Our Products - Casement Windows

The 50-Year Casement Window

Years of customer collaboration and advances in technology have helped us develop our bespoke 50-Year casement window into one of the highest performing on the market. While we wanted to make our windows thermally efficient, we also wanted to stay true to the heritage of the casement window. That’s why we designed our range with meticulous precision to retain the flush-line traditional appearance that helps add character to your property.

London Box Sash Windows provides a range of bespoke casement window options to suit your specific requirements. From traditional flush casement windows all the way through to bespoke modern designs.

Key Benefits

  • EXTRA DURABLE – Timber guaranteed against rot for 50 years
  • EXTREME STABILITY – 75% reduction in shrinkage and swelling
  • LOW MAINTENANCE – 3-4 times longer lasting paint finish
  • ROBUST CONSTRUCTION – Traditional mortice and tenon joints
  • SYMPATHETIC – Traditional features replicated like for like
  • HIGH PERFORMANCE – A rated double-glazed units
  • NATURALLY INSULATING – Improved thermal insulation
Benefits Chart


Timber – Accoya® Wood

Like all our premium specification products, the ‘50-Year Casement Window’ is made using the highest grade Accoya® wood on the market. Accoya® wood is the result of decades of research and development that has brought together a long-established, extensively proven wood modification technique and leading-edge patented technology – acetylation – to create a high performance wood, ideal for outdoor use and challenging applications.

Accoya® has properties that match or exceed those of the best tropical hardwoods and treated woods, yet is manufactured using wood from sustainable sources.

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

One of the most important reasons customers seek new windows is to improve sound insulation as well as thermal efficiency. At London Box Sash Windows we know that the glass used in our windows plays one of the most important roles of all. That’s why we glaze our premium casement windows with the highest ‘A’ rated double-glazed units, which exceed latest building regulation requirements.

The windows are glazed with 24mm double-glazed units, comprising of low ‘E’ glass, argon filled ‘Swisspacer’ bar and Pilkington Optiwhite extra clear, low iron glass, which provides an indicative center pane U-Value of 1.2 W/m2K.

To protect and prolong the life of our double-glazed units we have designed a unique drained and vented rebate glazing system to prevent premature failure of glazing unit seals by allowing any trapped moisture to drain through small, concealed drainage holes. Such a development has enabled us to double our guarantee against premature failure.

Our casement window range can also incorporate a variety of other glass options to suit specific requirements:

  • Toughened glass or laminated glass
  • Acoustic glass – Double-glazed units can incorporate acoustic insulating 6.8mm laminated glass (35db Rw). This product combines two sheets of clear glass bonded together with a totally transparent interlayer. The interlayer absorbs sound and reduces the level transmitted through the glass, helping to keep noise in or out
  • Obscured or textured glass
  • Stained glass
Sash Window Double Glazing Technical Data


London Box Sash Windows Teknos Low Maintenance Microporous Paint Systems

The 50 casement window is finished with the finest Teknos low-maintenance microporous paint systems, coupled with end grain sealing and highly skilled spray application, giving us an unrivalled, long-lasting paint finish. Because our sash window range is made using Accoya® exclusively, maintenance cycles are greatly extended and on redecoration only require one topcoat.

As with our box sash range, we can match to any Dulux, Crown, Farrow & Ball or RAL colour you require.

Draught Proofing

The ’50 Year Casement Windows’ come fully draught-sealed. All casement window and door sets are draught-proofed utilising Schlegal seals concealed within the stops to opening lights, ensuring optimum thermal performance.