Wood species
Western larch wood
Western larch is a softwood (Larix occidentalis). At 12% moisture content it has a Janka hardness of 830 lbf (3,692 N) and it weighs about 36 lb/ft³ (582 kg/m³), 3 lb (1.37 kg) per board foot.
Also called: larch.
Key numbers
- Janka hardness, 12% MC
- 830 lbf (3,692 N)
- Green: 510 lbf (2,269 N)
- Weight at 12% MC
- 36 lb/ft³ (582 kg/m³)
- 3 lb per board foot
- Specific gravity (oven-dry weight)
- 0.52 at 12% MC volume
- 0.48 on green volume
- Shrinkage, green to oven-dry
- 9.1% tangential
- Radial 4.5%, volumetric 14.0%
One source: USDA Forest Products Laboratory, the authority for species properties it measured
Why: Measured by the USDA Forest Products Laboratory; western larch's density is worked from its specific gravity with the Handbook's own equation.
How much western larch moves
A 12 in wide flatsawn board of western larch that goes from 6% to 12% moisture content swells about 0.23 in (about 7/32 in, 5.9 mm). Quartersawn, the same board moves about 0.11 in (about 1/8 in, 2.8 mm). Flatsawn faces move 2 times as much as quartersawn ones, because the wood shrinks 9.1% around the growth rings but only 4.5% across them.
Worked with the Wood Handbook's dimensional change coefficients for western larch (Table 13-5: 0.00323 tangential, 0.00155 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
- Yellowish-brown heartwood and narrow yellowish-white sapwood.
- Grain and texture
- Usually straight; it splits easily and is prone to ring shake. Knots are common but small and tight.
- Working and character
- Stiff, moderately strong, hard and heavy, with fairly high shrinkage. Close to Douglas-fir, and sometimes sold mixed with it.
- Uses
- Rough dimension lumber, small timbers, planks, poles and posts; high grades for flooring, interior woodwork, sashes and doors.
Adapted in our own words from the Wood Handbook, Chapter 2, p. 2-13.
Strength
Bending strength is the modulus of rupture (MOR); stiffness is the modulus of elasticity (MOE). Clear, straight-grained samples of western larch 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) | 7,700 psi (53 MPa) | 13,000 psi (90 MPa) |
| Stiffness (MOE) | 1,460,000 psi (10.1 GPa) | 1,870,000 psi (12.9 GPa) |
| Crushing strength (compression parallel to grain) | 3,760 psi (26 MPa) | 7,620 psi (53 MPa) |
| Compression perpendicular to grain | 400 psi (3 MPa) | 930 psi (6 MPa) |
| Shear parallel to grain | 870 psi (6 MPa) | 1,360 psi (9 MPa) |
| Tension perpendicular to grain | 330 psi (2 MPa) | 430 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 western larch at 830 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 × 0.52 × 1.12.
Arithmetic: exact by definition , sources [1]
The number
About 36 lb/ft³, or 3 lb per board foot (1/12 ft³), at 12% moisture content.
Arithmetic: exact by definition
Sources