Old windows let cold air in through the gaps around the moving parts, not through the glass itself. That is the first thing to understand when you ask how to make old windows less draughty, because it changes what you fix. The glass in a sash window is a single thin pane and it does lose heat, but the draught you feel on your neck comes from air slipping through the meeting rail, the parting beads and the gaps where the sash slides in its frame. Seal those gaps and the room feels warmer at the same thermostat setting, often before you spend anything on the glass at all. This guide works through the fixes in order of value, from brush strips that cost little and take an afternoon, to secondary glazing, which Historic England calls the preferred option for older homes.

How to make old windows less draughty: the short answer

How to make old windows less draughty? Fit brush strips on sliding sash windows, seal fixed panes with silicone sealant, and add secondary glazing if you want the biggest single improvement. The Energy Saving Trust is clear that foam strips do not work well on sliding sash windows, so brush strips are the right choice there. Historic England’s tests found that draught-proofing a sash window in good condition can cut the air leaking through it by as much as 86 per cent, and that is air leakage, not your heating bill, but it explains why a sealed sash feels so different. Heavy lined curtains help at night, and repairing loose putty, split beads and broken cords comes before any sealing, because a seal cannot do the job of a repair.

Why old windows feel so cold

A sash window is a moving machine. Two sashes slide past each other in a timber box frame, counterbalanced by weights on cords hidden inside the frame. Every sliding surface needs clearance, and every clearance is a gap for air. Over decades the gaps widen: paint builds up and then cracks, timber shrinks and swells with the seasons, cords stretch, putty dries out and falls away, and the staff bead that holds the inner sash in place works loose. The result is a window that looks shut but leaks like a sieve around its edges.

Casement windows have the same problem in a different shape. A casement closes against its frame, so the seal depends on the frame staying square and the hinges staying true. Old casements sag on their hinges, the latch no longer pulls the sash tight, and the gap along the hinge side grows wider every winter. Metal windows, common in houses built between the wars, rust at the glazing bars and distort, which opens gaps that no strip of foam will close on its own.

The glass itself is a smaller part of the story than most people assume. A single pane loses heat by conduction, and it will always feel cold to the touch, but the cold you feel across the room is moving air. That matters for anyone learning how to make old windows less draughty, because moving air is cheap to stop and glass is expensive to replace. Historic England makes the same point in its guidance for older homes: there is no reason why older windows cannot be as energy efficient as new ones, and repair plus draught-proofing, or secondary glazing, is the recommended route. Replacement is the last resort, for windows that are beyond repair.

Find the draughts before you fix anything

Do not buy anything until you know where the air is coming in. The Energy Saving Trust suggests a simple walk-round, and it needs no kit at all. On a windy day, look for slivers of daylight showing around the frame, listen for rattles and whistling, and feel for moving air with the back of your hand around the meeting rail where the two sashes cross, along the sides where the sashes slide, and at the corners of the frame. If your curtains stir when every window is shut, you have a draught.

Check each window separately and note what you find. A sash that rattles in its frame needs brush strips and probably a new staff bead. A sash that sticks needs the paint build-up eased before anything is sealed, because a strip that is crushed by a tight sash will not last a season. A fixed pane with cracked putty needs re-puttying, not a strip. A casement that will not pull tight needs its hinges and latch looked at first. Ten minutes of checking saves you from sealing the wrong gap, and it tells you whether one window is the problem or the whole house needs attention. It is the first step in how to make old windows less draughty, and it costs nothing.

While you are checking, look at the ventilation too. Trickle vents in the frame, air bricks in the wall and vents for gas appliances are there for a reason, and they must stay open. The Energy Saving Trust warns that you should not block fixed ventilation openings needed for flueless or open-flue gas heaters, and that a home that is already fairly well draught-proofed may not need more sealing. Draughts are uncontrolled air; ventilation is controlled air. The job is to remove the first without removing the second.

1. Fit brush strips on sliding sash windows

Brush strips are the single most effective fix for a sliding sash, and they are the one the Energy Saving Trust recommends by name. Foam strips are cheap and easy to stick on, but they do not work well on sliding sashes: the sliding movement crushes them, they lose their spring, and within a season the gap is back. Brush strips, or metal or plastic strips with wipers attached, last longer and keep working as the sash moves.

