Sash Window Timbers.

Common Timbers For Heritage Joinery

Common Timber Species for Traditional Sash Windows

A light weight timber is desirable for vertical sliding sash frames because they have to be counterbalanced.  Accoya is recommended.  Window sills (cills) should be durable and not liable to twisting or splitting. Hardwood is recommended. 

Whilst wood price is a consideration, remember that the biggest cost comes in the manufacture & installation.  At Sash Window Specialist we do not mark up premium timber and so you will only pay the difference of what the plank costs us.  The differences in pricing on a finished bespoke joinery item is very reasonable, allowing you to select the right product for your project, ensuring a long lifetime of use.

The environmental benefits of timber

Wood is naturally beautiful and versatile and is one of the best ways to address climate change.  It is renewable and abundant and as we transition to a low carbon economy, the advantages of wood are increasingly making it the material of choice for the environmentally conscious.

Accoya. - The perfect timber for sash windows?

ACCOYA Common Timbers For Heritage Joinery 1


80 years of research resulted in Accoya, a high performance wood that exceed those of the best tropical hardwoods. Using nontoxic processes fast growing pine is structurally altered to produce a stable, very durable product.

  • The manufactures guarantee against rot in its natural unpainted state for 30 years and they confidently claim at least a 60 year life cycle in painted windows.
  • Expensive initial outlay is easily recouped over time with less maintenance costs.
  • The average weight of dried timber is about 510 kg/m3.
Douglas Fir / Oregon - A timeless classic.


Pseudotsuga menziesii, Pseudotsuga taxifolia, Pseudotsuga douglasii.


A time proven durable softwood that is still popular today, however Douglas-Fir is a premium grade softwood which is reflected in the price. Grown around the world including USA, Canada, New Zealand.  Other names include Oregon pine & British Columbian pine.

  • Douglas fir is a good insulator for sound, heat and electricity. It also possesses natural fire retardancy.
  • Somewhat brittle and susceptible to splitting
  • Lots of resin – concentrated pockets are common. 
  • Highly resistant to mechanical & chemical abrasion.
  • The average weight of dried timber is about 530 kg/m3.
Redwood / Deal - Budget Timber.


Pinus sylvestris.

The most commonly encountered timber used in the construction of traditional windows in Europe, due to its continued popularity since the late seventeenth century. Know under many other names inc. Red Deal, Yellow Deal, Softwood, Scandinavian Pine, Scots Pine, Baltic Pine etc.  Deal includes several varieties of pine, fir and spruce imported from Northern Europe.

The European Redwood available today is rapid grown in sustainable plantations but not to the same quality as the old growth timbers of yesteryear.

  • Moderately resistant to decay, but paint work must be maintained in good condition.
  • Knots & resin are common.
  • Budget, paint grade softwood.
  • Light weight – The weight of dried timber is about 510 kg/m³.
Meranti - Paint grade hardwood.


Shorea spp, Shorea pauciflora, Shorea acuminata, Shorea platycarpa, Shorea platyclados, Shorea curtisii

Meranti is variable in both colour and density as there are many sub-species of tree. It is a popular, affordable South East Asian hardwood used for manufacturing windows & doors.  Often marketed as Luan or Philippine mahogany.

  • In general, Meranti is naturally resistant to decay and insect attack.
  • Does not easily take preservative.
  • Affordable, value for money hardwood.
  • The wood weighs on average 710 kg/m³ when dried.
Mahogany - Common timber in upmarket sash windows.


Swietenia macrophylla, Swietenia mahagoni. 

Occasionally used for the construction of sash windows in grand or public buildings where the figure of the grain is desirable. True Mahogany(Swietenia) is indigenous to the Americas but other species are often marketed as mahogany.

  • Very stable timber.
  • Moderately light hardwood, air-dry density is 570 kg/m3.
  • Expensive.
  • Fiji Mahogany is plantation grown. Other sources are to be avoided- CITES Appendix II listed species.
Sapele - Quality hardwood, alternative to mahogany


Entandrophragma cylindricum


A common alternative to the more expensive Mahogany. Sourced from West Africa, often marketed as African Mahogany.  Utile is a similar timber with a more intersting grain.

  • Tendency to warp.
  • Sapele makes a good durable sill.
  • Heavy wood that can add considerable weight when used for large sashes weighing about 640 kg/m³ when dried.

It can be difficult to obtain quality timber stocks (we only use certified sustainable sourced timbers ).

Oak - durable hardwood


Europe: Quercus robur, Quercus petraea, Quercus sessiliflora, Quercus pedunculata

America: Quercus spp, Quercus alba, Quercus prinus, Quercus montana, Quercus lyrata, Quercus michauxii.


Needs no introduction. European or American.

  • Waxed Oak offers a beautiful finish that’s been popular for centuries in home & furniture construction.
  • A very durable hardwood.
  • Expensive.
  • Heavy wood that can add considerable weight when used for large sashes being about 720 kg/m³. ( From Central Europe  about 672 kg/m³).
Jarrah for sash windows.


Eucalyptus marginata


A common timber in Australia

  • Very durable.
  • Tendency to split.
  • Jarrah makes a good sill.
  • Heavy wood that can add considerable weight when used for large sashes having an air-dry density about 820 kg/m3.
Common Timbers For Heritage Joinery 2


Thuja plicata.

A soft aromatic timber usually selected for a stain finish.  The wood is non-resinous & straight-grained. 

  • Red Cedar is durable & long lasting but less resistant to splitting and indentation than redwood
  • Takes stains very well.  When untreated & exposed to the weather the wood becomes silver-grey.
  • Light Weight – about 390 kg/m³ when dried.

 Timber density is quoted by our suppliers as an average, however this can vary by 20% or more.

Vac Vac Treatment

Involves the application of organic preservatives to softwood timber under low pressure.  The timber is placed in a vacuum chamber to remove air from the timber, water based preservative is then introduced, penetrating into the timber structure.   A 2nd vacuum is employed to remove the excess preservative.  

Effective for treating the sapwood of pine but not the denser heartwood, Douglas Fir or hardwoods.  Untreated painted softwood joinery can last for decades but only if the paint coating is maintained in prime condition. Vac-Vac treatment offers some protection against rot if water does penetrate into the wood.  Painters often report that this treatment can cause the paint to peel.

Acetylation Treatment – Accoya Modified Wood

Unlike pressure treatment, in which preservatives compounds are infused into wood, acetylation chemically modifies the wood. The process alters the cell structure of wood, improving its technical properties and making it much stronger and more durable resulting in better dimensional stability and decay resistance.  Acetylation reduces moisture in the cell wall to the point where there isn’t enough left to support fungal or insect development.

Read the Accoya FAQ here

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