Heritage Sash Windows
All sash windows are manufactured in-house at our London workshop using traditional joinery methods and high-quality hardwood or Accoya wood.
With over 35 years’ experience, we produce handcrafted sliding sash windows & casement sash windows for period homes, listed buildings, and properties in conservation areas. Always made to match the original detailing while meeting modern performance standards.
Sash Window Upgrades & Restoration
Where original box frames remain in sound condition, we offer a sash upgrade service that retains the existing box frame while upgrading the moving parts.
New sashes are manufactured in Accoya or hardwood, incorporating heritage double-glazed units, traditional mouldings, and full draught-proofing. This approach preserves original character while improving performance, security, and ease of use. All work is carried out to a standard suitable for listed properties and conservation areas.
Where possible, original timber box frames can be carefully restored, with sill replacements, hardwood splicing, and epoxy resin repairs used to extend their lifespan and maintain historic integrity.
Box Sash Window Replacement
Where the existing windows are beyond repair or a full replacement is preferred, we manufacture and install complete new box sash windows to match the architectural period of the property.
Each window is made in-house using traditional joinery methods, featuring solid timber frames, lead weights, pulleys, sash cords, and a range of double glazing & Vacuum glazing options.
All details, including mouldings, glazing bars, horns, and sill profiles, are faithfully reproduced to ensure a like-for-like appearance.
Our box sash windows are designed to meet the expectations of conservation officers, while providing modern standards of security, insulation, and operation.
Casement Sash Window Upgrades & Restoration
When the original timber frames are structurally sound, we can upgrade the casement sashes while retaining and restoring the existing frame.
New sashes are manufactured to match the original design and proportions, incorporating heritage double-glazed units and discreet draught-proofing.
This allows for improved thermal and acoustic performance while preserving the external appearance of the property. An approach particularly suited to listed buildings and homes within conservation areas.
Casement Sash Window Replacement
Where the existing windows are beyond repair or a complete renewal is preferred, we manufacture and install full new timber casement windows to suit the period and style of the property.
Each window is produced in Accoya or hardwood, with traditional flush casements, solid glazing bars, and a range of double glazing & vacuum glazing options.
Our casement windows are built to match original details and the requirements of conservation officers and heritage architects.
Reliable Trade Supply for Over 20 Years
Landmark is a trusted name in the supply of timber sash windows and doors to the trade.
Working with sash window specialists, builders, and architects across London and the South East.
Over 80% of our production is dedicated to trade clients, delivering consistent, high-quality joinery built to meet the demands of period homes, listed buildings, and conservation projects.
Traditional Joinery Methods
What sets Landmark apart is our ability to produce large volumes of sliding sash and casement sash windows using authentic joinery methods.
For many of our trade partners, we manufacture sliding sashes only, ready to be retrofitted into restored original frames on site. We also supply complete timber box sash window sets where required, with full frame and sash construction made to conservation standards.
Our workshop produces both box sash and casement frames daily, serving trade clients and residential homeowners.
As with all our windows, we offer flexible finishing — choose from fully finished and glazed, or opt for primed-only and unglazed, ideal for trade clients who prefer to complete glazing and hand painting in their own workshop.