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Douglas Fir (Pseudotsuga menziesii) is not a true fir at all, nor
a pine or spruce. It is a distinct species named after Archibald
Menzies, a Scottish physician and naturalist who first discovered
the tree on Vancouver Island in 1791, and David Douglas, the Scottish
botanist who later identified the tree in the Pacific Northwest
in 1826. The species is known by a number of common names including
Oregon Pine, British Columbian Pine, Red Fir and even Douglastree;
however, the U.S. Forest Service settled on Douglas Fir some years
ago. Douglas Fir is North America's most plentiful softwood species,
accounting for one fifth of the continent's total softwood reserves.
Western Larch (Larix occidentalis), sometimes called
Mountain Larch or Western Tamarack, was discovered in 1806 in western
Montana. However, it remained for the botanist Thomas Nuttall to
recognize and describe the tree as a previously unclassified species
in 1834. It is one of only three conifers that sheds its needles
in the winter, with new needles developing in spring. Western Larch
is native to eastern Oregon and Washington, Idaho, Montana, and
southern interior British Columbia. Like Douglas Fir, it is among
the strongest and hardest softwood species.
| Douglas Fir timberlands* are the
most productive softwood timberlands' in the U.S. in terms of
volume per acre. More softwood lumber is produced in Oregon
than in any other state due in large part to the predominance
of Douglas Fir in its coastal forests. Known as the "timber
basket," where systematic replanting has been documented
since 1912, the northwestern region is governed by some of the
world's toughest environmental laws providing protection for
habitat, watersheds, soils and biological diversity, thus fostering
a multiplicity of forest values in perpetuity. Reforestation
and management practices are not voluntary, they are enforced
by law. |
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(*Timberland
is forested area producing or capable of producing crops of
industrial wood and not withdrawn from timber utilization by
statute or administrative regulation. Any reference to standing
volumes of sawtimber or acres of multiple-use timberland available
for timber products in this text do not include any of the forested
land that is permanently set aside, protected from harvesting.)
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In the West, timber for products is managed primarily
in natural stands, on long rotations. There are approximately 34.6
million acres of Douglas Fir managed primarily in natural stands.
Although production is much greater in Douglas Fir, the two species
account for more than 45 percent of all Western softwood produced
annually.
Each year, more than 1.5 billion tree seedlings are
planted in the U.S. -- some five new trees for each American. Nationally,
annual forest growth has continually exceeded harvest since the
1940s. In the West, forest growth exceeds harvest by 35 percent
or more each year.
Douglas Fir lumber products are identified by region.
Products from trees growing west of the Cascade Crest to the Pacific
Ocean, the most abundant region for Douglas Fir, are simply identified
as "DF" on the grade stamp. East of the Cascades, Western
Larch grows intermixed with Douglas Fir. The two species are often
kept separate in appearance grade products but are combined in Dimension
products and marketed as "DF-L". Because Douglas Fir and
Western Larch share nearly identical structural characteristics
and physical working properties, the two species are interchangeable
in Dimension products.
A smaller volume of products originates from Douglas
Fir growing in Arizona, Colorado, Nevada, New Mexico and Utah. These
are identified on the grade stamp as Douglas Fir-South or "DFS".
Douglas Fir grown in Canada is identified as Douglas Fir North or
"D Fir (N)" as shown on the grade stamp.
| Douglas Fir and Western Larch lumber
users may look to the registered grade mark of the Western Wood
Products Association (WWPA) for quality, accountability and
performance assurance on lumber produced from the Western Woods
region. |
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WWPA is the leading association of lumber manufacturers
in the West and one of the largest lumber trade associations in
the world. WWPA is the only lumber agency in the U.S. recognized
by the Japanese Ministry of Agriculture, Forestry and Fisheries
(MAFF) as a Registered Foreign Certification Organization (RFCO)
and is authorized to certify mills and provide quality control supervision
for gradestamping to Japanese Agricultural Standards: JAS 600-Japanese
Dimension Grades, JAS 702-Japanese MSR grades, and JAS 143 & JAS
1842/1892-Japanese traditional post-and-beam construction grades.
In addition, WWPA gradestamped National Grade Rule (NGR) Dimension
lumber is recognized by the Japanese Ministry of Land, Infrastructure
and Transportation (formerly Ministry of Construction) for use in
wood-frame construction.
