Draught Proofing a Sash Window Yourself

We fit draught proofing for a living, so take this page for what it is — but there is no sense pretending that every draughty window needs a tradesman. Some of the DIY options are genuinely good value, one or two are better value than anything we could sell you, and a couple of the popular ones are a waste of an afternoon. Here is the honest version.

The short answer: you can do a lot to the parts of the window that do not slide, and very little to the parts that do. That single distinction explains almost everything below.

Start by finding out where the draught actually is

Before buying anything, find the leak. On a cold, windy day, run the back of a damp hand slowly around the window — down the sides of the bottom sash, along the meeting rails where the two sashes cross, along the bottom rail, along the top of the upper sash, and around the outside of the frame where it meets the wall. A lit incense stick or a thin strip of tissue held near the joint shows the movement more clearly.

People are frequently surprised by the result. A good share of what gets blamed on the window turns out to be the gap between the frame and the masonry, or the floorboards under the window, or an unused chimney in the same room. Those are cheap to fix and have nothing to do with the sashes.

The DIY options, ranked honestly

1. Sealing the frame to the wall — the best DIY job there is

The junction between the timber box frame and the masonry opens up as old mortar perishes, and on a London terrace it is very often the real source of the draught. A tube of decorator's caulk or a flexible frame sealant, a caulking gun and an hour gets you a continuous seal around the frame, inside and out. It is cheap, it needs no skill beyond a steady hand and a wet finger, it is invisible once painted, and it cannot make the window stiff because nothing moving is involved.

If you do one thing on this page, do this one. Use a flexible sealant rather than filler, which cracks as the building moves.

2. A meeting rail fastener that actually works

The fastener where the two sashes cross is not just a lock. Its job is to pull the two meeting rails tightly together and lift the bottom sash slightly into its rebate. A worn, loose or missing fastener leaves a slot straight across the width of the window, and that slot is often the single biggest hole in a sash window.

Tightening the screws on a loose one, or fitting a new brass fastener, is a screwdriver job. It costs very little and it is the highest-value ten minutes you can spend on a sash window. Do this before you buy any strip at all.

3. Secondary glazing panels — the best DIY result, at a price (but do not do both)

Magnetic or clip-in secondary glazing is a clear acrylic panel held in a slim frame fixed to the window reveal. It is the one DIY option that addresses the glass as well as the gaps, so it does noticeably more than any strip: warmer, and a real difference to street noise.

It is a measuring-and-cutting job rather than a skilled one, and kits are sold cut to your dimensions. The catches are cost — it is the most expensive thing on this list — and that the panel has to come off to open the window, which is fine for a bedroom in winter and irritating in a kitchen.

Important: pick one or the other. Historic England advise that where secondary glazing is installed, the original window should not also be draught proofed — sealing both traps moisture in the cavity between them and you end up with condensation on the inside face of the original glass, where it is awkward to reach. Secondary glazing is generally the better choice for noise; draught proofing is the better choice if you want to keep using the window normally.

4. Self-adhesive brush pile strip

This is the DIY version of what we fit, and it is the only stick-on product that suits a surface which slides past it. Applied to the staff bead where the bottom sash runs, and to the parting bead, it closes a real part of the gap without seizing the window.

The limitation is the adhesive. Our seal sits in a routed groove and is held mechanically; a stick-on strip is held by tape, on old paint, in a place that gets rubbed by a moving sash every time the window is opened. It lifts, eventually. Expect a season or two of good service rather than decades, and expect to be picking adhesive residue off the paintwork afterwards.

5. Foam and rubber self-adhesive strip — use it in the right place only

The cheap foam tape sold in every DIY shop is designed for a hinged door or casement, which closes onto the seal and compresses it. A sash window does not do that: the sash slides past the seal. Put foam strip in the sliding runs and one of two things happens — either the sash will not move, or the strip is shredded and hanging off within weeks.

Where it does work is anywhere the two surfaces meet rather than slide: along the top of the upper sash, under the bottom rail, and on the meeting rail. Used there, on those three surfaces only, a good quality EPDM rubber profile is decent value and lasts far longer than foam. Buy it by the gap, not by the name: E profile seals 1.5–3 mm, P profile 3–5 mm and D profile 3–6 mm. Measure first — a profile that is too fat will stop the window closing.

6. Sealing a window you never open

If a particular sash is never opened — a top sash that has been painted shut for forty years, a window in a room with another opening light — you can simply seal it. A bead of flexible sealant around the closed sash, or a strip of low-tack seasonal tape, and the draught is gone entirely. This costs almost nothing and works better than any product designed to seal a window that still has to move.

Two cautions: do not seal the only opening window in a room, and do not seal a window that is an escape route from a bedroom.

7. Blocking the pulley slots

The slots the sash cords run through open straight into the weight cavity inside the wall. Small brush-type pulley covers are sold for a few pounds and close the hole while letting the cord move. A minor gain, but a cheap and easy one.

Do not stuff the slots with anything solid: the cord has to run, and blocking a working pulley is how a cord gets chafed through.

8. Heavy curtains, a pelmet, and blinds

Frequently dismissed, and it should not be. Interlined curtains that reach the floor, with a pelmet or a closed track at the top so air cannot circulate behind them, make a real difference to how cold a room feels — both by slowing the draught and by putting a layer between you and a cold pane. It is not draught proofing in the technical sense, but the room is warmer, which is what you were after.

The pelmet matters more than people think: without it, the curtain works as a chimney, drawing cold air down off the glass and out along the floor.

