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Douglas fir

Scientific name

Pseudotsuga menziesii. Family: Pinaceae

Other names

Oregon; oregon pine

Description

In natural stands in North America:

  • grows 40–60m high
  • reaches 1–2m diameter
  • 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.

Occurrence

  • Occurs naturally on the west coast of the USA and Canada.
  • A plantation species in other countries, particularly New Zealand.
  • Sawn timber is readily available.

Appearance

Colour

  • Heartwood ranges from yellowish through orange to deep red.
  • Sapwood is sometimes distinctly paler.

Grain

  • Generally straight.
  • Obvious difference in colour between earlywood and latewood results in a very distinctive figure (pattern) when back-sawn.

Other

  • Sapwood varies from 50mm wide in mature trees to 75mm in faster-grown plantation stems.

Uses

  • Engineering: sawn timber in heavy building construction (must be protected from the weather).
  • Construction: sawn timber in general house framing, flooring, lining, fascias, bargeboards and pergolas; not suitable for use in contact with the ground or for above-ground, weather exposed structures.
  • Decorative: furniture, plywood, joinery, turnery, carving.
  • Others: boat building (light), boat oars, scaffold planks, timber vats.

Properties

  • Density:
    • North America: 560kg/m3 at 12% moisture content; about 1.8m3 of seasoned sawn timber per tonne
    • New Zealand: 480kg/m3; about 2.1m3/tonne.
  • Strength groups:
    • North America: S5 unseasoned, SD5 seasoned
    • New Zealand: S6 unseasoned, SD6 seasoned.
  • Stress grades when visually stress graded in accordance with AS 2858—2001: Timber—Softwood—Visually stress-graded for structural purposes:
    • 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).
  • 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 impregnating with commercial preservatives.
  • Seasoning: satisfactorily dries using conventional air and kiln seasoning.
  • Hardness: firm (rated 4 on a 6-class scale) to indent and work with hand tools.
  • Machining: machines, and turns well, but keep planer blades sharp to avoid surface ridging.
  • Fixing: nails may follow the growth rings; be careful using standard fastenings and fittings.
  • Gluing: satisfactorily bonds using standard procedures.
  • Finishing: some material has high resin content and earlywood/latewood ridging of dressed timber—carefully select timber for finishing and preparing surfaces for paint and varnish.

Identification features

General characteristics

  • Sapwood: usually paler than heartwood but sometimes indistinguishable.
  • 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 is very abrupt; latewood ranges 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 (soft tissue): none visible.
  • Rays: fine, not visible without a lens

Other features

  • Odour: distinctive odour.

Research and resources

  • Ilic, J 1991, CSIRO atlas of hardwoods, Crawford House Press, Bathurst, Australia.
  • Queensland Government, DAF 2018, Construction timbers in Queensland: Properties and specifications for satisfactory performance of construction timbers in Queensland. Class 1 and Class 10 buildings, Books 1 & 2, Department of Agriculture and Fisheries, Brisbane.
  • Standards Australia, 2008, AS 2858—2000: Timber—Softwood—Visually stress-graded for structural purposes, Standards Australia International, Strathfield, NSW.