Douglas Fir is quite durable and is frequently used for external cladding and in heavy construction such as house building.
Douglas Fir has a light reddish-brown colour with a close, uniformed grain.
Pseudotsuga menziesii, taxifolia, douglasii
Although a native of North America, the tree has been extensively planted in Europe and the UK.
The heartwood is light reddish-brown in colour, usually quite distinct from the lighter-coloured sapwood. The abrupt change and contrast in colour between early-wood and late-wood bands, produce a prominent growth ring figure which is a feature of plain-sawn surfaces and of rotary-cut veneer. The wood from trees grown in the UK appears to have rather less resin then the North American wood, and to some extent is of more rapid growth. The average weight of dried timber from either source is about 530 kg/m3.
Imported ‘Douglas fir’ is not a difficult timber to dry on arrival in this country of in Europe, because the moisture content has already been reduced prior to shipment with some selecting out of degraded boards. Drying degrade is generally confined to surface checking, split and loosening of knots , and splitting in the vicinity of knots. Accordingly, stock from trees grown in the UK and in Europe when dried from the green state, needs are, particularly because of the generally higher preponderence of knots which are hard, often loose, and which encourage more wavy grain than in imported stock.
Grade for grade, there is approximately the same strength properties in European or home-grown ‘Douglas fir’ and that imported from the mountain areas of North America. Compared with European redwood, it is some 60 per cent stiffer, 40 per cent harder and more resistant to suddenly applied loads, and 30 per cent stronger in bending and in compression along the grain.
‘Douglas fir’ grown in Europe and the UK on the whole is rather more difficult to work and machine than imported material due to the greater incidence of hard knots which can be troublesome especially when loosened, while fast grown stock can cause problems in sawing, drilling, mortising, and planning, due to tearing and splintering of the relatively soft early-wood. A characteristic feature of ‘Douglas fir’ is the abrupt transition between the early-wood and the dense late-wood, which appears to lift, and stand proud of the wood surface. Strictly speaking, it is the early-wood that becomes compressed, thus creating this effect, and in planning and moulding, dull cutters will cause this compression. A similar effect can also be created when absorbency of the early-wood can cause this to sink slightly and be held by the finishing media. Care must be therefore be taken in finishing, but good results can be obtained. It can be glued satisfactorily, and although tending to split, can be mailed and screwed.
Heavy construction, piling, house building, cats and tanks, laminating members, roof trusses, interior and exterior joinery, edge-grain flooring.
The above uses are applicable to imported stock in the sense that long experience has proved their suitability. Home grown or European stock is just as suitable by selection ; in some cases of an introduced timber species, the material may not be considered quite as good as its imported counterpart, but ‘Douglas fir@ is a tree that is tolerant of extreme variations in climatic conditions, and in its natural habitat will endure both the long, severe winters of North America, and the almost perpetual sunshine of the Mexican Cordilleras, producing excellent timber in either case. The tree has a pyramidal outline, with the lowest branches bending to the ground under open conditions and which would obviously tend to encourage knotty timber, but under controlled forestry conditions this should not eventually apply, bearing in mind that the full life of a ‘Douglas fir’ is many centuries, something like 700 years in fact, and the timber so far on the European market is relatively young, and fairly fast grown and often knotty.