Mature trees can grow 55m heigh and live for more than 1000 years. The bark of young trees is grey-green with highly scented blisters, and becomes purple-brown, thick and corky with horizontal fissures over time. The distinctive buds resemble those of beech trees - they are red-brown, scaly and slender, and taper to a point. The needle-like leaves are flat, soft and flexible, and distributed around the twig. They are green in colour with white-green stripes on the underside.
Douglas fir is monoecious, meaning both male and female flowers are found on the same tree. Male flowers are oval clusters of yellow stamens growing on the underside of the previous year's shoots. Female flowers are green to red upright tufts, and grow at the tips of twigs. After pollination by wind, female flowers develop into oval cones, which hang straight down from the branches and change in colour from yellow to pink to light brown. From each scale protrudes a unique three-pointed bract.
Interesting fact: Douglas fir bark is non-flammable. This protects the tree from fires in its native range.
Heart wood is light reddish brown when dry (although quite pink when fresh sawn) with contrasting creamy white sap. There is a strong contrast in colour between early and late growth which gives prominent growth rings resulting in strong grain pattern and figure. Uk trees seem less resinous than imported and are probably faster growing.
Douglas fir is good for structural work rated BS EN 350 class 3 moderately durability (see below), suitable from cladding, fencing, field shelters, stables, beams and support columns etc.
Kiln dried Douglas Fir is a very versatile timber. Good for most joinery or furniture work, also excellent air dried external cladding, it has a nice machined surface, it’s a mellow colour, not orangey.
Co2 Timber can supply a very good treatment for protection and maintaining the natural colour of Douglas fir. Please contact us for detail contact us.
Durability is the ability of a species to resist decay either naturally or through preservatives. The Class is based on the ability of the heartwood (inner part of the tree) to resist fungal decay. The sapwood (the living outermost portion of the tree)is considered not durable and should not be used for external projects without preservative.
BS EN 350 has 5 classes of durability they are:-
Class 1 to 3 can be left as untreated timber, a natural ageing process will accrue e.g. Cedar will turn a grey colour. Class 4 and 5 will need to be treated with preservatives.
For further information see www.greenspec.co.uk/building-design/cladding-durability-quality