Douglas Fir
Douglas fir (Pseudotsuga menziesii) is one of the best known wood species in the world. In British Columbia there are two varieties of Douglas-fir, Coastal and Interior. The Coastal variety occurs along the southern mainland Coast and across Vancouver Island, except for the very northern tip. The Interior variety is found throughout southern British Columbia, and as far north as the centre of the province. Douglas-fir is a large tree reaching heights of 85 metres on the Coast, and 42 metres in the Interior. Douglas-fir makes up 8.8% of the provincial growing stock.
Common Uses
Douglas-fir is primarily used for building and construction purposes due to its strength advantages and availability of large dimensions from old-growth trees. It is one of the finest timbers for heavy structural purposes, including laminated arches and roof trusses. Structurally, it is used in the form of lumber, timbers, pilings and plywood.
Douglas-fir is seen as a first class wood for the manufacturing of sashes, doors and windows. The wood is also used to produce a wide variety of products including general millwork, flooring, furniture, cabinets, veneer, vats, ship and boat construction, transmission poles, and marine pilings.
What is the difference between Coastal and Interior Douglas-fir?
Coastal Douglas-fir is a much bigger tree than Interior Douglas-fir. The timber from the Coastal trees is generally lighter in colour, and more uniform in texture than that of Interior trees. Both have the same wood properties, however, one main difference is that Interior Douglas-fir is less permeable to preservative treatments.
Douglas-fir lumber is dried according to end-use and customer specifications. Kiln drying inhibits natural staining of the wood, improves its strength and stiffness, enhances its appearance, and increases its resistance to decay and attack by insects.
| Physical Properties |
|---|
| Density (kg/m3) | Green | 450 |
| Air Dry | 487 |
| Specific Gravity (12% M.C.) | Standard | 0.45 |
| Hardness (N) | Side | 2990 |
| End | 4020 |
| MOE (Mpa) | Green | 11100 |
| Air Dry | 13500 |
| MOR (Mpa) | Green | 52.0 |
| Air Dry | 88.6 |
| Compression Parallel (Mpa) | Air Dry | 50.1 |
| compression Perpendicular (Mpa) | Air Dry | 6.01 |
| Shear (Mpa) | Air Dry | 9.53 |
| Cleavage (N/mm Width) | Air Dry | 38.9 |
Shrinkage
OD=oven dry
air=air dry 12% | Radial (OD) | 4.8% |
| Tangential (OD) | 7.4% |
| Volumetric (OD) | 11.9% |
| Volumetric (air) | 7.0% |
| Tang / Rad ratio | 1.5 |
Working Properties
Douglas-fir has excellent strength properties and is well known for its workability. The wood dries rapidly with small dimensional movement and little tendency to check. It is relatively easy to work, with good machining qualities. It turns, planes and shapes well and can be sanded to a smooth finish. The wood glues moderately easily, has moderate nail and good screw holding ability, and takes a good finish.
| Process | Performance | Comments |
|---|
| Machining |
|---|
| Planing | Good planing quality | Good surface quality. Typical defects are raised grain and fuzzy grain. |
| Turning | High surface quality | Very good surface quality. |
| Sawing | Easy to work with tools | Easy to work with both hand and power tools. Moderate to severe blunting effect. Resin build up on cutters may cause problems. |
| Boring | Good | Very good boring quality. |
| Mortising | Excellent | Excellent mortising quality with both chain mortise and hollow chisel mortise. |
| Shaping | Excellent shaping quality | |
| Veneering | Excellent | Important plywood species. |
| Sanding | Good | Very good sanding properties. |
| Fastening |
|---|
| Screwing | Good | Very good holding. Excellent resistance to splitting. A verage screw retention: 494 lb. |
| Lateral Nail Holding | Good | Good holding. Excellent resistance to splitting. |
| Nail Retention | Good | |
| Gluing | Glues to moderate | Bonds well with a fairly wide range of adhesives under a moderately wide range of bonding conditions. |
| Finishing |
|---|
| Staining | Easy | Old-growth: Smooth finish. Grain becomes wild and pronounced with dark stain. A clear coating works the best. Second-growth: Stainability is average for light colours, poor for dark ones. Good results with light stain or clear finish followed by nitrocellulose alkyd clear sealer and finish. Rotary cut veneers are reported to display such strong natural color that staining is sometimes unnecessary. |
| Painting | Average to good paint holding ability | Satisfactory to good results. |
| Lacquering | Excellent results | |
| Waxing | Good | Very good results are obtained when using light- to medium-coloured waxes, such as Mellow Pine and Chestnut. |
| Drying |
|---|
| Ease of Drying | Easy to moderately easy | A relatively easy wood to dry with little trouble occurring from checking, warping and splitting. Lower grades require more care. |
| Durability |
|---|
| Natural Decay Resistance | Moderately durable | Should not be used in applications with prolonged ground contact without treatment. |
| Treatability | Impermeable to extremely impermeable | Can be improved by incising. |
Commercial Availability
Douglas-fir is marketed predominantly as Douglas-fir – Larch in structural grades according to National Lumber Grades Authority (NLGA) rules for dimension lumber. Select Structural, #2 and better and stud grades are the most common grades produced. Specialty in-house grades, and export grades are also available.
Appearance grades are also produced according to NLGA rules. Clears, shop lumber and moulding stock are most common, though there are many potential appearance grades that can be produced.
Sources
BC Wood Specialties Group, www.bcwood.com
Coast Forest Products Association, www.coastforest.org