Accoya and other modified timbers carry a higher raw material cost than standard softwood because of the acetylation process itself, and that base cost is before any machining, finishing or fixing work is added.
Once you're past the raw material, the same variables that move any joinery quote apply, but a couple of them matter more here because of the warranty conditions attached to the product.
Raw material and section size
The acetylation process adds a fixed cost per cubic metre over untreated softwood, so larger sections and longer clear lengths cost proportionally more, the same as with any timber, but starting from a higher base figure.
Wastage from complex profiles or curved sections is more expensive to absorb here than with cheaper timber, so a design with a lot of shaping will show a bigger cost jump moving from standard softwood to modified timber than a simple, straight-run item would.
Coating system and fixings
The approved coating system for modified timber is often a specific, higher-performance product rather than a standard trade paint, and using it correctly — including the right number of coats and cure times — adds labour and material cost beyond what a standard softwood finish schedule would need.
Fixings have to match the manufacturer's specification, usually stainless steel, and using anything else to save cost risks both the fixing's performance and the product warranty, so it shouldn't be treated as an area to economise.
What a cheaper quote has usually substituted
The most common substitution we see is a lower-cost, non-approved paint or stain system used to bring the price down, which can look identical on the day of installation but risks both adhesion and warranty cover further down the line.
The other common shortcut is specifying modified timber only where it's visible and reverting to standard treated softwood for hidden sections of the same frame, which undermines the dimensional stability the product was chosen for in the first place.
- Raw material
- Higher base cost per cubic metre than untreated softwood
- Coating system
- Manufacturer-approved products needed to keep warranty valid
- Fixings
- Stainless steel specified — swapping this voids warranty conditions
- Wastage
- Complex profiles cost more to absorb given the higher base material price
Site tolerances and delivery lead times
Modified timber sections are typically machined to order rather than held as generic stock in every size, so lead times from order to delivery are usually longer than for standard softwood, and a quote that promises a very fast turnaround on a bespoke modified timber item is worth double-checking against the supplier's actual lead time.
Because the timber holds its dimensions so precisely once acetylated, on-site tolerances for openings have to be accurate too — a frame cut to a tight, confident tolerance won't take up a generously oversized or undersized opening the way a more forgiving, moving timber might on site.
Common questions
Why is Accoya so much more expensive than treated softwood?+
The acetylation process itself adds cost to every cubic metre before any joinery work begins, and that cost is reflected through to the finished item regardless of the design.
Can I mix Accoya with standard softwood on the same frame to save money?+
It's possible but it undermines the point of specifying the modified timber, since the standard softwood sections will still move and age at their own rate. We'd rather tell you honestly whether the whole item needs it or whether a cheaper timber suits the job throughout.
Does using a cheaper paint on Accoya actually save money long term?+
No — if it isn't the manufacturer-approved system it can affect both adhesion and any warranty cover, meaning a coating failure later costs more to put right than the saving made at the time.
Get an itemised quote for modified timber joinery
We'll set out material, coating and fixing costs separately so you can see exactly what you're paying for.