Wood species
Redwood wood
Redwood is a softwood; this page covers the redwood (old growth and young growth), led by old-growth redwood (Sequoia sempervirens). At 12% moisture content it has a Janka hardness of 480 lbf (2,135 N) and it weighs about 28 lb/ft³ (448 kg/m³), 2.3 lb (1.06 kg) per board foot.
Names and species on this page: coast redwood, California redwood, sequoia.
Key numbers
- Janka hardness, 12% MC
- 480 lbf (2,135 N)
- Green: 410 lbf (1,824 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
- 0.38 on green volume
- Shrinkage, green to oven-dry
- 4.4% tangential
- Radial 2.6%, volumetric 6.8%
One source: USDA Forest Products Laboratory, the authority for species properties it measured
Why: Measured by the USDA Forest Products Laboratory; redwood's density is worked from its specific gravity with the Handbook's own equation.
How much redwood moves
A 12 in wide flatsawn board of old-growth redwood that goes from 6% to 12% moisture content swells about 0.15 in (about 5/32 in, 3.7 mm). Quartersawn, the same board moves about 0.09 in (about 3/32 in, 2.2 mm). Flatsawn faces move 1.7 times as much as quartersawn ones, because the wood shrinks 4.4% around the growth rings but only 2.6% across them.
Worked with the Wood Handbook's dimensional change coefficients for old-growth redwood (Table 13-5: 0.00205 tangential, 0.0012 radial per 1% change in moisture content), which hold between 6% and 14%. For this species the Handbook assumes shrinkage starts at 22% moisture content instead of 30%. Individual boards vary: the Handbook gives shrinkage a coefficient of variation of about 15% (p. 4-11).
Color, grain and working
- Color
- Light “cherry” red to dark mahogany heartwood; narrow, almost white sapwood.
- Grain and texture
- Generally straight; it splits readily.
- Working and character
- Old growth is moderately light, strong, stiff and hard, easy to work, and shrinks and swells comparatively little. Old-growth heartwood is highly decay resistant; second-growth heartwood is usually only low to moderately so.
- Uses
- Siding, decking, outdoor furniture, tanks, millwork, fence material and decorative plywood.
The Handbook reports that the IUCN lists redwood as endangered because of extensive logging.
Adapted in our own words from the Wood Handbook, Chapter 2, p. 2-17.
Strength
Bending strength is the modulus of rupture (MOR); stiffness is the modulus of elasticity (MOE). Clear, straight-grained samples of old-growth redwood 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) | 7,500 psi (52 MPa) | 10,000 psi (69 MPa) |
| Stiffness (MOE) | 1,180,000 psi (8.1 GPa) | 1,340,000 psi (9.2 GPa) |
| Crushing strength (compression parallel to grain) | 4,200 psi (29 MPa) | 6,150 psi (42 MPa) |
| Compression perpendicular to grain | 420 psi (3 MPa) | 700 psi (5 MPa) |
| Shear parallel to grain | 800 psi (6 MPa) | 940 psi (6 MPa) |
| Tension perpendicular to grain | 260 psi (2 MPa) | 240 psi (2 MPa) |
A dash means the Handbook prints no value; none is filled in.
The redwood (old growth and young growth)
The Handbook tests each species separately; they are sold together as redwood. Across the 2 species measured, Janka hardness at 12% runs from 420 to 480 lbf.
| Species | Janka, 12% MC | Weight, 12% MC | Tangential shrinkage |
|---|---|---|---|
| Old-growth redwoodSequoia sempervirens | 480 lbf | 28 lb/ft³ | 4.4% |
| Young-growth redwoodSequoia sempervirens | 420 lbf | 24 lb/ft³ | 4.9% |
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 old-growth redwood at 480 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