Sash windows get condemned as beyond repair far more often than their condition actually justifies, usually by someone selling a replacement product rather than assessing the timber on its merits.
A proper assessment separates cosmetic wear, which repair fixes completely, from genuine timber decay, which sometimes means a section or the whole sash does need remaking.
What repair actually involves
A full sash repair typically includes easing and rehanging the sashes, replacing perished sash cords with new ones, draught-sealing the meeting rails and box frame, and splicing in new timber at any localised rot — usually at the bottom rail or sill, where water sits longest.
This retains the original glass, which is often old drawn or crown glass with a subtle visual character that's genuinely difficult and expensive to replicate, along with the original glazing bar proportions that new windows frequently get slightly wrong.
When timber genuinely can't be saved
Where rot has spread through a large proportion of a sash's structural sections, rather than being confined to a repairable section, a full sash replacement — remade to match the original profile — is more sensible than an extensive splice repair that will still need replacing again soon.
Frames with widespread decay in the box frame itself, not just the sashes, are a bigger job, and at that point the cost difference between a thorough repair and a matching replacement narrows considerably.
Draughts are not a reason to replace on their own
Cold air around an old sash window is almost always down to worn or missing draught seals and gaps around the frame, not a fundamental flaw in the window design. Proper draught-proofing brings an old sash close to the airtightness of many new windows without touching the glass or timber at all.
Secondary glazing is another option worth considering alongside repair, adding a significant thermal and acoustic improvement while leaving the original window completely untouched and easily reversible.
Conservation areas and listed buildings
In a conservation area or on a listed building, replacing original sash windows with anything other than a matching timber replica is very likely to need planning or listed building consent, and uPVC or aluminium replacements are routinely refused. Repair avoids this process entirely.
Even where replacement is permitted, matching the glazing bar width, horn detail and putty line of the original by eye from a standard supplier's range is harder than it looks, and a poor match is visually obvious on a period elevation.
Common questions
How do I tell if my sash windows can be repaired?+
A joiner needs to probe the timber at the sill, bottom rail and box frame with a bradawl to check for soft, decayed wood versus sound timber under old paint. Sound timber with cosmetic wear and worn cords is almost always repairable.
Is repair actually cheaper than replacement?+
Generally yes, particularly when only a handful of sashes need attention rather than a whole house of frames in poor condition. Replacement becomes more comparable in cost once several windows need full remaking rather than repair.
Will repaired sash windows be as draught-free as new double glazing?+
With full draught-sealing they get close, though a new double-glazed unit will usually still edge it on raw thermal performance. Adding secondary glazing behind a repaired sash closes most of that remaining gap.
Get your sash windows assessed
We'll check the timber properly before recommending repair or replacement, and give you a written quote for whichever route the window actually needs.