WWPA is an approved Certification Body under the United
Kingdom (UK) Timber Grading Committee. Therefore, WWPA gradestamped
MSR lumber, NGR Dimension lumber, WWPA Heavy Timber grades and UK
structural grades are accepted for use in timber construction in
the UK and many other European countries.
As wood loses or gains moisture, it will shrink or
swell until it reaches equilibrium with the constantly changing
level of moisture in the air of its immediate environment. All lumber
benefits from some degree of "seasoning," i.e. letting
it adjust to the humidity conditions of its surrounding atmosphere
before it is installed. Because of its cell structure, wood shrinks
primarily in width and thickness and very little in length.
Douglas Fir is unique among all softwood species in
that it is naturally dimensionally stable, having the ability to
season well in position. Many builders prefer to cut, nail and fasten
Douglas Fir in the "green" or unseasoned condition, allowing
it to air dry during construction. As a result, coastal Douglas
Fir structural lumber is often shipped unseasoned (indicated by
S-GRN on the grade stamp). Framing lumber 2 inches and less (nominal
size) in thickness can be shipped after seasoning to a moisture
content of 19 percent or less, which is indicated by S-DRY, KD or
KD-HT on the grade stamp. S-DRY can mean kiln dried or air seasoned,
while KD and KD-HT specifically mean kiln dried. Regional market
conditions and building trade preferences dictate local availability
of dry or green products.
For millwork, remanufacturing applications or glued
products, Douglas Fir is dried in temperature and humidity-controlled
kilns or stacked and air dried until its moisture content (MC) reaches
the desired level for an intended purpose.
The term "DRY" can be confusing in lumber
terminology. In structural grades, "DRY" indicates a product
was either kiln- or air-dried to a 19 percent or less moisture content
level prior to surfacing. However, in appearance products (e.g.
the FINISH and SELECT grades), "DRY" is defined in the
Western Lumber Grading Rules as being a maximum of 15 percent
MC and in these grades, 85 percent of the items will be shipped
with a MC level of 12 percent or less.
(For additional information refer to WWPA's
Western Lumber Product Use Manual, Natural
Wood Siding Technical Guide, Lumber Storage
TIP sheet, and Dimensional
Stability publications.)
Grading
 The
WWPA grade stamp assures conformance of the graded piece with its
applicable WWPA Western Lumber Grading Rules. WWPA is an
accredited lumber rules-writing and grading agency of the American
Lumber Standard Committee, Inc. (ALSC) under the jurisdiction of
the U.S. Department of Commerce. The Association is certified to
grade and inspect lumber according to its own Western Lumber
Grading Rules, and also to the West Coast Lumber Inspection
Bureau's (WCLIB) West Coast Lumber Standard Grading Rules,
the Pacific Lumber Inspection Bureau's Export R List Rules,
the National Lumber Grading Authority's (NLGA) Standard Grading
Rules for Canadian Lumber, the Redwood Inspection Service's
(RIS) Standard Specifications for Grades of California Lumber
and the Southern Pine Inspection Bureau's (SPIB) NGR and Scaffold
Plank portion of the Standard Grading Rules for Southern Pine
Lumber. These rules provide lumber users with a dependable measure
for determining the quality and uniformity of lumber as well as
its performance capabilities.
Lumber grades, assigned on the basis of visual inspection
and/or mechanical testing, are divided into three basic classifications
which reflect the intended end uses:
Structural lumber for residential,
commercial and industrial uses is graded for its performance in
load bearing or load-carrying applications. Physical working characteristics
are the primary considerations and appearance is secondary. These
products are typically gradestamped with the following information:
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Registered trademark or logo of WWPA;
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Mill name or mill number identifying the origin
of the product;
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Moisture content designation at the time of surfacing;
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Species or species combination; and
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Grade name.
Appearance grades are assigned to
lumber intended for applications where appearance is the most important
factor. These grades cover products ranging from the exquisitely
beautiful to the most utilitarian. They may be sold as SELECTS,
FINISH or COMMON boards, run-to-pattern for siding and paneling
products, or used for a variety of purposes. The grades of appearance
products are often certified by written documentation rather than
marked on the lumber. Some products may be identified or gradestamped
on the back side or ends, but the highest grades are rarely stamped
to avoid marring the beauty of the wood.
