents defects that may result from
alternate wetting and drying.
- Helps maintain appearance and dimensional
stability.
- Helps to safeguard against costly callbacks
for builders.
Dimensional Stability
Proper seasoning and storage helps provide optimal
dimensional stability of lumber in service. Wood is composed of a series of organic cells
that contain water and act similar to a sponge. As water is removed from the wood fiber,
it shrinks; conversely, if submerged in water, it swells. The greatest shrinking and
swelling occurs tangential to the growth rings, while half as much occurs tangential to
the growth rings, and very small amounts occur longitudinally. With the grain orientation
shown in the figure below, the depth of the joist will increase or decrease the most with
moisture content changes.
To minimize shrinkage, Southern Pine grading rules require
that 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 15%.
Additional conditioning will take place as lumber is stored, or used where it will reach
equilibrium moisture content. For interior items such as flooring, millwork and furniture,
the moisture content will average between 6% and 11%. (See U.S. map.)
Average moisture content for interior wood products.
For exterior items such as framing, siding and sheathing,
the moisture content will average 12% in most areas of the U.S., with a range of 7% to
14%.
Proper storage helps maintain dimensional stability before
and after delivery to the job site. It is a safeguard against costly and unsightly
problems such as:
- Warp, etc. - it
reduces warp, twist, stain and crook.
- Nail Popping -
which results when wood shrinks, causing the heads of nails to protrude. Spiral shank and
annually grooved nails also help to prevent this problem.
- Baseboard Pull-Away
- which occurs when floor or ceiling joists are installed with excessive moisture content.
As the lumber shrinks, the floor or ceiling is pulled away from mouldings.
Job Site Storage
Regardless of where lumber is stored at the job site, a few
simple precautions should be observed:
- Lumber should be unloaded in a dry place -
not in water or muddy areas.
- Lumber should not be in direct contact with
the ground. It should be elevated on stringers to allow air circulation.
- Lumber stored in an open area should be
covered with a material that will give protection from the elements but be porous enough
to allow moisture to escape. Polyethylene or similar covers may not allow the passage of
moisture.
- Framing lumber should be enclosed and under
roof as soon as possible for protection from the elements.
- Exterior siding and finish should be stored
in a closed unheated area.
- Interior items such as millwork, flooring,
and cabinet work should be stored in a closed area where heat can be applied during damp
weather to maintain the desired moisture content.
- Stock rotation is important when dealing
with large deliveries. Lumber should be used in the order in which it is received.
The builder, building contractor, licensed contractor,
erector or erection contractor is responsible for the proper unloading, receiving,
storage, handling, installation and bracing of lumber at the job site.
There is additional protection when lumber comes in
paper-wrapped packages or has been treated with a weather-protective coating. However,
availability is limited and weather-protective coatings are effective for only about three
to six months. When paper wrappings are removed, protection is lost.
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