All information provided by the Western Wood Products Association

www.wwpa.org

tree    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 Douglas tree; 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.

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.

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 grade stamping 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 grade stamped 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 grade stamped 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.

 

Moisture content and seasoning

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

Grade StampsThe 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 grade stamped with the following information:

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 grade stamped 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.
 

Products graded for structural applications

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.