A brush strip kit for a sash window usually covers three places. The parting bead is the thin vertical strip between the two sashes, and it takes a brush on each side. The staff bead is the inner strip that holds the lower sash in place, and it takes a brush along its edge. The meeting rail, where the top of the lower sash meets the bottom of the upper sash, takes a brush or a wiper strip. Fit all three and you have sealed the whole sliding path. Fit only one and the air simply finds the next gap.

The work is straightforward DIY if the sashes are in reasonable condition. Remove the staff bead, ease the lower sash out, fit the brush carrier into a groove or stick the self-adhesive carrier to the bead, and refit everything. Measure the gap before you buy, because the Energy Saving Trust warns that a strip that is too big will get crushed and stop the window closing, while a strip that is too small leaves a gap. If the sashes are badly worn, swollen or out of square, this is the point to call a professional rather than force a strip into a gap it cannot fill. The Energy Saving Trust advises getting three quotes from reputable installers, and TrustMark, the government-endorsed quality scheme, keeps a list of certified draught-proofing installers.

2. Seal the windows that never open

Some windows in an old house never open. A fixed light above a door, a small pane in a stairwell, a window painted shut decades ago: these do not need a moving seal, they need a permanent one. For windows that do not open, the Energy Saving Trust recommends silicone sealant, applied along the joint between the glass and the frame and between the frame and the wall.

Before you seal, check the putty. Old linseed oil putty dries, shrinks and cracks, and once it has cracked it no longer holds the glass tight. Dig out the loose putty, prime the rebate if it is bare timber, and bed in new putty with a putty knife. It is slow, old-fashioned work, and it is also the correct repair: a bead of sealant over failed putty is a patch, not a fix, and it will fail at the same place.

Do not seal a window shut that you need for ventilation or as a fire escape route. A bedroom window that is your second way out in a fire must stay openable. If a window has been painted shut and you want it working again, a sharp knife along the paint line and a gentle easing with a putty knife will usually free it, though a sash that has been shut for years may need its cords checked once it moves.

3. Add secondary glazing for the biggest single gain

Secondary glazing is a second pane fitted on the inside of your existing window, and it is the biggest single improvement you can make to an old window without replacing it. Historic England’s research found that secondary glazing can reduce heat loss by over 60 per cent, and in some situations it can bring even greater energy efficiency improvements than double glazing. It is also the option Historic England recommends for older homes, ahead of replacement double glazing, because it keeps the original window and its character intact.

The reason it works so well is the gap. A secondary pane set 50 to 200 millimetres inside the original creates a layer of still air, and still air is a good insulator. That gap also cuts noise, which is why secondary glazing is popular on busy roads. The units come in several forms: fixed panels for windows you never open, hinged panels that swing in for cleaning, and vertical sliding panels that mirror a sash window so you can still open it for ventilation.

There is one rule that catches people out. Historic England warns that where you install secondary glazing, you should prevent condensation and mould developing by not draught-proofing the original window. That sounds backwards, but the logic is sound: the cavity between the two panes needs a little air movement so moisture can escape. If you seal the outer window tight and the inner pane tight, moisture gets trapped between them and condenses on the cold outer glass. Seal the secondary pane well, leave the original window able to breathe, and the cavity stays dry. Our guide to secondary glazing costs breaks down the prices by type, so you can compare a DIY magnetic kit with a professionally fitted system before you commit.

4. Try window film for a cheap winter fix

Window film is the cheapest way to add a second layer to an old window, and it is a good stopgap while you decide on secondary glazing. A shrink film kit is a sheet of clear plastic film, double-sided tape and a hairdryer. You tape the film to the frame, warm it with the dryer, and it shrinks drum-tight across the pane, trapping a layer of still air between the film and the glass.

It is not as good as glass secondary glazing, and it is not permanent: the film lasts a season, it can tear if it is knocked, and it looks less good than a proper panel. But it costs little, it needs no tools beyond a hairdryer, and it takes the edge off the coldest glass in the house. It works best on windows you rarely open, because every time you peel the film back to open the window you break the seal. Use it on the spare bedroom, the stairwell and the windows behind furniture, and save the proper secondary glazing for the rooms you live in.

5. Hang heavy curtains, blinds or shutters

What you hang at the window matters as much as what you seal. Historic England’s research into making windows more energy efficient found that you can significantly reduce heat loss with window shutters, insulated blinds or thick curtains, and it recommends closing shutters at night. The principle is the same as secondary glazing: a layer of still air between the room and the cold glass.