Factory and Shop grades are assigned
to lumber intended to be recut, to recover the clear portions in
the piece for manufacturing into other wood products such as windows,
doors and cabinets, and for moulding, trim and specialty products.
While there are special categories within each of
these broad classifications, nearly all lumber grades fall within
them. Douglas Fir products are available in all three classifications,
Western Larch is available in structural and appearance grades,
and many Douglas Fir products are available in special grades and
sizes for international markets.
Characteristics and attributes
 When
architects and engineers look for the best in structural lumber,
their first choice repeatedly is Douglas Fir. It is dimensionally
stable and universally recognized for its superior strength-to-weight
ratio. Its high specific gravity provides excellent nail and plate-holding
ability. The species also enjoys a documented superior performance
against strong forces resulting from natural phenomena such as winds,
storms and earthquakes. It is truly the ideal structural and general
purpose wood for framing lumber in residential, light commercial,
multistory and industrial construction.
The Douglas Fir/Western Larch species combination
has the highest modulus of elasticity (E or MOE) of the North American
softwood species. This is the ratio of the amount a piece of lumber
will deflect in proportion to an applied load; it is a reflection
of the species' high degree of stiffness, an important consideration
in the design of floors and other systems.
In strength properties, Douglas Fir/Western Larch
has the highest ratings of any Western softwood for extreme fiber
stress in bending (Fb); for tension parallel-to-grain (Ft); for
horizontal sheer (Fv); for compression perpendicular-to-grain (Fc);
and for compression parallel-to-grain (Fc//).
These physical working properties, as well as to the
moderate durability of its heartwood and its excellent dimensional
stability, provide the reasons many builders use Douglas Fir as
the standard against which all other framing lumber is judged. It
is also tight knotted and close-grained, adding the bonus of beauty
to its structural capabilities.
(Refer to WWPA's Product
Use Manual and Western Lumber
Span Tables for additional design information and to WWPA's
Vol.1 Species Book: Dimension Lumber for color photographs of structural
grades.)
Dimension Lumber
Dimension lumber structural grades include surfaced
softwood products of nominal thickness from 2 inches to 4 inches
in thickness by 2 inches and wider. These grades are intended for
use as general framing members, including beams, joists, planks,
rafters and studs.
The National Grading Rule for Dimension Lumber, published
in the grading rules of all ALSC-accredited rule-writing agencies,
classifies Dimension lumber into several basic size categories related
to intended end uses. Products are available in a variety of lengths,
beginning at 6 feet and increasing in multiples of 2 feet.
2x2 through 4x4:
Structural Light Framing grades in
2x2 through 4x4 of Douglas Fir and Western Larch fit applications
where the highest design values are needed in light framing sizes
for engineered systems, trusses and multistory projects.
Light Framing grades in 2x2 through
4x4 are the building stalwarts of residential and light commercial
construction. These grades are well suited for general framing applications
such as wall framing, plates, sills, cripples, blocking, etc.
STUD grade is the backbone for most
interior and exterior wall framing. Characteristics affecting strength
and stiffness values are limited, making STUD grade products perfectly
suited for vertical uses such as load-bearing walls. Douglas Fir
and Western Larch studs can be manufactured to the full basic length
and double-end trimmed or may be precision-end trimmed to exact
length. Some WWPA Member companies produce "wane-free"
studs.
2x5 through 4x18:
Structural Joists and Planks is a
category of Dimension lumber products (2x5 through 4x18) intended
to fit structural applications for lumber 5 inches and wider, such
as floor joists, ceiling joists, roof rafters, headers, small beams,
trusses and general framing. Because of its structural performance
benefits, which rival many fabricated products, dry Douglas Fir
is also often selected for horizontal framing in multistory wood-frame
buildings. Its combination of high Fb and MOE values make it ideal
for floor framing when stiffness is a critical factor.
Large sizes
Douglas Fir is one of the few species available in
large sizes from managed timberlands. It is preferred for heavy
timber framing and large members are available in a variety of grades
manufactured for construction uses where larger material is needed
to meet the engineering requirements of the design.
