Draught-proofing an existing sash window in London typically costs £250–£450 per window, a fuller restoration with new cords and re-glazing runs £400–£900 per window, and a full replacement sash built to match the original runs £900–£1,600 or more, so a typical Victorian terrace with 8-10 windows can land anywhere from around £2,500 for draught-proofing the lot to £9,000–£16,000 for a full set of bespoke replacements. Before any of that, the single most important thing to check is whether the property is in a conservation area or has an Article 4 direction, because that can rule out a straightforward double-glazed replacement entirely and push you toward repair plus secondary glazing instead, regardless of budget. This guide covers what drives the price up or down, the planning rule that trips up most homeowners, the three realistic options and when each applies, what to expect on the day, and where to go next once the windows are sorted.
Sash Window Repair Cost Overview
Prices in London run higher than the national average because of labour rates and access, sash window work in inner London typically costs 30-50% more than the same job in much of the rest of the country. Draught-proofing alone, brush-pile seals routed into the staff bead and parting bead with the sash out of its frame, is the cheapest and fastest-payback option at £250–£450 per window. A fuller restoration covering cord replacement, easing, re-puttying and repainting where the timber itself doesn't need cutting out typically runs £400–£900 per window, with an extra £150–£250 on top for any section that needs splicing with new timber where rot has set in. Where a sash is too far gone to repair, a bespoke like-for-like replacement, matched horns, glazing bars and putty line, costs £900–£1,600 or more per window depending on size and whether it's single glazed or fitted with slimline double glazing units.
For an 8-10 window Victorian or Edwardian terrace, that scales to roughly £2,000–£4,500 for draught-proofing across the whole house, £3,200–£9,000 for a fuller restoration, or £7,200–£16,000 for a full set of bespoke replacements, though very few houses need every window fully replaced at once, most jobs end up a mix of draught-proofing on the sound sashes and restoration or replacement only where a window has genuinely failed.
London Sash Window Costs, Per Window (2026)
Item
Typical range
Notes
Brush-pile draught-proofing
£250–£450
Existing sash in reasonable condition
Sash cord replacement (all four cords)
£120–£150
Cheaper for one or two cords
Full restoration (cords, easing, re-glazing, repaint)
£400–£900
Timber sound, no splicing needed
Timber splicing repair (rotten sill or bottom rail)
+£150–£250
Added to the restoration cost above
Bespoke like-for-like replacement sash
£900–£1,600+
Larger windows and double glazing at the top end
Secondary glazing (behind original sash)
£350–£600
Insulation/noise route, doesn't alter the sash
General market guidance based on 2026 UK cost-guide sources, not a fixed quote. Actual pricing depends on window size, condition, access and finish specified, and should be confirmed against a survey of your specific windows.
The Rule That Catches Most Homeowners Out
The single biggest thing that changes what's actually possible, not just what it costs, is whether your property sits in a conservation area, is listed, or is a flat rather than a freehold house. On a freehold house outside a conservation area, permitted development rights usually let you replace a sash window like-for-like without planning permission, provided the opening's size and character don't change. Inside a conservation area, many London boroughs apply an Article 4 direction that specifically removes those permitted development rights for windows, meaning even a timber-for-timber replacement can need planning permission, and a standard double-glazed unit is frequently refused on a street-facing elevation because it visibly changes the glazing bar proportions and reflectivity of the glass.
Flats are a separate problem again: a flat has no permitted development rights of its own regardless of conservation area status, so replacing windows in a converted Victorian or Edwardian house split into flats generally needs planning permission from the council and, separately, consent from the freeholder, since front-elevation windows are usually treated as shared building fabric under the lease. The practical result is that homeowners who assume 'timber means it'll be fine' sometimes find a straightforward-looking replacement refused at application stage, or challenged by enforcement well after the work is done. Checking conservation area and Article 4 status with the local planning authority before committing to a full replacement, rather than after ordering the windows, avoids that entirely.
