Our Products - Sash Windows

The 50-year sash window

Because London Box Sash Windows is a manufacturer we’re able to design your sash windows to suit your specific wants and needs. You can choose from a combination of premium, standard or economy materials to create the perfect sash window for your circumstances. Customer confidence is everything to us and with nearly 40 years of research and development we have designed our sash window range to incorporate important elements of our customers’ feedback. With longevity and performance being key, we use tried and tested traditional joinery techniques, combined with high performance A-Rated double-glazing, polypropylene draught sealing and the finest quality low maintenance micro-porous paint system, ensuring your sash windows stand the test of time.

Click on the highlighted areas to take a closer look at our premier box sash window features.

Click on the highlighted areas to take a closer look at our premier box sash window features.

Key benefits

  • ULTRA DURABLE – Timber guaranteed against rot for 50 years
  • EXTREME STABILITY – 70% to 80% reduction in swelling & shrinkage
  • LOW MAINTENANCE – Paint finish that lasts 3-4 times longer
  • ROBUST CONSTRUCTION – Mortice & tenon joints used
  • SYMPATHETIC – Traditional features sympathetically replicated
  • HIGH PERFORMANCE – A rated double-glazed units
  • NATURALLY INSULATING – Improved thermal insulation
Benefits Chart


Timber – Accoya® Wood

Because we know you want your windows to last we can source the highest quality woods available for the construction of your sash windows. Now 95% of all our sash windows are made from the best wood available on the market – Accoya® wood. Accoya® wood is the result of 80 years worth of continuous research and development of a proven wood modification process – acetylation – which has created the highest performing timber on the market.

Accoya® wood is created from super sustainably sourced wood. Accoya’s properties exceed the very best non-sustainable hardwoods available on the market. See below for some of its performance benefits.

Performance benefits

Performance Benefits for Sash Windows & Casement Windows: Outstanding Durability


50 years above-ground durability and 25 years in-ground / freshwater durability.
Class 1 durability – matching (and even passing) the durability of hardwoods
such as Jarrah, Rosewood and Teak.
Performance Benefits for Sash Windows & Casement Windows: Dimensional Stability


Swelling and shrinkage reduced by 75% or more.
Doors and windows open effortlessly all year round. Reduced maintenance
costs because paints and varnishes last up to 4 times longer.
Performance Benefits for Sash Windows & Casement Windows: Retained Strength & Hardness


Acetylation process does not compromise the wood's strength.
Hardness is increased – Accoya® wood is 3 times harder than
Western Red Cedar and 1.5 times harder than Radiata Pine.
Performance Benefits for Sash Windows & Casement Windows: Consistent Quality Throughout


Each production batch sampled to ensure consistent treatment quality.
No need to apply chemical preservatives to cut or planed surfaces as
treatment goes right to the core.
Performance Benefits for Sash Windows & Casement Windows: Perfect For Coating


Easier to coat – less preparation and sanding between coatings required.
Improved dimensional stability and UV resistance improves the lifespan
of coatings. Perfect for transparent, translucent and opaque coatings.
Performance Benefits for Sash Windows & Casement Windows: Non Toxic & Recylable


Accoya® wood is non-toxic, no leeching of harmful chemicals.
Accoya® wood can be reused and recycled.

Glass & Glazing

At London Box Sash Windows we know that the glass that’s used in your sash windows has one of the most important roles of all. We know you want to increase your quality of life and reduce energy costs by improving thermal performance. That’s why you have the option of glazing your sash windows to ‘A’ rated specifications, exceeding the latest building regulation requirements.

Your sash windows are glazed using the highest-performance 24mm double-glazed units. They have 16mm argon gas filled cavities, with a white Warmedge ‘Swisspacer’ bar dividing the outer and inner pane, giving the double-glazed units optimum thermal performance. The double-glazed units provide an indicative centre pane U-Value of 1.2 W/m2K. You can also incorporate other depths of double glazed units, including Slimline DGUs that can be used in certain conservation areas.

To protect and prolong the life of your double-glazed units you also have the option of incorporating London Box Sash Windows unique drained and vented rebate glazing system to prevent premature failure of your glazing unit seals by allowing any trapped moisture to drain through small, concealed drainage holes. This has allowed us to double your guarantee against premature failure.

Your sash windows can also incorporate a variety of other glass options to suit your specific requirements:

  • If security is an issue Laminated security glass can be used
  • For safety toughened glass would be installed
  • To reduce noise pollution you can use Acoustic Glass – Your Double-glazed units can incorporate acoustic insulating 6.8mm laminated glass (35db Rw). Acoustic glass combines two sheets of clear glass bonded together with a totally transparent interlayer. The interlayer absorbs sound and decreases the level transmitted through the glass, keeping the noise either in or out.
  • Textured or Sandblasted glass for privacy
  • Traditional Stained Glass
Sash Window Double Glazing Technical Data


London Box Sash Windows Teknos Low Maintenance Microporous Paint Systems

One of your biggest concerns has always been having to repaint your windows every couple of years. To minimise this requirement we spray finish all your Accoya® sash windows with the finest Teknos low-maintenance microporous paint systems, coupled with end grain sealing and highly-skilled spray application, giving you an unrivalled, long-lasting paint finish. Because the majority of your premium sash window are made using Accoya® exclusively, maintenance cycles are greatly extended and on redecoration only require one topcoat.

You also have the option of colour matching any Farrow & Ball, Dulux, Crown or RAL colour.

Draught Proofing

Our premium sash window range comes fully draught-sealed. They have a perimeter brush pile polypropylene stripping, discreetly contained within concealed carriers installed to all staff and parting bead, maximising thermal and sound efficiency.