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Timber box sash windows

Our timber box sash windows are individually made with the closest attention to detail to ensure that the characteristics of the original windows are preserved, with traditional ropes and pulleys, period moulding detail and profiled sash horns.

Traditional craftsmanship is combined with the latest technology and finishes, including sealed double-glazing to “A” rated specifications and an advanced microporous paint system, to provide maximum insulation and durability.

Our high performance box sash windows are expertly installed and finished with period profiled architraves and internal sill nosings, and the surrounding walls are decorated to provide you with fully completed installations.

We have experience of installing wooden windows in conservation areas and in historic properties, for which our windows are designed and glazed to requirements.

We can assist with planning applications if required.

Timber sash windows London


Accoya box sash windows London


At SPS Timber Windows we not only create beautiful timber box sash windows but ensure that their performance is optimised through the use of the highest quality timber available.

For information about Accoya® Wood, see Why timber, Why Accoya®


Draught proofing

High quality draught seals are discreetly and integrally fitted within the frames to ensure optimum thermal performance.


Glass and glazing

Our double-glazed box sash windows are glazed to “A” rated specifications, exceeding the latest building regulation requirements, to offer superior energy efficiency.

Sealed 22 mm double-glazed units, comprising of low “E” glass, argon filled “Swisspacer” bar and Pilkington Optiwhite™ extra clear, low iron glass provide an indicative centre pane U-value of 1.2 W/m2K.

We offer a wide variety of glass types to suit specific requirements, including:

  • Toughened glass
  • Laminated glass
  • Acoustic glass
    Double-glazed units can incorporate SGG STADIP SILENCE® acoustic insulating 6.8mm laminated glass (35db Rw) to provide additional sound insulation and security. The incorporation of a totally transparent interlayer absorbs sound and reduces the level transmitted through the glass, helping to keep noise in or out.
  • Obscured glass, textured glass, patterned glass, etched glass
  • Leaded glass
  • Stained glass


Our drained and vented glazing rebates allow any moisture to escape through small, concealed drainage holes, which helps to maximise the life of our double-glazed units.



We use the most comprehensive treatment and finishes for our timber sash windows to ensure their longevity and minimise maintenance.

Advanced microporous treatment and paint systems combine superior standards of extensibility, adhesion and colour retention, enabling maintenance periods to be extended and redecoration to require only one coat application.

Our windows are primed with two spray-applied coats of white primer undercoat and mid-coat and are finished with a spray-applied top coat in a white semi-gloss finish to provide the ultimate in durability and weather resistance.

Once installed, our decorators brush apply a further finish top coat to the new sash windows, architraves and sill nosings, as required, at which point the surrounding walls are also made good and decorated internally to fully complete the installation.

Specified paint colours can be colour matched.

We also offer the option of dual colour.


Sash window fittings and security

Our traditional box sash windows are fitted with high quality pulleys, ropes and weights.

Spiral spring balances can be fitted as required.

In addition to fasteners, security is provided with a set of sash stop locks fitted to each opening window.

See our sash window Fittings for examples and finishes.


Sash window styles

SPS Timber Windows can reproduce original sash windows in any style and with any feature, including vertical, decorative or Georgian style glazing bars, and curved, arched top and Gothic designs.

Or, we can produce a specific design to your requirements.

Take a look at our Gallery for examples of completed sash window installations.



SPS Timber Windows has a policy of continuous improvement. We may therefore amend our specifications accordingly.