Methodology
About this data
Where the numbers come from, what they mean in practice, and how to use them responsibly.
A note on who made this
I drive timber for a living. Five days a week I'm collecting from sawmills, delivering to merchants, dropping loads at building sites, joiners' workshops, and the occasional DIYer who's taken on something ambitious. I touch timber, smell it, and think about it constantly — but I'm not a buyer, a specifier, a scientist, or a trained forester.
Outside of work I have a 600 sq ft wood workshop where I make things — hand-painted signs in particular — so I also use timber from the maker's side of the bench. That combination of seeing how it moves through the supply chain and how it actually behaves on a workbench is what this site comes from.
Mill & Merchant is a personal project. The species data is curated from the best available public sources — I do research things, cross-reference where possible, and try to present information in a way that's genuinely useful for people who work with wood rather than study it. It may develop paid features in the future, but the knowledge base will stay free. Where I've made editorial judgements or simplifications, I've tried to flag them.
If something is wrong, please tell me. I'd rather have an error corrected than quietly perpetuate it.
Primary data sources
Mechanical and physical data for each species is drawn from peer-reviewed reference sources and established forestry databases. Where values differ between sources, the most widely cited figure is used or the range is noted.
Density, Janka hardness, modulus of rupture, elastic modulus, crushing strength, and shrinkage values.
Tangential, radial, and volumetric shrinkage coefficients. T/R ratio. Green moisture content.
Natural durability classes 1–5 (Very Durable to Perishable) for heartwood. Durability applies to heartwood only — sapwood is generally non-durable regardless of species.
Assessments are based on the most recent published IUCN evaluation for each species.
Appendix I, II, III listings, or Unlisted. CITES status affects commercial trade — check with your supplier for current compliance requirements.
Scientific names, family, genus, and accepted nomenclature.
UK-specific availability, typical commercial sizes, and market notes.
Fundamental wood anatomy, shrinkage, movement, and working properties.
How shrinkage & movement values work
Shrinkage values (tangential %, radial %) represent the total dimensional change from green (freshly felled) to oven-dry — a range of roughly 28–30% moisture content change. They do not represent movement per 1% change in moisture content.
The Wood Movement Planner tool converts these values into a practical sensitivity coefficient by dividing by the fibre saturation point (~28%), then applies it to your board width and moisture content swing to give an estimated movement in mm.
The T/R ratio (tangential ÷ radial) indicates how unevenly a species shrinks. A higher ratio means a greater tendency to cup across the width when moisture changes. Ratios close to 1.0 indicate more stable, dimensionally predictable species.
Durability ratings — what they mean
Durability classes under BS EN 350 apply to the heartwood only and describe resistance to fungal decay (rot). They do not describe resistance to insects, UV degradation, or mechanical wear.
| Class | Rating | Typical service life (untreated) |
|---|---|---|
| Class 1 | Very Durable | 25+ years in ground contact |
| Class 2 | Durable | 15–25 years |
| Class 3 | Moderately Durable | 10–15 years |
| Class 4 | Slightly Durable | 5–10 years |
| Class 5 | Perishable | < 5 years |
Caveats & responsible use
- All data is indicative. Values represent typical published figures — individual boards will vary based on growth conditions, sawing pattern, and drying history.
- Mechanical properties (Janka hardness, MOR, MOE) are typically measured on clear, defect-free specimens. Knotty or irregular grain will perform differently.
- Do not use movement planner results as the sole basis for structural decisions. Consult a structural engineer for load-bearing or safety-critical applications.
- IUCN and CITES status can change. Always verify current listings before purchasing commercially traded species, particularly for export or construction projects.
- UK availability and pricing notes reflect general market conditions and may not reflect current supply chain constraints.
Errors & corrections
If you spot an error in a species value, an outdated IUCN/CITES status, or a missing citation, please get in touch. The species library is updated regularly — corrections from practitioners, researchers, and forestry professionals are always welcome.