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Proper storage techniques are essential to the efficient and economical use of lumber. Proper storage also:
- Helps protect lumber from mold, fungi decay, and insects.
- Helps prevent defects that result from alternate wetting
and drying.
- Helps maintain appearance and dimensional stability.
- Helps safeguard against costly callbacks.
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 radially to the
growth rings, and very small amounts occur longitudinally.
With the grain orientation shown in the figure to the right, 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%.
Refer to U.S. map below.
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 - it reduces warp, twist, stain and crook.
- Nail Popping - which results when wood shrinks, causing the
heads of nails to protrude. Spiral shank and annularly 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:
- 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, but be porous enough to allow
moisture to escape. Polyethylene or similar non-porous covers may
trap moisture.
- Enclose framing lumber under roof as soon as possible for
protection from the elements.
- Store exterior siding and finish in a covered, outdoor area.
- Store interior items such as flooring, millwork and cabinets in an
enclosed, conditioned area to maintain equilibrium moisture
content.
- Use lumber in the order in which it is received. Inventory rotation is
important.
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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