How to draught proof sash windows yourself

The short answer

A sash window leaks air in five places: the top rail against the head of the box, both parting beads, the meeting rails, both staff beads, and the bottom rail onto the cill. Historic England divides seals into compression seals, which work where a part closes against something, and wiper seals, which work where parts slide past each other — and is unambiguous that wiper seals are the only way of sealing the sides and meeting rails of a sliding sash.

That single rule disqualifies most of what is sold in a DIY shed as a "draught excluder" for the parts of the window that leak most. The Energy Saving Trust says the same thing plainly: for sliding sash windows, foam strips do not work well, and it is better to fit brush strips or consult a professional.

How much material one window actually needs

This is where most DIY attempts go wrong before they start. Two independent kit suppliers state the pile quantity per window: one specifies 22 metres for a sash up to 2,950mm × 1,450mm, the other "a total kit of 25 metres of seals" for one up to 2,100mm × 1,050mm.

So budget 20–25 metres of brush pile per window. A 5-metre retail roll does not do one window. Buying trade quantities is dramatically cheaper: a 25m coil of brushpile weatherstrip is around £9–£11 excluding VAT from a sash hardware supplier, which does a whole window and still costs less than two 5m rolls off a shelf.

Pile height — the number most people get wrong

Brush pile is sold by the height of the filament, and it is rated for a specific gap. The published ratings from a major supplier are:

Now cross-reference that with the window. A vertical sliding sash needs roughly a 3mm running clearance to move at all, and on a warped or heavily over-painted window it can be nearer 5mm in places. That puts a typical box sash squarely in the 8.5mm band — not the 5.5mm that most retail rolls supply, and certainly not the 4.5–6mm pile on a general-purpose brush draught excluder.

Get it wrong in either direction and the job fails. Too short and the pile never touches the timber, so it does nothing. Too tall and it binds — the Energy Saving Trust make the same point generically, that an oversized strip gets crushed and you may not be able to close the window. Measure your actual gap before you order anything.

Every DIY option, compared

Prices below were checked in July 2026 and include VAT unless marked otherwise. Trade supplier prices are quoted excluding VAT, as that is how they are listed.

(a) Self-adhesive foam strip

The cheapest thing on the shelf, and the wrong thing for most of this window. Typical products: a two-pack of 7.5m foam weatherstrip for 1–3mm gaps is about £6.19 at the trade counters, the 3–5mm version about £9.99, an extra-thick 2–8mm version about £7.06 for 2 × 3.5m; a 6m self-adhesive draught seal is about £7.00 at the DIY sheds, and a 10m soft foam seal about £8.00 at the DIY sheds. At 20–25m per window that is roughly £15–£25 in materials.

Where it is genuinely correct: the bottom rail where the lower sash closes down onto the cill, and the top rail where the upper sash meets the head of the box. Both are compression joints, and Historic England explicitly permits compression seals there.

Where it fails: everywhere the sash slides. A compression seal on a sliding surface is abraded away a little more every time the window moves, and while it lasts it binds the sash. Stick foam to the face of the staff bead — the single most common DIY mistake — and you foul the sash travel; the window either jams or tears the strip off within a season. Damp foam is also slow to spring back, and it cannot cope with the varying gap widths of 120-year-old joinery.

Lifespan: One retailer's own specification for one common foam strip lists a one-year manufacturer guarantee. Historic England describe foam strips as cheaper still, but with a short life. Difficulty 1/5 — scissors and something to degrease the surface.

(b) EPDM rubber and silicone bulb seals (P, E and V profile)

The same idea as foam but a much better material. A 20m roll of EPDM E-strip (1.5–3mm gaps) or P-strip (3–5mm gaps) is around £14.59 at the trade counters; a 15m P-profile is about £9.10 at the trade counters, with a 100m white roll at about £40.99; a 10m P-profile is around £8.50 at the DIY sheds. Around £10–£20 per window for the compression positions.

EPDM resists weathering, ozone and UV well, and trade sources put its life at around five years — meaningfully better than foam. Historic England note that silicone is taking over from EPDM as the material of choice for compression strips, partly because it comes in more colours including white. The placement rule is identical to foam: correct on the bottom and top rails, wrong on every sliding surface. Difficulty 1/5.

(c) Self-adhesive brush pile — right material, compromised fixing

Now we are using the correct material. Retail: a 10m roll of brush pile with a 6mm filament for 3–5mm gaps is about £8.19 at the trade counters in black, about £12.60 in white; a 5m pile tape is around £7.50 at the DIY sheds. Trade is far cheaper per metre — a 25m coil of brushpile weatherstrip with a fin runs about £8.93 excluding VAT in 5.5mm, £9.98 in 8.5mm and £11.13 in 11.5mm, and 100m coils bring it down to roughly £0.13–£0.18 a metre. A 100m roll of sash slide pile with fin is around £21.60–£25.20 depending on pile height.