Beams & Stringers include products
that are 5 inches and thicker (nominal) with a width more than 2
inches greater than the thickness (i.e., 6x10, 8x12, etc.).
Posts & Timbers are 5 inches
x 5 inches and larger (nominal) with a width not more than 2 inches
greater than the thickness (i.e., 6x6, 6x8, etc.).
Douglas Fir timbers are best known for their tough
fiber, dense grain structure and strength. They are additionally
valuable for their rustic beauty and excellent "Heavy Timber"
fire ratings in the model building codes. Timbers are shipped unseasoned
and may be specified rough cut or surfaced four sides (S4S).
Engineered Lumber
Machine Stress-Rated (MSR) lumber
Machine Stress-Rated (MSR) lumber is distinguished
from visually stress-graded Dimension lumber in that each piece
is nondestructively tested with mechanical stress-rating equipment
to measure its stiffness and other physical working properties before
it is subjected to visual inspection. Standard sizes are 2 inches
and less in thickness and 2 inches and wider with lengths 6 feet
and longer in multiples of 2 feet.
The grade stamp on MSR lumber indicates the machine
stress-rating system used meets requirements of the grading agency's
certification and quality control procedures. The grade stamp includes
the phrase "Machine Rated" along with the E and Fb ratings.
The stamp will also include the allowable tensile stress parallel-to-grain
(Ft), the horizontal shear (Fv) or compression perpendicular-to-grain
(Fc) design values when any of these properties are specifically
qualified. WWPA is one of the leading agencies certifying MSR lumber.
(Refer to WWPA's MSR Lumber
TIP Sheet for additional information.)
Truss and component applications
 Douglas
Fir MSR lumber is often selected for metal plate-connected trusses
and other engineered applications. However, it is also used for
floor and ceiling joists, rafters and other structural purposes
where mechanically assessed strength and connection capabilities
are primary considerations. MSR lumber is available both seasoned
and unseasoned.
Douglas Fir and Western Larch, in both visual and
MSR grades, are used in roof and floor trusses, for gable ends and
wall panels, pre-cut wall framing packages, wall sub-components,
corners, doors, beams and frames. The exceptional stiffness, strength-to-weight
ratio and plate-holding superiority are well recognized by component
manufacturers.
Structural-glued lumber products
Western manufacturers produce a variety of Douglas
Fir/Western Larch glued products from dry and unseasoned lumber,
including end-jointed or finger-jointed lumber, end- and edge-glued
boards, millwork and mouldings, face-glued lumber and laminated
stock. These products make excellent use of short lengths, increasing
utilization of available timber resources.
Structural-glued Dimension lumber has gained wide
acceptance in the building and construction industry. It has been
accepted for use under all model codes and is interchangeable with
solid-sawn Dimension lumber of the same size, grade and species.
WWPA provides testing and quality control inspections for glued
products and certifies the manufacture of Douglas Fir and Western
Larch structural-glued Dimension lumber under the following classifications:
Light Framing and Studs, Structural Light Framing, Decking, Stress-Rated
Boards and Structural Joists and Planks.
(Refer to WWPA's Structural
Glued Lumber TIP Sheet for additional information.)
Stock for laminated beams
Structural performance is the hallmark of Douglas
Fir, but the species is also visually beautiful. When a design calls
for large beams, long spans or unusually shaped arches as in churches,
bridges and stadiums, Douglas Fir is often specified. Structural-glued
laminated Douglas Fir and Western Larch beams are engineered for
use as load-carrying horizontal framing for roofs, floors and columns
in residential, commercial, industrial and institutional structures
as well as for towers and marine installations. These glu-lam beams
can be depended upon in industrial plants, warehouses and factories,
as well as in highly visual architectural settings that demand uncompromising
beauty.
Laminating stock is 2 inches and thinner and 3 inches
and wider and comes in five grades. It's also available as E-Rated
structural laminations, which meets the visual grade requirements
of L3 or better structural lamination grades and is mechanically
tested for long-span flatwise modulus of elasticity (E). Structural
laminations are specified rough or surfaced at various widths and
thicknesses up to 2 inches full. The wood is intended to be laid
up longitudinally and bonded with adhesives.