For curtains to work, they need to fit. Heavy lined curtains that hang close to the frame, reach the sill or the floor, and close fully across the window will do far more than a thin pair that stops short and gapes at the sides. A pelmet above the curtain rail stops warm air falling behind the curtain and sliding down the cold glass, which is the leak most people miss. If your house still has its original shutters, use them: close them at dusk and you have a solid insulating layer that costs nothing.

One mistake to avoid is letting long curtains hang over a radiator. The radiator heats the air behind the curtain, the warm air rises behind the fabric and falls down the cold glass, and the room stays cold while the window gets all the heat. Tuck curtains behind the radiator, or choose sill-length curtains for windows with radiators beneath them, so the heat reaches the room.

6. Repair the window before you seal it

Sealing is not a substitute for repair. Repair is part of how to make old windows less draughty, not a detour from it. A brush strip will not hold in a staff bead that is split, a wiper strip will not seal a sash that has dropped on a broken cord, and no amount of sealant will save a frame with rot at the sill. Before you spend anything on draught-proofing, fix what is broken.

Most sash window repairs are within reach of a competent joiner and some are simple DIY. Broken cords can be replaced, though it means opening the weight pocket and rehanging the sash. Split beads can be replaced with new timber. Rot at the sill can be cut out and spliced, which is cheaper and less disruptive than replacing the whole frame. A sash that sticks can usually be eased by removing paint build-up from the sliding surfaces and waxing them.

The case for repair is strong on its own terms. Historic England notes that properly maintained historic timber windows can last indefinitely, because they were made from durable timber by craftsmen, and that repairs usually cost less than replacement, preserve the character of the house, and will not usually need consent. A uPVC replacement window, by contrast, has a service life of under 25 years, while a well-maintained traditional window can survive for over 100 years. Double or triple glazed units need replacing roughly every 30 years, against 60 to 100 years for a single glazed window. Repairing the window you have is usually the cheapest option and the longest-lasting one.

What about listed buildings and conservation areas?

If your house is listed or in a conservation area, the rules are different, but draught-proofing is still the easiest win. Historic England’s position is that draught-proofing provides the biggest energy saving and conservation benefits for the lowest environmental and financial costs, and it is where every listed building project should start.

Simple self-adhesive draught-proofing strips do not require listed building consent. Like-for-like repairs will not usually need consent either. More invasive methods, such as cutting grooves into the frame to house a brush carrier, may affect the special interest of the building and may require consent, so ask first. Reversible secondary glazing does not generally need listed building consent, and consent would only be needed if installation damaged the frame, panelling, shutters or other historic features. Always check with your local authority’s conservation officer before work begins, because every listed building is a separate case, and unauthorised alterations to a listed building are a criminal offence.

If you do want better glass, slim-profile or vacuum double glazing units can sometimes be fitted into historic frames. Historic England says this will generally be acceptable where the frames of special interest are kept, no important historic glass remains, and the extra weight can be accommodated. It is a specialist job, and it needs consent, but it is an option worth knowing about before anyone suggests replacing the windows outright.

What not to block

Draught-proofing is about removing uncontrolled air, not about sealing the house shut. Some gaps are doing a job, and blocking them creates a worse problem than the draught.

Never block trickle vents, wall vents or air bricks. These are controlled ventilation, and they keep fresh air moving through the house. Never block the fixed ventilation openings needed for flueless or open-flue gas heaters: those appliances need air to burn safely, and blocking their ventilation is dangerous. Do not draught-proof internal doors. The Energy Saving Trust is explicit on this: there should be a gap beneath internal doors so air can move around the house, and sealing them can trap moisture in closed rooms.

Be careful in rooms where a lot of moisture is produced, such as kitchens, bathrooms and utility rooms. These rooms need ventilation more than they need sealing, and over-sealing them raises the risk of condensation and mould. If a room already has a condensation problem, fix the ventilation first and draught-proof second. Our guide to stopping window condensation explains the balance in detail, and it is worth reading before you seal a bathroom or kitchen window.

The same logic applies to the whole house. The Energy Saving Trust warns that if your home is already fairly well draught-proofed, adding more may increase the risk of poor air quality. Draught-proof the windows and doors, leave the vents alone, and let the house breathe in the places designed for it.

What it costs and what it saves

Professional draught-proofing of windows and doors costs around £250 for a whole house, according to the Energy Saving Trust, and DIY work is cheaper. The saving from draught-proofing windows, floors and doors is around £55 a year in Great Britain, or £80 in Northern Ireland, and draught-proofing an unused chimney adds around £45 a year in Great Britain. Those are modest numbers, and they are honest ones: draught-proofing will not halve your heating bill.

