Repair is the right answer for most sash windows, because the timber is usually sound and the faults are small. Replace only when the frame is rotten through, the sashes are beyond saving or the design is wrong. Check the condition first, then compare costs and the effect on your home.
Start with the condition, not the price
Many people ask for a quote to replace their windows. They often mean they want the draughts and the sticking to stop. A repair can do that, so it pays to find out what is really wrong.
Walk round the house and look at each window. Open it, close it and press the timber.
Note anything that sticks, rattles, leaks or hangs open. Then sort the faults into two piles. In the first are fixable faults. In the second are signs the window has failed.
Our guide to the signs your sash windows need repair lists the common ones. In short, most are repair jobs.
Faults that point to repair
Most sash faults are small, because the design is simple. A sash is a timber frame holding glass, and each part can be mended on its own.
A broken cord is the classic example. It stops the window staying open, yet the fix is cheap. Our guide to broken sash cord replacement explains the job. Likewise, a stuck sash, a loose joint, a cracked pane and a worn catch are all routine repairs.
Rot is the fault people fear most. However, it is often local. A soft patch on the sill or the bottom rail can be cut out and a new piece of timber spliced in. Lewisham Council’s guidance on historic windows says that even where parts have rotted, these parts can often be cut out and renewed at a fraction of the cost of replacing a whole window.
A rotten patch is not a reason to scrap the window, because most rot is local. Check how far it spreads before you decide.
Faults that point to replacement
Some windows are past saving. That is rare, but it still happens.
First, widespread rot. If the sill, the frame and both sashes are soft, a repair will cost close to a replacement.
Next, damage from a past bad repair. Some windows have been cut down or fitted with the wrong glass, and putting them right can cost more than starting again.
Finally, a window may never have been a good design. Some 20th-century replacements copy the sash look but not the build. They may be a poor fit, so a repair may not be worth it.
Even then, you rarely need a whole new frame, since often only the sashes are replaced. Our replacement sashes service makes new sashes to match your original frame, so the window looks the same.
Cost: compare like with like
Here is where the numbers help, because our price list shows what each route costs.
An overhaul with draught proofing is £188 per window. A sill replacement is £120 per window, and a bottom-rail repair is £120. A small splice repair is £80. A replacement sash is £190, though ornate or multi-bar sashes cost more.
By contrast, double glazing an existing sash is £480. A new double-glazed sash in the original frame is £680, and a full double-glazed replacement is £1,480. Those figures show why repair usually wins on cost alone.
Our guide to sash window repair costs in London explains what drives each price. The costs page lists every figure.
Lifespan: old timber lasts
Age is not a fault, although it is easy to assume so. Lewisham Council’s guidance points out that original windows might be 100 or more years old and, when overhauled and repaired, will be able to last a lot longer. It adds that 19th-century timber was grown slowly, so it is very dense. Such quality can rarely be matched by the timber available today.
That does not mean old windows last forever. They need care, and paint is the first line of defence. The same guidance says that all windows need regular upkeep, so new windows will need attention too.
Therefore, think about the cost of owning a window, not just buying it. A repaired original can last for decades. A cheap replacement can fail much sooner.
Energy: the draught is the problem
Many owners replace windows to save energy. Yet gaps around the sash matter as much as the glass, and gaps are cheap to fix.
So fix the gaps first. Our sash window repairs work includes easing, rehanging and sealing sashes so they close properly. Brush seals then cut the draughts without changing how the window looks.
If you want more, you can still add glazing. Our comparison of draught proofing and secondary glazing explains what each option adds. Noise is another reason people want to change windows, and we will cover that in our upcoming guide to reducing traffic noise through sash windows.
Heritage: the look of the street
Sash windows are part of what makes a London street look the way it does. Since that look matters, councils care what happens to them.
In a conservation area, you may need consent to change a window’s appearance. Wandsworth Council, for example, asks residents to retain and repair existing original timber windows wherever possible.
If your home is listed, the rules are stricter still. Our guide to double glazing listed sash windows explains how consent works in that case. Repair is almost always the easiest route, because it keeps the original.
A simple way to decide
Use four questions because each one narrows the choice. First, is the frame sound? If it is, repair.
Second, is the damage local? If it is, splice or replace the part.
Third, would the repair cost more than half of a replacement? If it would, compare quotes. Fourth, does your home have heritage value or sit in a controlled area? If so, lean towards repair.
This is only a guide, because every window is different. A site visit is the best way to find out, since we look at the timber, the cords, the glass and the fit, and then tell you what we would do.
Repair or replace across London
London homes vary a great deal, so the answer varies too. Victorian terraces among sash window repairs in Wandsworth often have sound original sashes that respond well to an overhaul. By contrast, flats that were converted long ago may carry a mix of old and new windows.
In homes across Lambeth, you may find terraces where only the front sashes are original. Meanwhile, larger period houses among sash windows across Richmond upon Thames often sit in conservation areas, so repair is usually the safer route.
Next steps
If you cannot decide, book a survey, because a clear answer saves money. We offer a free site visit and a written quote through our contact page. We will say plainly if a window needs replacing, and if it does not, we will say that too. Our work carries a five-year guarantee on labour.