Wood species
Sitka spruce wood
Sitka spruce is a softwood (Picea sitchensis). At 12% moisture content it has a Janka hardness of 510 lbf (2,269 N) and it weighs about 28 lb/ft³ (448 kg/m³), 2.3 lb (1.06 kg) per board foot.
Also called: tideland spruce, silver spruce.
Key numbers
- Janka hardness, 12% MC
- 510 lbf (2,269 N)
- Green: 350 lbf (1,557 N)
- Weight at 12% MC
- 28 lb/ft³ (448 kg/m³)
- 2.3 lb per board foot
- Specific gravity (oven-dry weight)
- 0.40 at 12% MC volume
- 0.37 on green volume
- Shrinkage, green to oven-dry
- 7.5% tangential
- Radial 4.3%, volumetric 11.5%
One source: USDA Forest Products Laboratory, the authority for species properties it measured
Why: Measured by the USDA Forest Products Laboratory; Sitka spruce's density is worked from its specific gravity with the Handbook's own equation.
How much Sitka spruce moves
A 12 in wide flatsawn board of Sitka spruce that goes from 6% to 12% moisture content swells about 0.19 in (about 3/16 in, 4.8 mm). Quartersawn, the same board moves about 0.11 in (about 3/32 in, 2.7 mm). Flatsawn faces move 1.7 times as much as quartersawn ones, because the wood shrinks 7.5% around the growth rings but only 4.3% across them.
Worked with the Wood Handbook's dimensional change coefficients for Sitka spruce (Table 13-5: 0.00263 tangential, 0.00148 radial per 1% change in moisture content), which hold between 6% and 14%. Individual boards vary: the Handbook gives shrinkage a coefficient of variation of about 15% (p. 4-11).
Color, grain and working
- Color
- Light pinkish-brown heartwood shading into wide, creamy white sapwood.
- Grain and texture
- Comparatively fine and uniform, generally straight, with no distinct taste or smell; available in long, clear pieces.
- Working and character
- Moderately light, soft and fairly weak in absolute terms, but high in strength for its weight, with fairly low shrinkage.
- Uses
- Piano sounding boards, ladder rails, boats, furniture and millwork; historically the most important aircraft wood.
Adapted in our own words from the Wood Handbook, Chapter 2, p. 2-18.
Strength
Bending strength is the modulus of rupture (MOR); stiffness is the modulus of elasticity (MOE). Clear, straight-grained samples of Sitka spruce tested by the Forest Products Laboratory (Wood Handbook Table 5-3b). Knots and cross grain make lumber weaker than these clear samples (Handbook Chapter 5).
| Property | Green | 12% MC |
|---|---|---|
| Bending strength (MOR) | 5,700 psi (39 MPa) | 10,200 psi (70 MPa) |
| Stiffness (MOE) | 1,230,000 psi (8.5 GPa) | 1,570,000 psi (10.8 GPa) |
| Crushing strength (compression parallel to grain) | 2,670 psi (18 MPa) | 5,610 psi (39 MPa) |
| Compression perpendicular to grain | 280 psi (2 MPa) | 580 psi (4 MPa) |
| Shear parallel to grain | 760 psi (5 MPa) | 1,150 psi (8 MPa) |
| Tension perpendicular to grain | 250 psi (2 MPa) | 370 psi (3 MPa) |
A dash means the Handbook prints no value; none is filled in.
Dust and health
- Wood dust is classed as carcinogenic to humans (Group 1) by the International Agency for Research on Cancer, chiefly for cancers of the nose and sinuses.
- NIOSH recommends keeping wood dust exposure to 1 mg/m³ of total dust, as quoted in OSHA's sawmill guidance.
This is what the named authorities publish, not medical advice.
Compare with
Why these numbers
Why these numbers?
The situation
The USDA Forest Products Laboratory measured Sitka spruce at 510 lbf of side hardness at 12% moisture content, on clear, straight-grained samples (Wood Handbook Table 5-3b).
One source: USDA Forest Products Laboratory, the authority for species properties it measured , sources [1]
What that means
Side hardness (Janka) is the load needed to press a 0.444 in (11.28 mm) steel ball halfway into the wood across the grain; a higher number dents less (Handbook p. 5-5).
One source: USDA Forest Products Laboratory, the authority for species properties it measured , sources [1]
So
Density at 12% is water's density × specific gravity × (1 + 0.12) (Handbook Eq. 4-14): 62.43 × 0.40 × 1.12.
Arithmetic: exact by definition , sources [1]
The number
About 28 lb/ft³, or 2.3 lb per board foot (1/12 ft³), at 12% moisture content.
Arithmetic: exact by definition
Sources