Structural decking/subflooring
Structural decking is 2 inches to 4 inches thick by
4 inches and wider. This is primarily an industrial or residential
or commercial roof or floor product and should not be confused with
grades intended for exterior residential decks. It is available
in two grades: SELECTED DECKING (for fine visual aesthetics) and
COMMERCIAL DECKING (when appearance is not of primary importance).
Both grades can be used so that the face, or better side, will show
the beauty of the wood, such as in exposed ceilings. Decking is
manufactured either at 19 percent (S-DRY, KD, or KD-HT) or 15 percent (MC15 or
KD15) moisture content.
Standard decking patterns, in nominal 2 inches single
tongue-and-groove (T&G) and 3 inches and 4 inches double T&G, are
available with "V" or rounded edges, striated, grooved
or in other patterns to meet discriminating architectural requirements.
Douglas Fir factory floors, manufactured from dry
decking, result in a smooth, even surface so hand trucks won't hang
up and cracks and splintering won't appear after heavy and continuous
use.
Some T&G decking is manufactured to pattern from NO.
2 & BTR or NO. 3, 2x6 or 2x8, S-GRN framing lumber. These products
are generally used for concealed residential subfloors in crawl-space
construction.
Characteristics and grades
 For
versatility and beauty, few woods in the world match the magnificence
of Douglas Fir and Western Larch. Unlike the structural grades,
appearance lumber is milled and graded according to aesthetic rather
than structural performance criteria. Color, grain pattern, texture,
knot type and size are the factors that influence the grade. For
this reason Douglas Fir and Western Larch are usually separated
in the appearance grades and marketed as distinct species to allow
a larger range of visual choices for discriminating end users.
Douglas Fir's light rosy color is set off by its remarkably
straight and handsome grain pattern. While similar, Western Larch
is slightly darker in color. Of the two species, Douglas Fir is
more widely available in the appearance grades. Both species will
"redden" over time when exposed to light. Their tough
fiber make both species difficult to work with hand tools. However,
both respond admirably to sharp power tools and machine to an exceptionally
smooth, glossy surface. Both paint easily and can hold all types
of stains and finishes.
Moisture content levels are carefully controlled in
the highest grades to ensure these premium products will meet the
strict dimensional stability requirements of finish carpenters,
furniture manufacturers and cabinet makers. The less "perfect"
grades are an economical choice for many utilitarian applications.
Many designers and consumers agree the aesthetic appeal
of clear, light, straight, vertical-grain Douglas Fir is unsurpassed
among the world's softwood species. However, the highest appearance
grades of Douglas Fir and Western Larch are manufactured from trees
older than those which yield primarily structural framing products.
And while substantial volumes of clear and nearly clear Douglas
Fir are available from long-rotation, managed western timberlands,
the clear grades are less abundant and considerably more expensive
than knotty grades
(Refer to WWPA's Vol. 2 Species Book: Boards and
Commons for additional information and color photographs of appearance
grades in a variety of Western species.)
Interior and exterior trim, and Finish board materials
Appearance and dimensional stability are critical
in interior and exterior trim and finish boards, whether in the
clear or knotty grades. Douglas Fir's characteristics make it ideal
for joinery: doors, millwork, window and door casings, mantels,
stairs and baseboards. When dry, it retains its shape and size and
won't check or show a raised grain. Additionally, Douglas Fir has
an excellent performance record when used in exposed applications
for exterior trim without ground contact.
(Refer to the "TREATED PRODUCTS" section
for in-ground and ground-contact information.)
Clear and knotty grades
The highest grade categories, "Finish" and
"Selects," include the grades for clear and nearly clear
lumber in either vertical or flat grain. (If grain pattern is not
specified, these grades will be shipped as a mixed grain combination
of vertical and flat grain.) Finish and Select grades of Douglas
Fir are recommended for interior trim and cabinet work with either
natural, stain or enamel finishes where the finest appearance is
important.
Douglas Fir "Commons" (WWPA Rules) or "Alternate
Boards" (WCLIB Rules) are typically used for shelving, sheathing
or run-to-pattern for siding and paneling. These products are nominal
1 inch thickness, surfaced to 3/4, inch and are generally gradestamped
on the back or ends.
