Sitka spruce

Category: Softwood
Region: Coast
Title: Sitka spruce (Picea sitchensis)

With a high strength-to-weight ratio, Sitka spruce is used in a variety of structural products and is a favoured wood in the aircraft and shipbuilding industries. The top-grade clear wood is used for piano and guitar soundboards as it has excellent resonating properties.

Sitka spruce is the largest of the spruces, growing up to 70 metres tall and two metres in diameter. Found along the Pacific Coast, it is valued for wood that is light, soft, relatively strong and flexible.

Where it grows

Sitka spruce grows in a narrow band along BC’s coast from sea level to about 700 metres. It is rarely more than 80 kilometres inland and is most common along the coastal fog belt and on river and stream floodplains.

The species grows in pure stands, but is also commonly mixed with Douglas-fir, western red cedar and red alder. Pure stands may develop on the Pacific Coast where ocean spray has a strong influence on vegetation because Sitka spruce tolerates sodium inputs where other trees may not.

Did you know?

With its high strength-to-weight ratio, Sitka spruce is a favoured wood in the aircraft and shipbuilding industries. The original flying plane built by the Wright Brothers and British Second World War Mosquito bombers were made with Sitka spruce.

Identifiable characteristics

Sitka spruce is a large tree that grows to a height of 70 metres and a diameter of two metres when mature with an estimated lifespan of 700 to 800 years. The largest known Sitka spruce in BC is 95 metres tall and five metres across. The bark is very thin, brown or purplish-grey, and breaks up into small scales.

Sitka spruce needles are light green to bluish-green, stuff and sharp. They are four-sided but slightly flattened with two white bands running along the upper surface and two narrower bands along the lower surface. The needles are arranged spirally along the twig and are attached by small pegs that remain on the twig after the needles fall.

Seed cones are reddish to yellowish brown and hang from the crown. Their seed scales are thin, wavy, and irregularly toothed. Pollen cones are red.

Did you know?

Carmanah Walbran Provincial Park on western Vancouver Island offers protection to diverse forest ecosystems and is home to some of the world’s largest Sitka spruce trees—including one that is 95 metres tall and more than 800 years old.

Common uses and applications

Sitka spruce is used to make a variety of structural products. Because it is stronger than the same weight component made of steel, Sitka spruce is used to build airplane framework components. It has virtually no odour or taste so is suitable for food storage and processing.

High grades are popular for specialty marine applications such as masts, spars and deck beams, and for ladder stock and industrial equipment where a high strength-to-weight ratio is desired. The wood has excellent acoustic properties and is used to make sounding boards in pianos and other musical instruments such as violins and guitars. Clear grades are used in fine interior finishing such as sliding screens, mouldings, joinery and trim. It is particularly popular when an even-coloured natural wood finish is desired.

Indigenous peoples use Sitka spruce in winter dance ceremonies and for medicinal purposes. The inner bark is a good source of vitamin C and can also work as a laxative, and the pitch can be eaten or applied as a salve to burns, boils and other skin ailments. Indigenous peoples use softened pitch to waterproof boats and fishing gear, and they use the roots to create beautiful, water-tight hats, baskets, ropes, twine and fishing lines.

Did you know?

Sitka spruce was introduced into Europe in the 19th century and is now an important timber species in many countries, including Britain, Ireland, Norway, France and Denmark.

Commercial properties

Sitka spruce has a high strength-to-weight ratio and is well known for its working properties. The wood dries rapidly with small dimensional movement and little tendency to check. It is relatively easy to work, with good machining qualities. It planes and shapes well and can be sanded to a smooth finish. The wood glues easily, has a moderate nail and screw holding ability, and takes a good finish.

Commercial availability

In North America, structural grades are in accordance with the National Lumber Grades Authority (NLGA) rules for dimension lumber. Sitka spruce is currently marketed under the Northern Species group, one of four species combination groups of Canadian lumber. Its official structural design value is lower than the other three: SPF (spruce-pine-fir), Hem-Fir and Douglas Fir-Larch.

Sitka spruce is commonly produced in appearance grades according to NLGA rules. Clears, shop lumber and moulding stock are most common. Sitka spruce is also offered in export grades for Japan and other markets.

Sitka spruce 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.

Sitka spruce – physical properties

Density (kg/m3)Green347
Air dry387
Specific gravity (12% m.c.)Standard0.35
Hardness (N)Side2200
End3090
MOE (Mpa)Green9450
Air dry11200
MOR (Mpa)Green37.4
Air dry69.8
Compression parallel (Mpa)Air dry37.4
Compression perpendicular (Mpa)Air dry4.10
Shear (Mpa)Air dry6.78
Cleavage (N/mm width)Air dry38.0
ShrinkageRadial (OD)4.6%
OD = oven dryTangential (OD)7.8%
air = air dry 12%Volumetric (OD)11.7%
Volumetric (air)6.0%
Tang / rad ratio1.7

Sitka spruce – visual properties

Colour
HeartwoodLight pinkish-brown.
SapwoodCreamy white to light yellow.
Heartwood / sapwood contrastThe sapwood is wide with little contrast between heartwood and sapwood.
Latewood / earlywood contrastThe annual growth rings have a gradual transition from earlywood to latewood.
Grain
The wood is generally straight-grained with a fine, uniform texture.
Figure
Plainsawn lumber or rotary-cut veneer: distinct, inconspicuous growth ring.
Quartersawn lumber or quarter-sliced veneer: faint growth ring stripe.
Other
Non resinous, without odour.

Sitka spruce – working properties

ProcessPerformanceComments
Machining
PlaningExcellent planing qualityRecommended planer settings: 12° hook angle and 20 kmpi (knife marks per inch). Takes a smooth silky finish provided sharp tools are used.
TurningMedium to low surface qualityCommon defects: torn out grain.
SawingEasy to work with toolsEasy to work provided cutting edges are kept sharp and the wood is free of knots.
BoringMediumMedium boring quality with brad point bits and poor quality with single twist bits.
MortisingGoodGood mortising quality when using both chain and hollow chisel mortises.
ShapingGood shaping qualityRecommended: the use of a counter piece for end-grain shaping.
VeneeringGood
SandingGoodExcellent sanding quality.
Fastening
ScrewingModerateAverage screw rentention: 402 lb.
Nail retention Good
Lateral nail holdingN/A
GluingEasy Bonds very easily with adhesives of a wide range of properties and under a wide range of bonding conditions.
Finishing
StainingEasy to moderateSmooth finish achieved. Light stains work well but dark stains magnify the uneven colours produced by different textures in wood. A wash coat would even out the colour.
PaintingAverage to good paint holding ability
LacqueringGood
WaxingGoodBest results are obtained when using light-coloured waxes (e.g. mellow pine).
Drying
Ease of dryingEasy to moderately easyDries rapidly and quite well, but care is required to reduce warping, splitting and loosening of knots.
Durability
Natural decay resistanceSlightly durableNot appropriate for prolonged outdoor exposure.
TreatabilityImpermeableCan be improved by incising.