Timber species for joinery

At a glance

US Forest Products Laboratory, Wood Handbook FPL-GTR-282 (2021): Tables 5-3 and 5-5 (hardness at 12% moisture content), 4-3 and 4-4 (shrinkage, green to oven-dry), 14-1 (decay). Density is ours from the handbook's specific gravity († calculated by its equations). Not European species; see the full table.

What each number tells you, and what it does not

Three different numbers get called "how good is this timber", and each answers a different question. A comparison is only fair when they come from one source measured one way, which is why the table below uses a single source throughout: the US Forest Products Laboratory's Wood Handbook (FPL-GTR-282, 2021).

• Hardness is resistance to denting. The handbook defines it as resistance to indentation by a modified Janka test, the load needed to push an 11.28 mm steel ball to half its diameter into the wood. The tables call it side hardness (the ball goes in across the grain) and give it in newtons and in pounds-force at 12% moisture content. It tells you about tops, treads and handles. It says nothing about stability, durability or how the timber finishes.
• Density is mass for volume. The handbook tabulates specific gravity (oven-dry mass over volume) and converts it to a density at any moisture content. Heavier timber is usually harder and stronger, but also moves more: the handbook says greater shrinkage is generally associated with greater density.
• Durability is the resistance of heartwood to decay fungi. It matters only where timber gets wet. The handbook groups species as very resistant, resistant, moderately resistant, and slightly or non-resistant. BS EN 350:2016 uses five classes, DC 1 to DC 5. The two schemes are not interchangeable and we do not convert between them.

No figure is a constant. The handbook gives a coefficient of variation of about 10% for the oven-dry density of common US species and about 15% for shrinkage. For the imported species it warns that shrinkage values were taken from the world literature and may not represent a true species average. Its own species text puts iroko at about 688 kg/m³ at 12% moisture content where the table arithmetic below gives about 660. Treat every row as an indication from clear small specimens, name the species by its botanical name, and ask the supplier for the figures for the batch.

Eighteen timbers compared

Eighteen timbers, one source, one method. The bars show side hardness in newtons; the full table adds density, shrinkage and the handbook's decay grouping. The “Across 150 mm” column is ours: how far a plain sawn board 150 mm wide changes in width for a 4-point change in moisture content, worked as width × (tangential shrinkage ÷ 30) × points ÷ 100, using the handbook's linear shrinkage relationship (Equation 4-9) with the fibre saturation point taken as 30%, as the handbook advises when it is not known. For white oak that gives 2.1 mm, against 2.3 mm from the handbook's own coefficient method used in the sheet on timber cuts.

Reading it. The three right-hand columns separate the timbers more than hardness does. Iroko is nearly as hard as white oak and moves about a third as much. American beech, white oak and sugar maple are among the hardest here and also the most mobile. Teak is softer than all of them and moves about half as much as white oak. Plain sawn boards move about twice as much as quarter sawn, which the sheet on timber cuts works through. The scatter chart puts hardness against movement for all eighteen.

What is missing. The American species are the handbook's US-grown woods, not the European ones we are most often asked for. European oak, ash, beech, sycamore, walnut and sweet chestnut are not in the tables we read, and an American oak is a different species from a European one. The page does not substitute one for the other: for those timbers, ask the partner workshop or Timber Development UK for a data sheet and name the figures' source in the specification.

Durability, moisture and where each timber can go

For a dry, heated interior, natural durability is not the deciding number, and a species rated "slightly or non-resistant" (the ashes, maples and beech in the handbook) is not a poor choice for panelling or cabinets. It matters in wet areas and outside. Two cautions apply. The ratings are for heartwood. And the handbook's own note says decay resistance may be less in contact with the ground or in warm, humid climates, with substantial variability inside a species.

Where the handbook's groupings are useful is in ruling things out. In its Table 14-1 the white oaks, black walnut, iroko, afrormosia and western redcedar are in the resistant group, old-growth teak is very resistant (young-growth teak is moderately), and sapele, African mahogany, cherry, Douglas-fir and larch are moderately resistant. Treat the grouping as a first filter and then ask the supplier for the declared durability class under BS EN 350:2016.

Movement and finishing

Movement and finish are where a handsome species becomes a problem. The movement column above is the practical one: a 150 mm board that is fitted damp and left to dry in a heated room moves by the 4-point figure, and the sheet on timber movement in panelling and veneer works the same arithmetic for a whole panel. Finishing is species-specific, and the handbook has something to say about only some of them.