The highest grades are used where fine appearance
in a knotty material is required, such as for soffits, fascia, cornices,
shelving or run-to-pattern for siding and paneling. Depending on
the criteria for the application, other grades in knotty products
are used primarily in housing and light construction where wood
is exposed for its beauty and character (e.g. shelving, paneling,
siding, fences, boxes) or for its utility and serviceability in
crating, subfloors, roof and wall sheathing and concrete forms.
The lowest grades are useful in applications where economy is the
basic requirement.
Wood paneling, cabinets and furniture
Designers appreciate the rich visual quality of Douglas
Fir texture and grain as well as its beautiful response to fine
craftsmanship and finishing. A favorite wood for custom cabinets,
furniture and millwork, it works easily and resists wear. When sawn
to expose vertical grain, doug-las Fir is particularly handsome.
Douglas Fir paneling can transform any room into
a dramatic, elegant space. The wood's fine appearance is clearly
visible in a variety of applications such as edge-grain veneers
for formal wall paneling or solid plank paneling for an informal
look. When acclimated prior to installation, Douglas Fir retains
its shape and size without shrinking, swelling, cupping, warping,
bowing or twisting. The uniform grain and tough fiber holds stain
well and keeps fasteners firmly in place.
Douglas Fir (and Western Larch to a lesser extent)
paneling is run in a variety of patterns. In many cases, the grade
of the patterned material reflects the grade of the starting material,
adhering to similar requirements for allowable characteristics.
Grades for paneling include the finish grades for highest appearance
and the Commons or Alternate Board grades for knotty products
(Refer to WWPA's Standard
Patterns for dimensioned, scaled profiles of standardized WWPA
siding and paneling patterns.)
Flooring
Wood floors in gyms, factories and homes take an incredible
beating. Douglas Fir's strength, beauty and old-fashioned toughness
are all prime reasons for choosing this long-lasting wood. Douglas
Fir provides a tough surface that will hold a finish, maintain its
appearance under extreme wear and remain level without cracking,
scuffing or splintering.
Douglas Fir flooring is available in 1x4 (nominal)
sizes in standard lengths 4 feet and longer. Flooring is machined
tongue-and-groove and may be finished in any grade. However, the
grade specifically developed for flooring is C & BTR FLOORING, which
can be sawn vertical grain for a more refined look.
Characteristics and grades
Douglas Fir has an enviable performance record. The
species has earned respect from industrial users worldwide because
when it comes to high performance demands and extreme stress conditions,
Douglas Fir meets the test. With its tough, strong fiber, high strength
in relation to its weight and dense grain structure, Douglas Fir
is a natural choice for industrial and remanufacturing uses.
Highly resistant to mechanical abrasion and chemical
reaction, Douglas Fir is often used in fabricating vats, tanks,
containers, flumes, conduits and similar industrial components that
call for an inert material with a long life under rigorous service
conditions. Truss fabrication and formwork, mining and tunneling,
trestles, bridges, railroad ties, stadiums, warehouses, storage
facilities and factories all utilize Douglas Fir lumber.
Industrial products include both structural and non-structural
grades that are intended for specific applications. Structural grades
are used for mining timbers, scaffold plank, foundation lumber and
stress-rated boards. Specialized non-structural grades include pickets,
lath, battens, stepping and even gutters (used primarily for historic
preservation projects). Factory and Shop lumber, one of the three
primary grading classifications of Western lumber products, is non-structural,
industrial lumber intended for remanufacturing into an enormous
array of products.
Factory and Shop lumber
Millwork standards require that the wood be easy
to machine, be of a consistent grade, have few visible knots, be
dimensionally stable and have a smooth surface texture. In addition,
the grain must be handsome in appearance, the wood easy to glue,
hold fasteners well and readily accept finishes. Three western softwood
species are consistently specified for millwork: Ponderosa Pine,
Douglas Fir and Hem-Fir (a species combination of Western Hemlock
and the True Firs). When hardness is desired, in addition to fine
appearance, Douglas Fir rivals many hardwoods.
Factory lumber is produced primarily for doors, windows,
furniture, frames, moulding and boxes. The grades are especially
well suited for ripping and cross cutting to obtain clear pieces
for remanufacturing. Factory grade criteria includes specifications,
within the grades, for the percentage of the lumber that is available
for cuttings in predetermined sizes and qualities, based on typical
U.S. joinery and millwork specifications. Moulding stock, which
comes in several thicknesses and widths, is suitable for ripping
into strips 1 inch and wider by 10 feet and longer.
