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Renovating Sash Windows

Period house with repaired sash windows
(Image credit: Jeremy Phillips)

The replacement of sash windows is, in many cases, completely unnecessary. There are very few instances where damage and decay cannot be repaired using the right knowledge and tools.

In cases where it is possible to carry out the repairs on a DIY basis, make sure you feel confident in your skills and have the right equipment for the job. If not, get in touch with a sash window specialist, or find a skilled carpenter who has examples of previous window work they can show you.

Repair work will depend on the damage. Decaying timber, broken sash cords, damaged pulleys and broken glass, will all need replacing.

Then, the windows will need to be sanded back, primed and repainted — these are simple jobs for any DIYer. Old paint can be removed with acid such as Nitromors, or a heat gun.

Costs of repairing sash windows

Prices will vary based on the extent of the damage:

  • For a recondition and new draught seals (this may not include stripping, priming and painting) = £250 per sash
  • Box sash window replacement = £1,200
  • Double-glazed sash replacements only, to fit into existing frames = £500 per sash

Repairing sash windows step-by-step

Although the process will vary depending on the damage to your window, in general repairs follow this pattern:

  1. The sashes are removed from the frame
  2. The glass is removed and the old putty can be scraped away
  3. The joints are cleaned and any rotten wood is routed out
  4. Epoxy resin is used to fill any gaps and then new timber is spliced in
  5. The sash is sanded and often primes
  6. The glass is put back into places
  7. The window is finished and painted
  8. Old weatherstrips are replaced, new hardware is attached, new chain or cords are fitted, the pulleys are rebalanced or lubricated, and then the sashes are reinstated in the frames.  

Our estimate: 1–2 days; £250 per sash

Glazing Requirements

Many want to know if they can have new double-glazed units fitted into their existing timber sashes. The advice is to be careful — these windows were never designed to take two panes of glass, each thicker than the original.

The glazing bars in old sash windows are often not deep enough to take sealed double-glazed units, which ultimately leads to premature misting.

Another option is to have new sashes made to fit your existing frames and to match the originals. Ventrolla use new slim glazing units and traditional methods of carpentry for an authentic look.