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When looking to replace your timber windows or doors, it is important to consider the different timber options that companies may use in their quotations.

Timber selection is probably the most important element in quality window manufacture. With regular maintenance, windows built using the best timber should last a lifetime and beyond. Timber should be chosen for strength, durability and stability.

Timber Durability Chart

Timber Durability Chart by Gate Expectations by Inwood. Click on the image to see the information more clearly.


Accoya© is an engineered timber grown from sustainable sources, and treated with ascetic acid under high pressure. This treatment reaches the core of the timber, stabilising and preserving it. Accoya© is extremely durable (class one durable), making it ideal for extreme weather conditions. In fact, other timbers are often rated against Accoya©, with Accoya© being used as the benchmark against which other treatments and modified timbers are measured.

The high stability helps ensure that windows and doors open easily all year round. Accoya© wood also forms an effective barrier to insect attack, making it less prone to rot than other timbers.

Accoya© is fully sustainable and comes with a 50 year anti-rot guarantee.

Siberian Larch

Larch timber is a species of tree grown in arctic conditions and under much duress. The wood is a moderately durable (class three - four durable), Softwood timber, which is both stable and resistant to decay. Similar to hardwoods, Siberian Larch does not require any preservative treatment, and is rot resistant. The timber is extremely hard, making it one of the toughest and most durable softwoods.

European Redwood

Redwood, also referred to as Scandinavian Pine, is also a Softwood timber. The heartwood variety is pale to dark reddish brown. It is a stable timber that is moderately resistant to decay and insects (class four durable). The timber has a high resistance to shrinking and warping compared to other common softwoods.

Red Grandis

Red Grandis is a versatile, stable, Hardwood timber (class three durable). Similar to Siberian Larch, Red Grandis is moderately durable and resistant to insects and decay. Grown in South America, the timber has a good consistency in colour, appearance, and evenness of grain.


Sapele timber, also known as Sapele mahogany, is a reddish-brown hardwood. Sapele offers many of the same characteristics as Genuine Mahogany that makes it ideal for many interior and exterior applications. The timber is stable, moderately to very durable against decay (class three durable), and moderately resistant to insects. It is also ideal for painting, due to its fine graining.

However, unlike genuine Mahogany, Sapele is a timber that can be sustainably sourced, making it a great choice for the environmentally conscious customer.

European Oak

European Oak is both stable and very durable (class two durable), making it an excellent option for timber windows and doors. European Oak often also comes from sustainable sources, so it is also environmentally friendly.

The downside to oak is that it is very expensive. Please note, that if you are offered American White Oak for external windows or doors, it is not considered suitable for manufacturing external joinery.

The Sash Window Workshop

At The Sash Window Workshop we believe that it is important to use timber that is designed to last, allowing our customers to feel confident that their new windows and doors are made to the highest quality.  We therefore would suggest that customers use a class one or class two durable timber when replacing their windows and doors.

We use Accoya© as our preferred timber and also like to work with European Oak. These timbers are reasonably forgiving of any subsequent lack of maintenance or neglect and will last a lifetime. For window cills we normally use Sapele, as a high quality, sustainable timber.

We are proud to be FSC® certified, highlighting that we comply with the highest social and environmental standards.

To find out more about the timber we use, or to obtain a free quotation for high quality replacement timber windows and doors, please contact our team on: 01344 868 668.

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