How to fit a window seal so the sash still locks
Updated: October 2026
You have a self-adhesive roll and a casement that whistles. How to fit a window seal is finished only when the sash still shuts and the handle still locks. Stick the strip to the fixed rebate, try about 50 mm before you commit the roll, and peel it off if the lock will not meet. Listings sit on the [window seal comparison](/hub/door-and-window-security/window-seal). Products Compared checked public UK advice and the amazon.co.uk fitting lines on 15 October 2026, with no laboratory lock test. A qualifying purchase can earn a commission at no extra cost to you.
You have a self-adhesive roll and a casement that whistles. How to fit a window seal is finished only when the sash still shuts and the handle still locks.
You have a self-adhesive roll and a casement that whistles. How to fit a window seal is finished only when the sash still shuts and the handle still locks. Stick the strip to the fixed rebate, try about 50 mm before you commit the roll, and peel it off if the lock will not meet. Listings sit on the window seal comparison. Products Compared checked public UK advice and the amazon.co.uk fitting lines on 15 October 2026, with no laboratory lock test. A qualifying purchase can earn a commission at no extra cost to you.
Our top picks
| Badge | Product | How it fits | Suitable gap | Fitting | Note | Price | Offer |
|---|---|---|---|---|---|---|---|
| Best overall |  YANKUIRUI YANKUIRUI D-profile foam seal, 6 m, white | Self-adhesive | 3–6 mm | Scissors, no drilling | 8.6 | about £4.49 | View offer |
| Best value |  UPSEN UPSEN D-profile foam seal, 10 m, white | Self-adhesive | About 3.5–5 mm | Scissors | 8.3 | about £4.99 | View offer |
| Alternative |  Esufeir Esufeir D-shape rubber seal, 6 m, black | Self-adhesive | 2.5–6 mm | Scissors; wipe included | 5.4 | about £7.99 | View offer |
On this page
Test 50 mm before you commit the roll
Test about 50 mm of self-adhesive window seal on the fixed rebate before you cut the roll. The Centre for Sustainable Energy puts that piece on the frame, near the edge closest to you, and keeps it off the moving leaf. Close the casement and slide a plastic card into the gap. A comfortable fit is the pass, a forced card means the strip is too thick, and a card that falls out means it is too thin. The Energy Saving Trust says a thin strip leaves the draught. A thinner profile is on the window seal buying guide. Only then cut the perimeter.
Clean the rebate and stick to the frame
Wipe the fixed rebate with a damp cloth, lift loose paint, and let it dry, which is B&Q's order. White spirit is the National Residential Landlords Association step for a greasy rubber strip, and YANKUIRUI, UPSEN and Bynsaer do not require a solvent. Stick the strip to the rebate the sash closes onto, in short sections, and do not stretch it. That face is inside the opening, not the weather face of the wall. Peel a little backing at a time. WanderGo's backing paper can be awkward. Cut with scissors. Do not drill the frame.
Corners, vents and the lock
Cut the corners so they meet flat. B&Q's neat finish is a 45-degree cut on the meeting ends, so the joint does not hold the sash off the frame. Do not run one stretched length around the corner. Trickle vents, air bricks and boiler flues stay open. Approved Document F keeps background ventilation. Close the sash and turn the handle. If the window will not meet, peel the strip off.
When this method is the wrong job
This sequence is for a stick-on strip on a casement or a timber rebate. On a vertical sliding sash, foam does not work well, because the sashes have to slide. A brush seal, or a sash specialist, still lets them move. A dropped sash or a glazing-bead seal needs a fitter. A perished uPVC groove needs a push-in seal rather than foam stuck over it. Matching that foot is on how to replace a uPVC window seal. Foam tape or a window gasket sets the choice between those two.
Common questions
Do I stick the seal on the frame or on the opening sash?
Stick it on the fixed rebate the sash closes onto, near the edge closest to you. The Centre for Sustainable Energy and the National Residential Landlords Association both place a casement strip there. The weather face of the outside wall leaves the gap open. A strip on the moving sash travels with the leaf and misses that gap.
How do I test the thickness before I use the whole roll?
Cut about 50 mm, press it on the frame, close the window, and slide in a plastic card. A comfortable fit can stay. A forced card means the strip is too thick, and a card that falls out means it is too thin. Remove the piece before you cut the roll. The Energy Saving Trust says an oversized strip may stop the window closing.
What should I clean the rebate with?
Wipe with a damp cloth, remove loose paint, and let the rebate dry before you peel the backing. That is B&Q's order for a stick-on strip. White spirit is for a rubber strip on a greasy frame, and YANKUIRUI, UPSEN and Bynsaer do not require a solvent.
Should I stretch the strip to make it reach?
Press the strip as it lies, in short sections, without pulling it to the corner. B&Q and the National Residential Landlords Association both say not to stretch it. A stretched foam strip can shrink back and open a gap. If the roll stops short, cut a new piece so the ends meet.
What if the handle will not lock afterwards?
Peel the strip off if the handle will not lock. The seal is too thick, or a piled corner is holding the sash off the frame. An Esufeir review described a back-door lock under strain after a full perimeter. Forcing the handle is not a fix. Try a thinner strip only after a fresh 50 mm card test.
Can I use this method on a sash window?
Use a brush seal, or a sash specialist, on a vertical sliding sash. The Energy Saving Trust and the Centre for Sustainable Energy say foam does not work well there, because the sashes have to slide. A dropped sash, or water at the wall joint, needs a fitter.
Can I cover a trickle vent that whistles?
Leave the trickle vent open, even if it whistles. The Centre for Sustainable Energy says not to block trickle vents, air bricks or boiler flues, and not to seal a kitchen or bathroom with no extractor. Approved Document F keeps background ventilation, so covering the vent is outside this job.
Related pages
Sources
Public UK sources named in the research digest. Listing prices and ratings are the amazon.co.uk figures saved on 15 October 2026.
- Energy Saving Trust — Draught-proofing (retrieved October 2026)
- Centre for Sustainable Energy — DIY draught-proofing (retrieved October 2026)
- GOV.UK — Approved Document F (2026) (retrieved October 2026)
- BSI — BS EN 12365-1:2003 gasket and weatherstripping (retrieved October 2026)
- Seals Direct — How to measure a replacement glazing gasket (retrieved October 2026)
- Fixtrade — How to replace the rubber seal on uPVC windows (retrieved October 2026)
- Historic England — HEAG084 Draught-proofing windows and doors (retrieved October 2026)
- Consumer Rights Act 2015 (retrieved October 2026)