Douglas fir

Scientific name

Pseudotsuga menziesii. Family: Pinaceae

Local names

Oregon, Oregon pine

Description and natural occurrence

In natural stands in North America it attains a height of 40 to 60 m and can reach 1 to 2 m in diameter. In such forests, the trunk is clear of branches for about two thirds of its height and therefore produces a high percentage of clear wood. Bark is very fibrous.

Douglas fir occurs naturally on the west coast of the USA and Canada. It is also a plantation species in other countries, particularly New Zealand.

Sawn timber from this species is readily available.

Wood appearance

Colour. The heartwood ranges from yellowish through orange to deep red. Sometimes the sapwood is distinctly paler, varying in width from 50 mm in mature trees to 75 mm in faster grown plantation stems.

Grain. Generally straight. A pronounced difference in colour between earlywood and latewood results in a very distinctive figure when backsawn.

Wood properties

Density. North America: 560 kg/m3 at 12% moisture content; approximately 1.8 m3 of seasoned sawn timber per tonne. New Zealand: 480 kg/m3; approximately 2.1 m3 /tonne.

Strength groups. North America: S5 unseasoned; SD5 seasoned; from New Zealand S6 unseasoned; SD6 seasoned.

Stress grades. North America: F4, F5, F7, F8, F11 (unseasoned), F7, F8, F11, F14, F17 (seasoned). New Zealand F4, F5, F7, F8 (unseasoned), F5, F7, F8, F11, F14 (seasoned), when visually stress graded in accordance with AS 2858-2001, Timber - softwood - visually stress-graded for structural purposes.

Shrinkage to 12% MC. 5.0% (tangential); 3.0% (radial).

Unit shrinkage. 0.38% (tangential); 0.23% (radial).

Durability above-ground. Class 4 - life expectancy less than 7 years.

Durability in-ground. Class 4 - life expectancy less than 5 years.

Lyctine susceptibility. Sapwood not susceptible to lyctine borer attack.

Termite resistance. Not resistant.

Joint groups. North America: J4 unseasoned; JD4 seasoned. New Zealand: J5 unseasoned; JD4 seasoned.

Preservation. Sapwood and heartwood are both very resistant to commercial preservative impregnation.

Seasoning. Can be satisfactorily dried using conventional air and kiln seasoning methods.

Hardness. Firm (rated 4 on a 6 class scale) in relation to indentation and ease of working with hand tools.

Machining. Machines and turns well but planer blades should be kept sharp to avoid surface ridging.

Fixing. Nails may tend to follow the growth rings. Care is therefore needed with the use of standard fastenings and fittings.

Gluing. Can be satisfactorily bonded using standard procedures.

Finishing. High resin content of some material and earlywood/latewood ridging of dressed timber mean that care is required in selecting timber for finishing applications and in preparation of surfaces for paint and varnish finishes.

Uses

Engineering. As sawn timber in heavy building construction (must be protected from the weather).

Construction. As sawn timber in general house framing, flooring, lining, fascias, bargeboards and pergolas. It is not suitable for ground contact uses or for above-ground, weather exposed structural uses.

Decorative. Furniture, plywood, joinery, turnery, carving.

Others. Boat building (light), boat oars, scaffold planks, timber vats.

Identification features

General characteristics

Sapwood. Sometimes indistinguishable from heartwood, but usually paler in colour.

Heartwood. Variable; yellowish to orange red or deep red.

Texture. Fine with prominent growth rings; grain normally straight except where knots are present.

Wood structure

Growth rings. Very distinct; transition from earlywood to latewood very abrupt. Latewood ranging from very narrow to very wide.

Resin canals. Uncommon but occurring both in longitudinal and radial directions and visible only with a lens.

Vessels. Absent.

Parenchyma. None visible.

Rays. Fine, not visible without a lens.

Other features

Odour. Douglas fir has a distinctive odour.

Further reading

Hopewell, G (ed.) 2006, 'Construction timbers in Queensland: properties and specifications for satisfactory performance of construction timbers in Queensland, Class 1 and Class 10 buildings', books 1 and 2, Department of Primary Industries and Fisheries, Brisbane.

Ilic, J 1991, 'CSIRO atlas of hardwoods', Crawford House Press, Bathurst, Australia.

Standards Australia, 2000, 'AS 2082-2000: Timber - hardwood - visually stress-graded for structural purposes', Standards Australia.

Last updated 04 August 2010