Why older windows are draughtier than they look

Older windows are one of the joys of a period property, but they can also be one of its chilliest features. A sash window that rattles in the wind or a frame with a hairline gap might not seem like much, yet those small openings add up. Cold air sneaks in, warm air escapes, and your heating bill quietly climbs. The good news is that most draughts around older windows can be reduced substantially with a few well-chosen materials and a patient afternoon. The trick is to work gently, so you keep the original character that makes your home special.

Draughts in older windows usually come from three places: the gaps between the moving sashes and the frame, the meeting rails where the top and bottom sashes overlap, and the perimeter where the frame meets the wall or the opening casement. Timber also shrinks and swells with the seasons, so a gap that seems minor in summer can become a noticeable leak by January. Before you buy anything, spend ten minutes on a windy day with a damp hand or a thin tissue to find where the air is actually coming in. That simple check saves you from sealing the wrong spots.

Brush seals: the quiet hero of sash window draught-proofing

For traditional sash windows, brush seals are often the best first step. They consist of a flexible carrier strip with dense bristles that press against the moving sash without stopping it from sliding. Unlike foam tape, which can jam a sash or peel away, brush seals are designed for sliding surfaces and can last for years. You can fit them to the staff beads, the parting beads, or the frame itself, depending on where your gaps are.

Fitting brush seals is fiddly but satisfying. Start by cleaning the surfaces with a dry brush and a slightly damp cloth, then let them dry fully. Measure twice, cut the seal with sharp scissors, and test the sash movement before committing to a full length. If the sash becomes stiff, a thinner brush or a different carrier profile may be needed. A little silicone spray on the brush can help it glide, but avoid oil-based products that might stain bare timber.

• Side gaps: fit brush seals to the staff beads or the sash stiles.
• Meeting rails: use a brush seal or a flexible fin seal where the sashes overlap.
• Top and bottom: check the head and sill for gaps that a brush strip can close.

Draught excluders for frames, sashes and casements

Not every gap suits a brush seal. For casement windows, compression seals — often made from rubber or silicone — work well because the window closes against them. Self-adhesive foam strips are cheap and easy, but they compress over time and can leave a sticky residue on historic paintwork. If you use them, choose a low-tack version and test on a hidden area first. For awkward spots, a simple fabric draught excluder or a weighted door snake can be surprisingly effective, especially at the bottom of a sash where the sill has worn.

Adjusting the window hardware can also make a difference. Sash windows have a system of weights, cords and pulleys; if the sashes are loose, they may not close tightly. A sash that rattles can sometimes be quietened by tightening the staff bead screws or adding a thin shim behind the bead. For casements, check the hinges and the locking handle. A handle that no longer pulls the window firmly against the frame can often be adjusted with a screwdriver rather than replaced.

Filling gaps without harming original features

When you need to fill a gap around a frame, resist the temptation to reach for cement or a rigid filler. Historic timber moves, and a hard filler will crack or pull away, taking paint and possibly original mouldings with it. Instead, use a flexible decorator's caulk or an acrylic sealant that remains slightly elastic. For deeper gaps, push in a foam backer rod first, then apply the sealant over the top. This gives the filler something to sit against and reduces the amount you need.

If the gap is between the frame and the wall, and the plaster is sound, a bead of caulk can be smoothed with a damp finger. For painted timber frames, use a sealant that can be overpainted. Avoid silicone in areas you plan to paint, as paint will not stick to it. For small cracks in the timber itself, a flexible wood filler is fine, but keep it shallow. If the timber is rotten, stop and treat the cause before sealing anything. Trapping moisture behind a repair will only make things worse.

Seasonal checks and a few things to avoid

Draught-proofing is not a one-off job. Before winter, run a quick check: look for new gaps, test that sashes still slide, and make sure seals have not perished or come loose. Spring is a good time to clean and lubricate moving parts, while autumn is ideal for topping up any worn seals. A little maintenance keeps the whole system working.

• Avoid over-sealing: older windows need some ventilation to prevent condensation and rot.
• Do not block trickle vents or air bricks, even if they feel draughty.
• Skip expanding foam around historic frames; it can bow timber and is hard to control.
• Test before you commit: always check that a window still opens and closes freely after fitting any seal.

When to stop and rethink

If a window is severely warped, has rotten sections, or lets in water as well as air, draught-proofing alone will not solve the problem. At that point, it is worth speaking to a joiner who understands period properties. They can repair or replace damaged sections while preserving the original look. For many older homes, the most effective long-term improvement is a combination of careful draught-proofing, good curtains, and secondary glazing that can be removed in summer. But even the simplest brush seal and a tube of flexible filler can make a room feel noticeably warmer. Start with the worst gap, work methodically, and you will be surprised at how much comfort you can restore without losing the character of your windows.