Two points apply to nearly every timber. Steel wool or a steel brush leaves iron that reacts with tannins, in oak, western redcedar and many tropical hardwoods, to leave blue-black stains. And a finish is judged on the species and cut it is applied to: ask for a finished sample, as the sheet on finishes on timber joinery sets out.

Naming the timber, and substitutions

A specification that says "oak" or "mahogany" can be met by timbers that differ by a third in hardness. Name the timber by its botanical name and say the cut, the appearance class, the moisture content and the evidence. Three traps from the sources:

• Common names. The handbook lists yellow-poplar as also called tulipwood, and African and American mahogany are different woods (African mahogany is rated moderately resistant, below American mahogany). "Mahogany" alone does not say which.
• Substitutes. The handbook notes that iroko has been suggested as a substitute for teak and that afrormosia is sometimes used as one. In its tables iroko is harder than teak (5,600 against 4,400 N) and moves less (tangential shrinkage 3.8% against 5.8%), but it is not the same timber, and an afrormosia substitute carries the CITES and IUCN notes above. Agree any substitution in writing and against a sample.
• Growth and origin. Teak appears twice in the decay table, old-growth and young-growth, with different ratings. Where supply or certification matters, see the sheet on specifying FSC and PEFC.

Timber: [species by botanical name, e.g. Quercus robur or Q. petraea], heartwood [with / without] sapwood on exposed faces, cut [quarter sawn / plain sawn], appearance class [BS EN 942 class [J10]] against approved sample [ref]. Source and certification: [FSC / PEFC], chain of custody document at delivery.

Where hardness governs (tops, treads, handles): side hardness not less than [ ] N at 12% moisture content for [species], stating the test method and the source of the figure, confirmed by the partner workshop's data sheet for the batch supplied. No substitution of species without written approval against a sample.

Wet or external areas: heartwood only of [species] with declared natural durability class [DC 1 or DC 2] to BS EN 350:2016, sapwood excluded, for use class [ ] to BS EN 335, with the supplier's declaration at delivery. Edge, end grain and fixing details as shown on the shop drawing.

Timber supplied at [ ]% moisture content (tolerance [ ]%), measured and recorded on delivery and before fixing; finish [system] applied to the approved sample of the same species and cut. Steel wool and steel brushes not to be used on [oak / tannin-rich species].

Standards and sources

• USDA Forest Products Laboratory, Wood Handbook, FPL-GTR-282 (2021): Tables 4-3, 4-4, 5-3, 5-5, 14-1; chapters 2, 4, 14, 16. Read 5 Nov 2026.
• BS EN 350:2016 Durability of wood and wood-based products: named, not read; class names from the BWF.
• BS EN 335 (use classes) and BS EN 942:2007 (appearance classes): named, not read.
• British Woodworking Federation, Choose Wood: Durability: class names; heartwood and sapwood.

Questions we are asked

What is the Janka hardness of oak?

In the US Wood Handbook, white oak (Quercus alba) is 6,000 N (1,360 lbf) and northern red oak (Quercus rubra) is 5,700 N (1,290 lbf), side hardness at 12% moisture content. European oak is not in the tables we read, and other published charts give different figures for many species, so name the species by its botanical name and the source of the figure.

Which timber is the most stable for joinery?

In the tables we read, iroko moves least (tangential shrinkage 3.8%), then African mahogany (4.5%), western redcedar (5.0%) and teak (5.8%). American beech (11.9%), white oak (10.5%) and sugar maple (9.9%) move most. Cut matters as much: a plain sawn board moves about twice as much across its width as a quarter sawn one.

Does natural durability matter for interior joinery?

Only where the timber gets wet. The Wood Handbook says serious decay occurs only above the fibre saturation point, about 30% moisture content, and fully air-dried wood of 20% or less has a reasonable margin. In a dry heated room choose on appearance, hardness, movement and finish. In a bathroom, spa or outdoors, durability counts, for heartwood only.

Is a higher hardness always better?

No. Harder timbers dent less, but the hardest in the tables are often the most mobile and can be harder to work and finish. Sugar maple is 6,400 N and shrinks 9.9% tangentially; iroko is 5,600 N and shrinks 3.8%. Hardness says nothing about durability.

What does the BS EN 350 durability class mean?

BS EN 350:2016 classifies the natural durability of wood to biological agents in five classes, from DC 1 very durable to DC 5 not durable. The ratings refer to heartwood. We have not read the standard, so ask the supplier for the declared class for the species and what it is based on.

Is tulipwood the same as yellow-poplar?

The Wood Handbook says yellow-poplar (Liriodendron tulipifera) is also known as tulipwood. A specification should still give the botanical name, because trade names are used for more than one timber.