In many cases an existing timber sash and case window can be upgraded, but the correct approach depends on the dimensions, condition and historic significance of the original sashes. The aim should be to improve comfort without unnecessarily removing sound traditional fabric.
What needs to be checked first?
The sash must have enough sound timber to accommodate the glazing system safely. The depth and width of the glazing rebates, condition of the joints, strength of the meeting rails and overall weight of the new glass all matter. The cords, pulleys and counterweights may also need alteration so the upgraded sash continues to operate correctly.
What is slim-profile double glazing?
Slim-profile units are designed to reduce the visual bulk associated with conventional modern double glazing. They can be useful where a traditional appearance is important, although suitability should be assessed for each window and planning or listed-building requirements may apply. Read more about our heritage slimline double glazing.
Do the original sashes always have to be replaced?
No. Where the existing sashes are sound and their glazing bars and rebates permit an appropriate upgrade, retaining them may be possible. Where they are too slender, badly distorted or extensively decayed, new matching timber sashes—or occasionally a complete new window—may be the more practical solution.
Alternatives to double glazing
If double glazing is unsuitable, secondary glazing can improve thermal and acoustic performance while leaving the external window substantially unchanged. Professional draught proofing can also make a noticeable difference to comfort at a lower level of intervention.
Conservation and listed buildings
Alterations to windows in listed buildings and sensitive conservation settings need particular care. Requirements vary by building and proposal, so check the relevant consent position before ordering work. Our listed building and conservation-area guide explains the main considerations.
Unsure which option suits your windows? Arrange a survey and we can assess the existing timber, glazing and operation before recommending an approach.