Douglas Fir

Pseudotsuga menziesii

Products Graded for Structural Applications

Structural Products

When architects and engineers look for the best in structural timber, their first choice is often Douglas fir. It is universally recognized for its superior strength-to-weight ratio. It also provides excellent nail-holding and fastening capability that is documented with a superior performance record against wind, storms and earthquakes.

In strength properties, Douglas fir has the highest ratings of any western softwood for extreme fiber stress in bending; tension parallel-to-grain; horizontal sheer; compression perpendicular-to-grain and compression parallel-to-grain.

It also has the highest modulus of elasticity (E) values of all North American softwood species. E is the ratio of the amount a piece of timber will deflect in proportion to an applied load. This reflection of stiffness is one of the most important considerations in the design of floors and other horizontal systems. Douglas fir is often selected for four- and five-storey timber frame buildings.

Because of its physical working properties, as well as the moderate durability of its heartwood, and its excellent dimensional stability, all combine to provide the reasons why many builders worldwide prefer Douglas fir for framing timbers. It is truly the ideal, general-purpose softwood species for timber framing in residential, light commercial, multi-storey and industrial construction, and for structural formwork applications. Douglas fir products are also available preservative pressure treated for in-ground and ground-contact installations.

U.S. Dimension Timber:

Nominal sizes: 2" through 4" thick by 2" through 4" wide
(Surfaced Dry - 38 through 89 mm thick x 38 through 89 mm wide)
(Surfaced Green - 40 through 90 mm thick x 40 through 90 mm wide)

Structural Light Framing grades - for highest-strength engineered systems, trusses and multi-storey projects.
Light Framing grades - for routine framing in walls, plates, sills, cripples, blocking, etc.

Nominal sizes: 2" through 4" thick x 2" through 14" wide
(Surfaced Dry - 38 through 89 mm thick x 38 through 337 mm wide)
(Surfaced Green - 40 through 90 mm thick x 40 through 343 mm wide)

STUD grade: Intended for vertical-use applications, ideal for wall framing.

Nominal sizes: 2" to 4" thick by 5" and wider
(Surfaced Dry - 38 through 89 mm thick x 38 through 337 mm wide)
(Surfaced Green - 40 through 90 mm thick x 127 mm and wider)

Structural Joist and Plank grades - Intended to fit engineering applications such as floor and ceiling joists, roof rafters, headers, beams, trusses and general framing.

Special Dimension Timber

Machine Stress-Rated (MSR) timber - mechanically assessed for strength and connection capabilities, used for trusses and other engineered applications.

Structural-Glued timber – end- or finger-jointed; interchangeable with solid sawn dimension timber of the same grade and size; accepted for use under all U.S. Model Building Codes.

Structural Decking/Subflooring

Nominal sizes: 2" through 4" thick x 4" and wider
(Surfaced “DRY or MC 15” only- 38 through 89 mm thick x 89 mm and wider)
Primarily an industrial or commercial roof and flooring product. Also known as “roof decking.” Not intended for outdoor, backyard decks. Standard patterns, in 38 mm, 64 mm and 89 mm tongue-and-groove widths, available with “V” or rounded edges and other patterns to meet discriminating architectural requirements. Two grades available (WCLIB and WWPA Rules). Manufactured at 19% (S-DRY or KD) and 15% (MC15 or KD15) moisture content. Factory floors, manufactured from Douglas fir decking, result in a smooth, even surface; resist cracking and splintering under heavy, continuous use.

Large Sizes

Douglas fir is one of the few species available in large sizes from managed timberlands. While these products may be specified S-DRY, often they are shipped unseasoned, rough cut or surfaced on four sides (S4S). They are best known for their tough fiber, dense grain structure and strength. These “Heavy Timber” sections have the added benefit of excellent fire ratings that comply with U.S. and other countries’ Model Building Codes.

Beams & Stringers - nominal 5" and thicker (125 mm nominal) with a width more than 2" (50 mm nominal) greater than thickness.

Posts & Timbers - nominal 5" x 5" nominal (125 x 125 mm nominal) and larger with a width not more than 2" (50 mm nominal) greater than thickness.


Douglas fir is the ideal species for the most demanding wood-frame projects, particularly in areas where earthquakes and hurricanes are severe.
	High-performance Douglas fir products are well suited for multi-storey framing systems and engineered applications.
	A winner in the American Wood Design Awards 2000 competition, the simple frame of this barbecue facility at Champignon Garden in Tsukuba, Ibaraki, Japan, was constructed entirely of Douglas fir dimension lumber. Masayuki Akita + Quattro Architects & Planners.
	Structural decking grades are available for exposed applications (primarily ceilings) and for use as floors or sub-floors.
	Douglas fir offers a high degree of stiffness that is particularly desirable in floor and roof systems. The higher grades perform competitively with engineered products, but are much more economical.
Structural Light Framing grades include SELECT STRUCTURAL, NO.1 & BTR, NO.1, NO.2, and NO.3. Light Framing grades include CONSTRUCTION, STANDARD, and UTILITY. Stud grade applies only to STUDS. Structural Joists and Planks include SELECT STRUCTURAL, NO.1 & BTR, NO.1, NO.2, and NO.3. DF is the strongest of the western softwoods and marketed S-GRN, S-DRY and KD for framing applications.

Figure 1: SELECT STRUCTURAL is the highest Structural Light Framing grade —- sound, firm, encased and pith knots are limited to 22 mm, tight and well spaced.

Figure 2: STUD grade, suitable for all load-bearing walls; places limitations on crook, wane and edge knots.