Accoya Acetylated Radiata Pine
Also known as Accoya, acetylated radiata pine, acetylated wood · Botanical Pinus radiata
Revision history
- — Data re-verified in site-wide audit (formulas, sources, durability classes)
- — Working properties and comparable-species data cross-checked against listed sources
About Accoya Acetylated Radiata Pine
Accoya is radiata pine (Pinus radiata) that has been acetylated — soaked through with acetic anhydride so the wood's water-loving hydroxyl groups are converted to acetyl groups. Nothing toxic is added; acetyl groups already exist in every tree. The result is acetylated wood that barely absorbs moisture, which is why it carries EN 350 durability class 1 — a step above teak — and a 50-year above-ground service claim, from a fast-grown New Zealand plantation softwood. Movement in service drops by roughly three quarters: radial shrinkage near 0.7%, tangential near 1.5%, which is why joiners specify Accoya radiata pine for painted windows, doors, decking and cladding where nothing is allowed to move. If you are weighing Accoya against thermally modified timber: thermal modification reaches class 2 by heat and loses some strength doing it, while Accoya reaches class 1 chemically and keeps the strength of the base pine — but it costs considerably more, so thermally modified timber usually wins on decking value and Accoya on joinery that must hold paint and dimension for decades. Two practical notes from the trade: use stainless (A2/A4) fasteners, because the acetylation leaves the wood mildly acidic, and treat the 710 lbf hardness honestly — it is still a softwood underfoot. Figures here reflect the base species and published Accoya data; verify against the current datasheet for certified work.
(3,158 N) and a density of about 0.51 g/cm³. It is produced in the Netherlands from plantation-grown radiata pine.Tangential movement of 1.5% against 0.7% radial puts the T/R ratio at 2.14. That is the ratio to watch: it predicts cupping in wide flatsawn boards better than either figure alone. Its fibre saturation point is near 12%. Below it there is little movement to manage — 1.5% tangential — though the 2.14 T/R ratio still rewards sealing both faces.14 means it still cups if only one face is sealed.
At 510 kg/m³ a cubic metre of Accoya Acetylated Radiata Pine weighs about 510 kg air-dry — that figure, the 1.5% tangential and 0.7% radial movement and the 710 lbf hardness are the three inputs the calculators below actually consume. Select Accoya Acetylated Radiata Pine in any of them to get species-specific results for weight, moisture, shrinkage and hardness.
Working properties
How Accoya Acetylated Radiata Pine behaves at the bench and on the machine, drawn from Accsys technical data and independent modified-timber research.
Durability & use classification
Accoya is durability Class 1 (EN 350) — matching or bettering teak — and it earns that chemically, not by density. Radiata pine is acetylated with acetic anhydride, converting the wood's water-loving hydroxyl groups to acetyl groups so it barely absorbs moisture. Nothing toxic is added; acetyl groups occur naturally in all wood. Accsys warrants it 50 years above ground and 25 years in ground or fresh water. A necessary clarification: Accoya is acetylated, not thermally modified — it is not a ThermoWood product, despite being grouped with modified timbers.
Typical applications & suitability
Indoor Outdoor — Built for exterior use, and unusually for a modified softwood it keeps the base pine's strength.Exceptional dimensional stability — a 145 mm board moves about 3.6 mm across its full moisture range, against roughly 11 mm for Douglas fir at the same width — which is why it is specified where a painted joint must simply stay shut.
Documented end-uses: exterior windows and doors (its flagship application), cladding and rainscreens — boards up to 200 mm wide, beyond the usual softwood limit — decking, external joinery and trim, bridges and civil works, and shou-sugi-ban charred finishes.
Comparable species
Species closest to Accoya Acetylated Radiata Pine by density, hardness, stiffness and bending strength, computed directly from the Vriksai species dataset rather than hand-picked.
Trade alternatives. Compare it against thermally modified timber such as ThermoWood Pine or ThermoWood Oak: ThermoWood reaches Class 2 by heat and gives up some strength doing it, while Accoya reaches Class 1 chemically and keeps its strength — at a considerably higher price. For naturally durable routes, Sweet Chestnut or Western Red Cedar.
Alternatives to Accoya Acetylated Radiata Pine
Accoya Acetylated Radiata Pine measures 710 lbf Janka at 0.51 g/cm³, EN 350 durability Class 1, movement rated Exceptional. Accoya Acetylated Radiata Pine is a modified timber: its durability comes from process, its strength from the base species. Substitutes are matched on both, not on the treated figure alone. Read the numbers against the Janka scale and EN 350 durability classes.
Thermal modification lowers hardness slightly, so if the treated figure is short of what the job needs, these are the harder options at comparable service durability.
Lower-hardness options at similar treated durability — usually cheaper per m³ and faster through the shop.
If Accoya Acetylated Radiata Pine is unavailable and the specification cannot change, these are the nearest substitutes across hardness, density, movement, stiffness, bending strength and durability class together — not on any single property. Lower distance means a closer match.
Computed from measured properties only — hardness, density, movement, stiffness, bending strength and EN 350 class. Price, availability and appearance are never inputs. Figures are representative values, not consignment absolutes: two species within a few percent are equivalent until verified on the material. Full method and the rules the engine cannot break.
Comparing modified timber to unmodified is a comparison of process as much as species — treatment class sets the durability, the base species sets the strength. Compare directly before substituting.
Compare Accoya Acetylated Radiata Pine side by side
Modified against unmodified, and modification class against class — the comparisons that matter for treated timber. Every pairing shows the measured figures side by side; full matrix in the comparison index.
Calculators relevant to Accoya Acetylated Radiata Pine
Includes the thermal-modification tools, since Accoya Acetylated Radiata Pine behaves by treatment class as much as by species. Full set in the tool index.
Understand the figures
ThermoWood species guide — Thermo-D/Thermo-S treatment classes · Janka hardness scale — how the lbf figure is measured · Wood density reference — oven-dry vs air-dry basis · Moisture content — EMC, FSP and service conditions.
Further reading. What is ThermoWood? · Wood moisture content explained · How to calculate board feet.
Common questions about Accoya Acetylated Radiata Pine
unverified no published source for this figure · calc derived from the figures above · — no published source found