Some pile carries a thin plastic fin down the centre, which Historic England note makes a better seal. One supplier claims a single-fin low-friction pile gives markedly easier sash movement.

The honest catch. Self-adhesive pile sits proud of the surface. It eats into the 3mm running clearance rather than sitting recessed within it, so on a tight window it makes the sash stiff. The adhesive is the weak point — sash movement works stick-on seals loose over time. And it cannot properly seal the parting-bead gap at all, because that gap is behind the bead, not on its face. Applied to the face of the meeting rail on one sash it does genuinely help. Difficulty 2/5.

(d) Bead kits with integral pile — the best DIY route

This is professional-grade material bought over the counter, and for most people it is the right answer. Instead of sticking anything to the sash, you replace the beads themselves with versions that carry pile in a carrier.

Indicative trade prices, excluding VAT, in 3m lengths: timber parting bead with carrier and brush from about £4.75 (22 × 14mm) to £7.35 (8 × 25mm); heritage parting bead with 5.5mm pile set directly into primed timber and no plastic carrier, about £6.29; timber staff bead with carrier and brush from about £7.35 (20 × 15mm) to £8.19 (25 × 15mm); wood-composite staff beads about £4.94–£5.57 and parting beads about £3.99. Loose self-adhesive flat or T-shaped pile carriers are around £1.61 for 2.2m, with the carrier alone about £1.37.

Reckon on £30–£50 per window for a parting bead, two or three staff bead lengths, a meeting-rail carrier and the pile. A whole house of 8–12 sashes is roughly £250–£600 in materials.

What it fixes: the stiles and the parting-bead gap — the two biggest leakage paths — properly and reversibly. The parting bead alone accounts for a large share of the air leakage on most sashes.

What it does not fix: the meeting rails, unless you also fit a stick-on carrier there or rout the rail. And it will not help a sash that has dropped out of alignment.

Watch out: bead sizes vary a lot — parting beads are listed in 7 × 25, 8 × 25, 8 × 28 and 22 × 14mm, staff beads in 20 × 15, 20 × 20 and 25 × 15mm. Measure the original before ordering. Tools: chisel, flat bar, utility knife, a mitre saw or a good mitre block, pin hammer and panel pins, snips. Difficulty 3/5. See parting beads and staff beads for how to identify and remove yours.

(e) Routing your own groove, carrier and pile

Everything a professional job does, at materials cost — if the window is otherwise sound and you can also re-cord and re-balance it. A 710W palm router is around £59.99 and a six-piece cutter set about £22.99; dedicated cutters for flat and T-shaped carriers are roughly £35.55 and £27.30 excluding VAT. So £85–£120 of tools once, then £30–£50 of materials per window.

The groove itself: an 8mm straight flute cutter is the commonly reported size, cut to around 3.5mm depth for a flush fit. Some joiners prefer a 7mm cutter used hand-held with a fence rather than dragging a heavy sash over a router table. Bed the carrier with a silicone-based adhesive and slide the pile in once it has set.

Difficulty 4/5, and two hard stops. You are cutting into 120-year-old joinery with the sashes out, and a slip is not recoverable. More seriously, if your building is listed, Historic England names grooving specifically as a more invasive method that may affect special interest and may require listed building consent. Do not put a router into a listed sash without speaking to your conservation officer first.

One piece of arithmetic worth doing honestly: if you are buying a router and cutters to do one or two windows, most of the saving disappears. This route only makes sense across a whole house.

(f) Whole-window kits

Packaged kits sit between the bead route and a professional job. Prices seen in July 2026 run from about £60 for a kit covering a window up to 1.5m × 3m — staff and parting beads with fitted brush strips, 6m of waxed sash cord and meeting-rail strips — up to about £164.50 plus VAT for a fuller kit covering up to 2,950 × 1,450mm, which adds a pile carrier and 22m of brush pile, 14m of waxed cord, sash lifts, fasteners, locks, fixings, mastic and even sash weights. One cost guide puts DIY kits generally at £50–£100 per window.

The minimum tool list one supplier gives is worth repeating: hammer, chisel, multi-tool, cordless sander, snips, cordless drill and a small chop saw. The chop saw and the multi-tool matter most — beads need clean, accurate cuts, and a multi-tool frees old beads and paint lines without wrecking the surrounding joinery.

(g) Secondary glazing film and magnetic panels

A different measure that solves a different problem — and, on the numbers, the one with the best measured thermal payoff. Shrink-fit film is around £8.00 for 6m² at the DIY sheds or about £12.99 at the DIY sheds, with a one-year guarantee on both; clear window film is about £7.00 for 6m². Magnetic systems price the fixing only, from about £23.19 for a 5m kit, with the acrylic or polycarbonate sheet bought separately and cut to size; bulk magnetic strip works out around £2.24 a metre including VAT.