9. Shrink-film secondary glazing

Clear film taped to the reveal and shrunk tight with a hairdryer. It is cheap and it does work — it creates a still air gap in front of the glass. But it is a seasonal measure, it looks like what it is, the window cannot be opened while it is up, and the tape can pull paint off an old reveal when it comes down. Reasonable for a spare room or a rented flat, not a solution for the front of the house.

10. Draught snakes and sausages

A fabric tube on the sill. It blocks nothing at all — the air comes in around the sash, not along the flat sill — and it is on the wrong side of the leak. Fine on a badly-fitting external door; on a sash window it is decoration.

What the materials actually cost

Retail prices from the usual UK merchants, current at July 2026. The point of this table is the third column: nearly every product is sold for a specific gap range, and buying the wrong one is the commonest reason DIY draught proofing fails.

Put next to the professional prices — broadly £250–£600 a window with the sashes out and the cords renewed — the arithmetic is honest enough: you can materially improve a draughty sash window for £20 to £30 of materials and an afternoon. What you cannot do for that money is make it permanent, or fix a window whose cords have gone.

What DIY cannot do

Everything on the list above works on the window as it stands. What it cannot do is change the window's condition, and that is what limits it:

• It cannot close the parting bead run properly. Getting a durable seal along the runs where the sashes actually slide means routing the sash edges and fitting a new sealed parting bead — which means taking both sashes out.
• It cannot fix a dropped top sash. If the gap at the meeting rail exists because the top sash has sunk on broken cords, no strip will close it. It needs re-cording.
• It cannot deal with a gap that is simply too wide. Where shrinkage has opened things up beyond a few millimetres, stick-on strip either does not reach or jams the window.
• It does not survive a repaint. Anything stuck to the beads has to come off before painting and go back on afterwards.

Things to be careful about

• Do not paint the window shut. The single most common piece of self-inflicted damage. If you paint a sash window, run a blade round the seal and slide the sashes before the paint cures.
• Assume old paint contains lead. Lead pigments were widely used in UK paint until the 1960s and were not out of common paints until the early 1980s; the sale of lead paint was not prohibited here until February 1992. Historic England's advice is that if there is any doubt on a window you are about to strip, assume lead is present. HSE's practical rules are worth following even as a homeowner: only strip paint back if it is flaking or a risk to children; do not dry-sand it — use chemical stripper, wet abrasive paper or on-tool extraction; keep hot air guns and infrared below 500°C and never use a blow lamp or gas torch; clear debris with a damp cloth and bag it; wear disposable overalls and an FFP3 mask; and keep children and pregnant women out of the work area. See HSE CIS79. (Contrary to what you will read, heat guns are not banned — it is the temperature and the naked flame that matter.)
• Do not force a stuck sash — and this one is not just about the window. Heaving on a painted-shut sash is how glass gets broken, glazing bars get snapped and cords get pulled out of their grooves. More seriously, Historic England warn that a window stuck firmly in place may have taken on a structural role and be carrying the weight of the wall above: they record cases of part of a wall collapsing when such a window was opened. If a sash will not move and there is any cracking, distortion or a gap above the cill, stop and get someone to look at it.
• Take the beads off gently. Original staff beads are worth keeping. Score the paint line first, ease from the middle rather than the ends, and expect them to be fragile.
• Never restrict the air to a fire or a gas appliance. This is the one on the list that actually matters. Historic England advise taking specialist advice before sealing any room containing a gas or oil burning appliance, and the Energy Saving Trust are explicit that fixed ventilation openings serving flueless or open-flue gas heaters must not be blocked. If the room has a working fire, a gas heater or a back boiler, leave the ventilation alone and get advice.
• Do not seal the room airtight. Old houses rely on air movement. Keep the extract fans working and the air bricks clear — otherwise the moisture that used to leave through the gaps ends up as condensation and black mould on the coldest surface in the room. Historic England suggest around 0.4–0.8 air changes an hour for an older building in reasonable condition. The Energy Saving Trust also warn that a home with no trickle vents, wall vents or mechanical ventilation may already be too airtight for further draught proofing to be a good idea.
• Do not draught proof internal doors, roof voids or sub-floor voids. Those spaces are meant to breathe. Sealing a sub-floor void is a good way to create a rot problem under the boards.
• If you already have secondary glazing, do not draught proof the window behind it. Historic England advise against it — sealing both traps moisture in the cavity between them and you get condensation where you cannot easily wipe it.
• Check before you start on a listed building. Reversible, non-damaging measures are usually uncontroversial, but anything fixed to the window or the reveal on a listed property is worth a call to the council's conservation officer first.

A sensible DIY order of work

If you want the most improvement for the least money and risk, do it in this order and stop when the room feels right:

1. Find where the draught is actually coming from.
2. Sort the meeting rail fastener.
3. Seal the frame to the wall, inside and out.
4. Rubber strip on the top rail, bottom rail and meeting rail — the non-sliding surfaces only.
5. Pulley covers if the slots are open.
6. Lined curtains with a pelmet.
7. Then, if the sliding gaps are still the problem, get the sashes out — which is the point at which it stops being a DIY job.

When it is worth calling someone

Call someone when the answer involves the sashes coming out of the frame. In practice that means: cords broken or a sash that will not stay up; a top sash that has dropped; gaps too wide for strip; a window painted so thoroughly shut that freeing it risks the glass; rot in the bottom rail or sill; or simply that you want a seal that will still be there in twenty years and will survive being painted over.

It is also worth pricing the professional job before assuming it is out of reach. Doing several windows in one visit brings the cost per window down a good deal, and because re-cording and draught proofing share the same access, having both done together costs much less than having them done separately. Our costs page sets out what drives the price.