What special features does the Douglas fir have as a material?
Abbreviation DIN EN 13556: PSMN
Botanical name: Pseudotsuga menziesii, family Pinaceae
Distribution: west coast of North America, in Europe, Chile and New Zealand cultivated trade names: Douglas fir, Douglas fir (D); Douglas fir, Oregon pine; Douglas vert (FR); douglasia (IT).
Oregon Pine, Red fir or Yellow fir, as Pseudotsuga menziesii is called in North America, is one of the most important tree species supplying sawn timber in its natural area of distribution. Very good growth characteristics in native locations made the Douglas fir, as it is called in Germany, also interesting for European forestry.
The first stands were planted in Germany at the end of the 19th century. Today, the Douglas fir accounts for approximately 1.7 % of Germany’s total forest area, or 179,607 hectares. Douglas firs cultivated outside their natural range are mostly characterized by a high proportion of juvenile wood with broad annual rings and a high proportion of branches, which significantly distinguishes the wood characteristics from fine-grained wood from North America.
Oregon pine is one of the tallest trees on earth, trunks from virgin forest stands usually 20 m knotless and 0.9 to 1.5 m thick, round and straight-edged.
Color and structure
The sapwood is white to yellowish-grey and, depending on the age of the tree, narrow to wide. It is thus distinguished from the core, which is light yellow-brown to reddish-brown in fresh condition and darkens considerably. The abrupt alternation of early and late wood within an annual ring results in pronounced grain on the tangential surfaces and contrasting stripes on the radial surfaces. Depending on age, native, young stands tend to form broad annual rings (5 to 10 mm). Fine-grained qualities (1 to 3 mm) are imported from North America. The small scattered resin channels are hardly visible in fine-grained material and contain a very volatile resin. This gives fresh wood in particular a pungent aromatic and unique smell.
Straight grained structured wood, sometimes very decorative, but rich in knots.
European qualities, with a high proportion of juvenile wood and knots, do not yet correspond to the qualities of imported wood.
The workability of Douglas fir is essentially dependent on the width of the annual rings. Narrow-ringed wood can be worked very well. Wider growth rings and knots increase the inhomogeneity of the fabric and thus the risk of splitting, chipping or fibre tearing during nailing, screwing or planing and profiling. Fine qualities are easy to cut. After removal of any resin residues, bonding is just as good as surface treatment is problem-free. The impregnability of the heartwood, however, is poor. Contact with iron ions triggers pronounced grey-black discolouration reactions in Douglas fir.
Douglas fir can be dried technically well and quickly. Mild drying and subsequent storage for as long as possible are recommended to avoid intensive resin leaks.
Natural durability (DIN-EN 350-2)
The natural durability according to DIN EN 350 is classified in class 3-4 for European wood and in class 3 for wood from North America without restrictions, depending on the origin.
Areas of application
The Douglas fir is suitable for outdoor use without ground contact as well as for decorative use indoors. The wood is mainly used in gardening and landscaping, for children’s playgrounds, exterior cladding (facades) and in the USA as weatherproof glued building plywood, as well as for frame construction, floors and stairs. Fine qualities are in demand for sailing boat masts and decorative veneers.
Due to similar trade names of some firs (Fir from the USA), confusion may occur between the different ranges. Contained terpenes, are allergenic.
Douglas fir – Technical properties
Weight fresh640 – 800 kg/m³
Bulk density air-dry (12-15% u)0.35 – 0.51 – 0.77 g/cm³
Compressive strength u12-1542 – 68 N/mm²
Flexural strength u12-1570 – 100 N/mm²
Modulus of elasticity (bending) u12-1511 000 – 13 200 N/mm²
Hardness (JANKA) ⊥, converted3.1 – 7.3 kN
Hardness (BRINELL) ⊥ to fiber u12-1517 – 30 N/mm²
Differential shrinkage (radial)0.15 – 0.19 %
Differential shrinkage (tangential)0.24 – 0.39 %pH-Wert≈ 3.66
Natural durability (DIN-EN 350-2)Class 3 – 4(Eu), 3(nAm)