Draught-Proofing, Restoration or Replacement: Which Applies
Draught-proofing: when the timber is sound
If a sash rattles in the wind or lets a draught through around the meeting rail but opens and closes freely once eased, and there's no rot in the sill or bottom rail, draught-proofing on its own is usually the right call. It's the cheapest option, the fastest to carry out, and typically pays for itself in reduced heating costs faster than any other measure covered here.
Restoration: when there's wear but no structural failure
Where cords have snapped, the sash has been painted shut for years, or putty has perished and let water in without yet causing serious rot, a fuller restoration addresses the underlying mechanical problems while keeping the original glass and glazing bar pattern intact. This is usually the right route for most original Victorian and Edwardian sashes that haven't been neglected for decades.
Replacement: when timber has genuinely failed
Where rot has spread through most of the sash or box rather than being confined to a section that can be spliced, a bespoke like-for-like replacement built to match the original is the sensible option, and on a conservation area property it's also usually the only option planning will approve, since it preserves the original appearance even though the timber itself is new.
What to Expect on the Day
Each sash is usually taken out of its box to be worked on properly, which means removing the staff bead and, where needed, the parting bead to free the sash from its cords. Expect some disruption to the room while a window is out, typically a few hours for draught-proofing or a day or more per window for a fuller restoration once you factor in puttying and paint drying time. Sash cords are cut and the counterweights lowered before a new cord is fitted and knotted to hold the sash at the correct height, then the sash is re-hung and tested through its full range of movement before the beads are refitted. Where re-puttying is involved, the putty needs several days to skin over before it can be painted, so a fully restored sash often needs a return visit for final painting rather than being finished in one visit.
What to Do Once Your Windows Are Sorted
If heat loss or noise is the real complaint rather than the windows' condition, it's worth looking at secondary glazing alongside, or instead of, replacing the sashes themselves, which we cover in more detail on our eco retrofit and secondary glazing page. Once windows are restored, matching internal joinery, doors, skirting and architrave, often needs attention at the same time in a Victorian or Edwardian house, which we cover on our sash windows and internal joinery page alongside staircase repair and period door fitting.
Questions
Frequently asked questions
Is it cheaper to repair or replace a sash window?
Repair is almost always cheaper, £400–£900 for a full restoration versus £900–£1,600 or more for a bespoke replacement, and it's usually the only option available on a conservation area property anyway. Replacement only makes sense where rot has spread through most of the sash or box.
Can I fit double glazing to an original sash window in a London conservation area?
Sometimes, but check first. Many boroughs accept slimline double glazing that closely matches the original glazing bar pattern, particularly on rear elevations, but standard double glazing is often refused on street-facing elevations. Confirm with the local planning authority before ordering.
How long does sash window draught-proofing take?
Typically half a day to a full day per window once the sash is out of the frame, so a house with 8-10 windows is usually a job of several days rather than weeks.
Why has my sash window been painted shut?
Usually from decades of gloss paint applied without stripping back old coats first, building up in the channel between the sash and its box. It's a mechanical problem, not proof the window is beyond repair, and is fixed by easing the sash rather than replacing it.
Is secondary glazing a good alternative to replacing my sash windows?
Yes, for most conservation area properties. Secondary glazing costs £350–£600 per window and improves insulation and noise without altering the original sash, which makes it far easier to get approved than a replacement.
Do I need planning permission to repair my sash windows?
No, like-for-like repair, draught-proofing and re-glazing don't usually need planning permission since the external appearance and opening size don't change. Full replacement is the stage that can need consent, particularly on flats or conservation area houses.
What's the most common reason a sash window needs repair rather than just draught-proofing?
Rot in the sill or bottom rail from repeated water exposure, or a snapped sash cord leaving the window unable to stay open, are the two most common reasons a window needs more than draught-proofing alone.
Get a free, no-obligation quote from Lian Construction
Send the site address, photos if available, and a short description of the work. Lian Construction surveys London properties in Kingston upon Thames and across all boroughs, then provides a clear written quote before any work starts.