A sash window needs a quick check twice a year and a proper service every few years. Clean the runners, inspect the paint and putty, test the cords and prod the sill for soft timber. Small faults are cheap to fix early, because left alone, they let water in and the repair bill grows.
Why maintenance matters for timber sashes
Timber windows do not fail overnight. Instead, a flaking patch of paint lets rain reach bare wood, the wood swells, and the sash starts to stick. Then the cords fray under the extra strain. One neglected corner can lead to three separate repairs.
Councils say the same thing. Lewisham Council’s guidance on historic windows notes that timber windows typically need repainting every three to five years, depending on which way they face and how well they were painted before. The same guidance points out that rotten parts can often be cut out and renewed at a fraction of the cost of a whole new window.
So a little regular attention protects the original timber. In London, that timber is often old, dense and slow grown. As a result, it is usually worth keeping.
Spring: the main inspection
Spring is the best time for a full look, because the winter damp has shown you where the weak spots are. Start outside and work inwards.
First, check the paint on the bottom rail, the sill and the joints where the frame meets the brickwork. These areas hold water longest, so they fail first. Look for cracks, bubbling and bare patches.
Then press a thumbnail or a screwdriver tip gently into the sill. Sound timber resists, while rotten timber crumbles or feels spongy.
Next, look at the glazing putty around each pane. Putty should be firm and sealed against both the glass and the timber. However, if it is cracked or has fallen away, water can reach the rebate behind it. Small gaps can be patched, but widespread failure means the glass needs re-puttying.
Finally, open and close each sash. It should move smoothly and stay where you leave it, since a sash that drifts has a fault. A sash that drops by itself usually has a broken cord, which a sash cord replacement deals with directly.
Summer: paint and repair weather
Dry weather is the right moment for decorating and repairs. Paint will not cure properly in damp or cold conditions. Therefore, schedule the work for the warmest, driest weeks.
First comes preparation. Sand off loose and flaking paint and fill small cracks. Then apply primer to any bare timber before the undercoat. Bare wood painted with undercoat alone fails early, because the paint cannot grip.
However, take care not to paint the sashes shut. Paint in the runners and across the meeting rails is the usual cause of windows that will not open. Our guide to painted-shut sash windows explains how to free them safely and how to avoid the problem next time.
Also use the summer to book any larger repairs. Autumn can be a busy time for joiners, so booking early helps. A full sash window overhaul in summer means the windows are ready before the cold arrives. Our costs page shows that an overhaul with draught proofing is priced at £188 per window.
Autumn: seal against the cold
Autumn is for draughts. Before you turn the heating on, check where air is coming in, because that is when leaks show.
On a windy day, hold the back of your hand near the meeting rail and the edges of each sash. You will feel moving air if the seals have failed. You may also hear a rattle. However, a rattle alone usually means the sashes have loosened in the frame.
Our post on why sash windows rattle covers the causes in detail. A rattle has several possible sources, so it helps to know them.
Brush-pile seals fitted into the frame can cut draughts without changing how the window looks. That is the core of sash window draught proofing. Because the seals sit out of sight, they also suit period homes where appearance matters.
If your main concern is heat loss through the glass, think about what the window can carry. For example, some homeowners ask about slim double glazing. Our comparison of slim double glazing and vacuum glazing explains what each option involves and what the original sashes can support.
Winter: watch for moisture
In winter, the job is observation, since you can see faults clearly. Watch for condensation on the inside of the glass, damp patches on the sill and water pooling at the bottom of the sash.
A little morning condensation is normal on single glazing in a cold room. Heavy, constant moisture is different, because it can stain the sill and push paint off the timber. We will cover causes and remedies in our guide to condensation on sash windows.
In the meantime, wipe the sill dry, keep trickle vents or an extractor working in kitchens and bathrooms, and avoid drying laundry next to the window. Do not seal the window with plastic film for long periods, because that traps moisture against the timber.
A simple twice-a-year checklist
Use the same routine each spring and autumn. First, clean the glass and wipe the sills and runners. Then check the paint on the bottom rails and press the sills for soft spots, because rot starts there.
Next, test that every sash opens, closes and stays put. Also look for gaps in the putty and check that locks and catches still engage. Because each step takes seconds, the whole house goes quickly.
For the runners, brush dust and grit out of the runners with a soft brush. Then rub a little candle wax or dry lubricant on the runners. Avoid oil because it attracts dirt. Do not use paint or silicone sprays inside the track.
Local conditions across London
London brings its own pressures. Traffic grime, damp basement flats and exposed top-floor windows all age timber faster. For example, a Victorian terrace with box sashes in sash window repairs in Wandsworth faces much the same wear as a Georgian townhouse among sash windows across Camden, even though the glazing bars differ.
However, aspect matters. A sheltered, north-facing front may hold damp for longer, so it may need paint more often. South-facing windows suffer more from sun and may dry out and crack at the joints. Terraces in homes across Hackney often show both patterns on the front and back of the same house.
When to stop and call a specialist
Some jobs are beyond routine care. Call a specialist when a sash will not move at all, even after careful freeing. However, the same goes for a snapped cord or a sash that drops.
Also call one if the sill or bottom rail feels soft over a wide area. Loose glass and visible daylight around the sash are further warning signs, because both mean the window is no longer sealed.
Conservation areas add another consideration. If your home is in one, check what you may change before replacing anything. For example, our guide to sash windows in London conservation areas explains the rules.
Sometimes the windows are past routine care. In that case, our guide on whether to repair or replace sash windows sets out how to decide. Most original sashes can be saved, so a specialist visit is usually about repair, not replacement.
Next steps
Start with a walk around the house this weekend. Note what needs attention and photograph anything that worries you. Then request a free site visit and written quote through our contact page. We cover all Greater London postcodes, and our work carries a five-year guarantee on labour and the draught-proofing system.