Accoya Sash Windows: Pros, Cons and Cost

Accoya is a fast-growing softwood that has been treated to make it far more stable and rot resistant than ordinary timber. For sash windows, that means less swelling and sticking, longer-lasting paintwork and a long manufacturer guarantee. Accoya sash windows usually sit in the hardwood price range, typically £1,800 to £3,500 per window fitted. This guide explains what Accoya is, its pros and cons, and whether it is worth the extra cost.

What is Accoya?

Accoya is radiata pine that has been acetylated, a process that changes the structure of the wood so it absorbs much less water. Because timber movement and rot are both driven by moisture, acetylated wood swells and shrinks far less and is very resistant to decay. The manufacturer, Accsys, offers a guarantee of up to 50 years for Accoya used above ground. It is made from sustainably grown timber.

Accoya compared with other timbers

	Softwood	Hardwood (such as oak or sapele)	Accoya
Typical cost per window, fitted	£1,200 to £2,500	£1,800 to £3,500	Similar to hardwood
Stability (swelling and sticking)	Moderate	Good	Excellent
Rot resistance	Needs good maintenance	Good	Excellent
Paint life	Shortest	Good	Longest of the three
Weight	Light	Heavy	Light

The pros of Accoya sash windows

• Smooth running all year: because it barely moves with the seasons, sashes are less likely to stick in winter or rattle in summer.
• Longer paint life: stable timber puts less strain on paint, so finishes last longer between redecorations.
• Rot resistance: sills and bottom rails, the usual weak points, last much longer.
• Light weight: lighter sashes are easier to balance, especially with heavier double glazing.
• Sustainability: made from certified, fast-growing timber.

The cons and common problems

• Cost: you pay a premium over standard softwood.
• Corrosion of fixings: acetylated timber is mildly acidic, so manufacturers use stainless steel or coated fixings. A good joinery firm will already do this.
• Not traditional: for a listed building, a conservation officer may want the same species as the originals. Check before ordering. See our listed building windows guide.
• Quality depends on the joiner: Accoya does not make up for poor joinery, glazing or painting.

Is Accoya worth it?

Accoya is usually worth it if you want new timber sash windows with the lowest maintenance and the longest life, especially on exposed elevations that take the weather. If budget is tight, well-made softwood windows with a good paint system and regular maintenance can also last for decades.

Compare all the options in our guide to timber sash windows: softwood, hardwood or Accoya, and see uPVC vs timber sash windows if you are still deciding between materials.

Questions to ask a supplier

• Is the whole window Accoya, or only certain parts?
• What fixings and ironmongery do you use with Accoya?
• What paint system is applied, and how many coats are factory-finished?
• What guarantee covers the timber, the paint and the glazing?
• Can I see examples of your Accoya windows that have been fitted for a few years?

Compare installers offering Accoya sash windows near you. For full prices, see our sash window replacement cost guide.

Frequently asked questions

How long do Accoya windows last?

Accoya is guaranteed by its manufacturer for up to 50 years above ground, and well-made, well-painted Accoya windows can last longer.

Are Accoya windows more expensive than hardwood?

They are usually priced in a similar range to hardwood windows, typically £1,800 to £3,500 per window fitted, and more than standard softwood.

Does Accoya need painting?

Yes. Accoya is normally painted or stained, but because it moves so little, the finish typically lasts longer than on other timbers.

Can I have Accoya sash windows in a conservation area?

Usually, yes, because they look like traditional timber windows. For listed buildings, check with your council, as the original timber species may be required.

Sources

Price ranges from the Best Builders sash window cost guide (September 2026). Guarantee details from Accsys product information.