In Historic Scotland's measured testing, secondary glazing cut heat loss through the glazing by 63% and sealed secondary glazing cut air leakage by 97%. It is also the better sound insulator, because of the wide air gap. Historic England advise that installing reversible secondary glazing does not generally need listed building consent.

What it will not fix: rattle, sticking sashes, broken cords, or draughts once you open the window. Shrink film seals the window shut for the season — see the fire-escape warning below. The full comparison is on secondary glazing vs draught proofing.

(h) Curtains, shutters and blinds

Unglamorous, completely reversible, no consent implications, and better evidenced than most of the products in this list. From the same measured testing: heavy curtains cut heat loss through the glazing by 14%, a modern roller blind 22%, a Victorian roller blind 28%, timber shutters 51%, and insulated shutters 60%. If your house still has its original shutters, getting them working again is one of the best-value things you can do.

What they do not fix: the draught itself while they are open, rattle, or dust.

(i) Silicone, clingfilm and sealing a sash shut

Three budget tricks that genuinely work, with caveats that must not be skipped.

• Seal the sash shut with silicone. For a couple of pounds this removes the draught entirely. It is also close to final — undoing it properly means removing the sashes and servicing the window. The Energy Saving Trust make the equivalent generic recommendation for windows that do not open.
• Clingfilm pressed into the gaps with a blunt knife. No damage, invisible, and undone the moment you open the sash.
• Home-made secondary glazing — clear plastic sheet on a slender timber frame pinned into the reveal. Copes well with out-of-square openings and leaves only a few holes to fill.

Comparison table

How long DIY seals really last

Sources genuinely disagree here, and it is worth saying so rather than picking the flattering number. Claims in circulation range from 8–10 years for brush pile, through 15–20 years for a routed strip, up to 20–30 years for routed mohair or spring bronze. Against that, the actual manufacturer and retailer guarantees we could find are: one year on foam, four years on one brush pile product, five years on another.

The defensible position: the carrier is effectively permanent, and the pile is a consumable with a realistic service life of around 8–10 years. Because it slides out of the carrier, renewing it costs a few pounds rather than repeating the whole job. Claims of 20–30 years are not supported by any guarantee we could find.

What shortens it: painting over the pile, which is the number one cause of premature failure — specialists report repeat callouts caused by decorators glossing the seals. What extends it: cleaning the seals occasionally with warm soapy water so they do not become brittle.

When DIY is a false economy

These are stop signs, not difficulty ratings. If any apply, seals are not your first problem.

1. Painted-shut sashes. That is a stripping, freeing, re-cording and easing job, not a sealing job. And there is a real safety point: Historic England warns that a window firmly stuck in place may have assumed a structural role and be carrying the wall above, usually because a lintel has failed or moved. Such windows should not be forced — parts of a wall have been known to collapse — and the frame should be propped if there is any doubt.
2. Rot in the beads, cill, lower rails or the base of the stiles. Historic England is unambiguous that repairs come before draught proofing, and that simple repairs alone can cut air infiltration and heat loss by up to a third. Sealing a rotten window traps the moisture that is rotting it.
3. Broken or perished sash cords. You cannot fit a bead system without taking the sashes out, and you cannot take the sashes out without dealing with the cords — all four, plus the weights and the pockets.
4. Sashes that have dropped so the meeting rails no longer align. This is the single most common reason a DIY seal job "doesn't work". No amount of pile fixes misalignment; it just binds. The fix is re-cording, re-weighting and easing so the rails meet square.
5. Listed buildings. Stick-on strips are fine. Routing may need consent. Ask first.
6. Very slender frames. Historic Environment Scotland note that windows with very slender frames may be weakened by adding draught proofing — rarely mentioned anywhere else, and worth taking seriously.
7. Very large, heavy or leaded sashes, out-of-square frames, opened joints, or cracked and loose glass.
8. Rooms with open fires, stoves or gas or oil appliances. Historic England advise seeking specialist advice before sealing any such room. This is not a DIY judgement call.
9. The VAT arithmetic. DIY materials are standard-rated at 20%. An installer's supply-and-fit of draught stripping is currently zero-rated until 31 March 2027 under VAT Notice 708/6, with the relief covering the installation and materials supplied by the installer — but explicitly not materials you buy yourself. The gap between £40 of materials and a £350 fitted job is narrower than it looks. See the note on VAT.

The Energy Saving Trust's own position is worth quoting: professional draught proofing is likely to save more energy, because the installer knows which materials to use and where; older buildings often need extra care or specific materials; and you should get quotes from at least three reputable installers.

If you would like a price to compare against your materials list, send us the number of sashes and your postcode from the contact page, or read what a professional job includes.

Last reviewed: 28 July 2026.