The real return is comfort. A draught-free room feels warmer at the same thermostat setting, so you can turn the heating down. The Energy Saving Trust puts a number on that too: turning the thermostat down from 22 degrees to 21 degrees can save £120 a year in Great Britain, and £80 in Northern Ireland. A room without a cold draught across the sofa is a room you are happy to sit in at 20 degrees, and that is where the saving actually comes from.

Think of how to make old windows less draughty as a sequence rather than a single purchase. Start with brush strips on the sashes and sealant on the fixed panes, which is a weekend of work and a small spend. Add heavy curtains before the coldest weeks. If the windows are still cold, price secondary glazing for the worst rooms first, and repair anything broken before you seal it. Old windows do not need replacing to stop being draughty. They need their gaps closed, their repairs done, and a second layer where it counts.

Frequently asked questions

How do I stop draughts from old sash windows?

How to make old windows less draughty starts with the sashes. Fit brush strips along the parting bead, the staff bead and the meeting rail, and repair split beads and broken cords first. Foam strips do not work well on sliding sash windows because the sliding movement crushes them, so use brush strips or wiper strips, or hire a professional. Historic England’s tests found draught-proofing a sash in good condition can cut the air leaking through it by as much as 86 per cent.

Can I draught-proof windows in a listed building?

Yes. Simple self-adhesive draught-proofing strips do not require listed building consent, and like-for-like repairs will not usually need consent either. More invasive methods, such as cutting grooves into the frame, may require consent. Reversible secondary glazing does not generally need consent unless it damages the frame, panelling or shutters. Always check with your local authority’s conservation officer before work begins.

Is secondary glazing better than double glazing for old windows?

For an old window, usually yes. Historic England’s research found secondary glazing can reduce heat loss by over 60 per cent, and in some situations it can bring even greater energy efficiency improvements than double glazing. It keeps the original window, it is reversible, and it does not generally need listed building consent. Replacement double glazing changes the frame, the glazing bars and the appearance, and it needs consent in a listed building.

Does window film really stop draughts?

Window film helps, but it does not stop draughts on its own. Shrink film taped to the frame and tightened with a hairdryer traps a layer of still air against the glass, which cuts heat loss through the pane. It does not seal the gaps around the sash, so fit brush strips as well. Film is a cheap seasonal fix for windows you rarely open, not a replacement for proper draught-proofing or secondary glazing.

Should I draught-proof the original window if I fit secondary glazing?

No. Historic England warns that where you install secondary glazing, you should prevent condensation and mould developing by not draught-proofing the original window. The cavity between the two panes needs a little air movement so moisture can escape. Seal the secondary pane well and leave the original window able to breathe, and the cavity stays dry.

How much does it cost to draught-proof old windows?

Professional draught-proofing of windows and doors costs around £250 for a whole house, according to the Energy Saving Trust, and DIY work with brush strips and sealant is cheaper. The saving from draught-proofing windows, floors and doors is around £55 a year in Great Britain, or £80 in Northern Ireland. The bigger saving comes from comfort: a draught-free room feels warm at a lower thermostat setting, and turning the thermostat down by one degree can save £120 a year in Great Britain.

Related reading

If you are weighing up secondary glazing, our guide to secondary glazing costs in the UK breaks down the prices by type. For the wider job, our guide to stopping draughts around windows and doors covers the cheap seals to fit before winter. And if your house is a century old, our guide to insulating a 100 year old house puts the windows in the context of the whole building.

Sources

Energy Saving Trust, draught-proofing guide: professional draught-proofing costs, savings figures, sash window brush strip advice, and what not to block. https://energysavingtrust.org.uk/advice/draught-proofing/

Historic England, repair or change windows in an older home: repair before replacement, secondary glazing heat loss reduction, condensation advice, and the service life of traditional windows against uPVC. https://historicengland.org.uk/advice/your-home/maintain-repair/windows/

Historic England, modifying historic windows as part of retrofitting energy saving measures: draught-proofing as the biggest energy saving for the lowest cost, listed building consent rules for strips, grooving and secondary glazing. https://historicengland.org.uk/advice/technical-advice/retrofit-and-energy-efficiency-in-historic-buildings/modifying-windows-and-doors-in-historic-buildings/modifying-historic-windows-as-part-of-retrofitting-energy-saving-measures/