Species

Species carry the physical properties that solid-lumber families inherit. Naming one in a material is what gives the validator something to reason with: a pine cleat and a maple rail of identical size take the same screw and hold it differently, and the report says so.

materials:
  - id: rail_stock
    from: lumber.hardwood.s4s
    species: walnut
    thickness: 38
    width: 190

Hardwoods

Available in lumber.hardwood.s4s and lumber.hardwood.rough.

Id		Density	E	MOR	Movement T / R	Screw face / end	Hardness
walnut	American black walnut	610	11 600	101	2.57 / 1.82	high / low	4490
white_oak	White oak	755	12 300	105	3.50 / 1.80	high / low	6000
red_oak	Red oak	700	12 500	99	3.47 / 1.37	high / low	5700
ash	White ash	670	12 000	103	2.60 / 1.60	high / low	5870
maple	Hard maple	705	12 600	109	3.23 / 1.60	high / low	6450
cherry	Black cherry	560	10 300	85	2.53 / 1.17	medium / low	4230
beech	European beech	720	14 300	103	3.87 / 1.87	high / low	5800
birch	Yellow birch	670	13 900	114	3.00 / 2.43	high / low	5580
poplar	Yellow poplar	455	10 900	70	2.73 / 1.40	medium / poor	2420

Softwoods

Available in lumber.softwood.s4s.

Id		Density	E	MOR	Movement T / R	Screw face / end	Hardness
pine	Scots pine / European redwood	510	10 100	83	2.47 / 1.33	medium / poor	2420
spruce	European spruce / whitewood	450	10 200	70	2.57 / 1.27	low / poor	1800
douglas_fir	Douglas fir	530	13 400	85	2.43 / 1.60	medium / poor	2900
western_red_cedar	Western red cedar	350	7700	51	1.67 / 0.80	low / poor	1560
larch	European larch	590	12 500	92	2.50 / 1.43	medium / poor	3200

Units: density kg/m³ · E (modulus of elasticity) MPa · MOR (modulus of rupture) MPa · movement % per 10% change in moisture content, tangential / radial · hardness N (Janka).

What each figure is used for

Density sets the weight on the BOM and feeds the load checks. A queen bed in white oak is noticeably heavier than the same bed in pine, which matters if it has to be carried upstairs assembled.

Modulus of elasticity drives every deflection check — shelf sag, rail bending under max_assembled_load. It is the number that decides whether an 900 mm shelf needs to be 19 mm or 25 mm, and the finding tells you which.

Modulus of rupture is the breaking stress, used for the margin against outright failure rather than visible sag.

Movement, tangential and radial, is seasonal shrinkage per 10% change in moisture content. Tangential movement is roughly twice radial in most timbers, which is why a flat-sawn panel moves more than a quarter-sawn one. The wood-movement checks read these together with the part’s grain to work out whether a captured panel will split its frame.

White oak at 3.50% tangential is the mover in this list; western red cedar at 1.67% is the most stable. The arithmetic is width × coefficient × (MC swing ÷ 10): a 560 mm flat-sawn white-oak panel through a 4% seasonal swing moves 560 × 0.035 × 0.4 ≈ 7.8 mm. Indoor timber typically swings 4–5% between winter and summer, so substitute your own figure — the point is that it is millimetres, not fractions of one, and a frame that did not allow for it splits.

Screw withdrawal, face and end, is graded high · medium · low · poor. The fastener checks use it, and note that every timber here rates worse in end grain than in face grain — which is why forbid_into_end_grain exists on the fixtures and why bed bolts, which thread into a steel cross dowel rather than into wood, are the right answer for a rail end.

Hardness is Janka, in newtons. It does not drive a check; it is there for choosing a timber for a surface that gets used.

Sources

Figures are at approximately 12% moisture content, from the USDA Wood Handbook (FPL-GTR-282, 2021), Tables 5-3 and 5-5, converted to SI. Movement coefficients are total green-to-ovendry shrinkage divided by 30% MC, the standard linear approximation for seasonal movement in service.

These are published material properties, not anyone’s dataset. The catalogue is CC0-1.0.

Sheet goods do not have a species

A panel behaves the way it does because of how it is built, not what tree it came from, so sheet materials carry their own properties — see Sheet goods. The one exception is sheet.veneered.mdf, which takes a species for the veneer, because the veneer is directional and the sheet has a show face.