Shop lumber, nominal 4/4 thickness to 16/4, is used
in remanufacturing for sashes and doors, jambs and door component
parts, boxes and specialty goods.
Factory and Shop lumber is usually shipped in large
quantities, mill-direct to remanufacturers. Many WWPA Member companies
can accommodate special remanufacturing requirements through buyer/seller
agreements.
(Refer to WWPA's Vol. 3 Species Book: Factory
Lumber for additional information and color photographs of the Factory
and Shop grades.)
Stress-rated boards
Stress-Rated Boards are available in Douglas Fir to
provide a range of products suitable for special applications where
applied design values are a requirement. Uses include light trusses,
belt rails, horizontal bracing, rafters and box beams for factory
built homes. When Stress-Rated Boards are gradestamped, the grade
name or number for the Dimension grade will be shown on the grade
stamp along with "SRB" to designate that a board product
may be used structurally.
Highways, bridges and railroads
Douglas Fir bridges -- either in the solid sawn designs
of past years or in today's glued, stress-laminated forms -- span
roads and rivers, lead hikers into the wilderness or over gorges
and offer access for everything from golf carts to semi-trailers
and heavy machinery. Douglas Fir is a top choice when the material
must resist slivering and indentation, be strong, durable, functional
and yet, at home in its natural surroundings.
While wooden bridges have been around for centuries,
today's engineered bridges of treated wood offer communities some
new advantages. They are strong, durable, cost-effective, time efficient
to install and reduce the impact of construction on surrounding
streamside ecology. Today's technology for stress-laminated wood
bridges is gaining wide acceptance throughout the U.S. and in other
countries.
Douglas Fir is also the species of choice for sound
barrier walls along freeways or for highway guard rails which demand
a wood that is treatable, paintable and strong with excellent fastening
capability.
Given its resilience under tremendous loads and vibration,
and the ability to take and hold heavy railroad spikes tightly,
it's clear why Douglas Fir still dominates the railway tracks. From
rail car linings and track supports to ties and cross-planking,
this Western species, treated and untreated, provides long-lasting
solutions to very tough jobs.
Douglas Fir preservative pressure-treated wood pilings
provide long-life performance with resistance to the corrosive salt
water conditions of wind, waves, storms and tides. When dramatic
design solutions are called for on hillsides or in hurricane country,
pressure-treated Douglas Fir pole construction is often the best
and most economical solution. Design loads as high as 70 tons have
been specified and ultimate loads as high as 235 tons have been
carried by Douglas Fir lumber. Treated DF products are also consistently
found in foundation stud and plywood walls, vehicular bridges, walkways,
parks shelters and foot bridges.
In pressure treating, preservatives are forced into
the wood cells and become permanently fixed (nonleaching). Because
of its cell structure, Douglas Fir requires incising (small slits
cut into the wood's surface before treatment) to improve chemical
penetration. Chemical retention is stated in terms of the weight
of the chemical retained per cubic foot (pcf) of wood after treatment;
the larger the number, the more chemical retained.
All pressure-treated wood should bear the quality
control mark of an agency approved by the American Lumber Standard
Committee. Look for the check mark ™ to indicate ALSC accreditation
of the quality mark, stamp or end tag.
For more information on treated lumber, contact the
Western Wood Preservers Institute.
Quality control
Lumber buyers may look to WWPA's registered grade
mark for the assurance that the lumber will consistently meet grade
specifications and performance standards.
The Association maintains a team of lumber inspectors
to monitor lumber grading and product quality control in its Member
mills and to provide mill inspection and grading performance reports,
lumber grader training and incentive programs, MSR and glued products
standards, resource recovery and mill efficiency studies.
In addition, WWPA provides technical and product support
services and information on Western lumber end uses for lumber buyers
throughout the world and publishes a variety of statistical reports
on Western lumber production, distribution and consumption.
To order a full-color version of this publication,
complete with photos and examples of grades, or any other WWPA title
referred in this text, go to the WWPA Online
Publications Store.
For a list of WWPA Member mills that produce Douglas Fir lumber
products, go to the WWPA Online Buyers' Guide.
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