Stuck Sash Window? How to Work Out Why It Won't Move

The split bottom rails and cracked staff beads we get called out to repair were mostly not caused by whatever jammed the window in the first place. They were caused by the twenty minutes of shoving that came afterwards. A stuck sash is giving you fairly specific information, and the remedy for one cause will damage the window if the real cause is another.

Thirty seconds of looking, before any force

Stand square to the window and look down the joint between the sash edge and the beads on either side. What you are looking for is a continuous paint film bridging the gap. If the last coat went on with the window shut, that film has glued the sash to the staff bead along its whole length, and pushing harder will only break something.

Then look at the bottom rail against the cill. Is it parallel, or is one end sitting lower? A sash that has racked in its box is a broken cord until proved otherwise.

Then look for hardware you had forgotten about. Sash stops, dual screws and Brighton bolts do exactly what they were fitted to do, and a locked window is not a stuck window. On a repainted sash the head of an engaged dual screw can be all but invisible under the film.

Four tests that name the fault

Do them in this order. They cost nothing, take a few minutes, and will usually settle it.

1. The one-corner lift. Put a hand under the bottom rail at the left-hand corner only, and lift. Then the right. With sound cords each corner should come up with very little effort, because the weight in that side of the box is carrying half the sash. A corner that feels like lifting the whole window unaided has a broken cord behind it.
2. The drop test. If the sash moves at all, push it a hand's width above the closed position and let go. It should stay exactly where you left it. If it sinks more than about an inch, the balance is out: a broken cord, a weight off its knot, or weights that were never right for the glass. If it will not hold at all, assume a cord has gone.
3. The knife test. Run a stiff filling knife down the gap between the sash edge and the staff bead. Hard, continuous resistance the whole length, and paint on the blade when it comes out, means a bonded film. If it drops down the gap freely and the sash still will not shift, paint is not what is holding it.
4. The listen. Rock the sash in its opening, an inch of movement is plenty, and put an ear against the pulley stile. A weight hanging free knocks softly against the inside of the box. A weight lying in the bottom of the box makes no sound at all.

If none of the four is conclusive, the staff bead has to come off, and that is where diagnosis ends and work begins.

Matching the symptom to the cause

Ranges only, and they move with access, storey, window size and borough. Anything above the ground floor needing external work carries access costs on top. Those six lines account for most of what our repair work on London sashes consists of in a normal week.

Paint, which is usually the answer

The commonest cause by a distance, and the least serious. Paint bonds the sash to whatever it touches, in three places: the stile against the staff bead, the sash face against the parting bead, and the bottom rail down onto the cill. On a window redecorated eight or ten times since 1900, the film in those joints can be thicker than a beer mat.

There is a second, separate paint problem, which is build-up rather than bonding. Every coat adds thickness to the beads and the sash faces, and the running clearance in a box sash was never generous. Enough coats and the sash is an interference fit before any glue effect comes into it. That one is not cured by scoring a line: it needs the beads off and the faces cut back. Which order to paint a sash in, and where the film has to stop, is set out in our guide to painting sash windows properly.

The lead question

Lead left British paint gradually rather than on a single date. White lead was still the main white pigment in joinery paint into the early 1960s, titanium dioxide displaced it through the 1950s and 60s, and lead pigments were out of general decorative use well before the legal backstop arrived. That backstop was the Environmental Protection (Controls on Injurious Substances) Regulations 1992, which prohibited the sale and use of lead carbonate and lead sulphate paints, with a narrow exemption for restoring Grade I and II* listed buildings, scheduled monuments and works of art. SPAB, who still recommend lead paint for eighteenth and nineteenth-century joinery where it remains permitted, are blunt about where the hazard lies: it is the dust, and dry sanding is the worst thing you can do to an old lead film.

On site, treat any sash carrying paint from before the 1970s as having lead under the top coats, and treat repainted period joinery as suspect, because you cannot see what is underneath. Do not dry-sand it, do not burn it off, keep children and food out of the room, and clean up with a damp cloth rather than a brush. Wet abrasion, a chemical stripper or low heat, with the debris bagged, is the sane approach.

Cords and pulleys are one job, not two

Every sash cord fails in the same place: the few centimetres sitting over the pulley wheel when the window is closed. That is the length which bends over the wheel on every operation, and it takes the abrasion of the wheel groove and the mouth of the pulley as well. Everywhere else the cord is only hanging. The other thing that kills cords is paint: a cord with paint driven into the plait cannot flex, so the fibres snap instead of bending.

Waxed cotton is still the right material for most period windows, in 6mm, 7mm or 8mm. Makers rate 6mm for a sash weight of roughly 30 to 35kg, 7mm for around 40 to 47kg and 8mm for 50 to 60kg, depending on whose cord you buy. A typical London sash carries around 4 to 9kg in each weight box depending on the glass, so the margin is generous and cords die of fatigue and abrasion long before they die of load. For scale, glass weighs about 2.5kg per square metre for each millimetre of thickness, which is why a large plate-glass Victorian sash is a different animal from a Georgian six-over-six.

The reason cords and pulleys are one job is the wheel. An axle pulley is a wheel of 1¾ inches (44mm) or 2 inches (50mm) across, with 2¼ inch wheels available for heavy sashes, running on a steel axle riveted through a brass or galvanised body and mortised into the pulley stile. It spends a century in a damp, unventilated box: steel axle, brass body and moisture make a straightforward corrosion cell, and the wheel gradually stops turning.

Once it stops turning, the cord is no longer rolling over the pulley, it is sawing across it. That is what the squeal is, and it is why a window with seized pulleys chews through cords. Test it with the staff bead off, spinning the wheel with the tip of a screwdriver. A sound pulley spins and coasts. A seized one turns grudgingly or not at all, and usually has a bright wear groove in one side. Load is rarely the issue on a domestic sash: even nylon wheels are rated by their makers to around 25kg and brass to roughly twice that, so the wheel is not overloaded, it is worn out. There is more on wear patterns and replacement in our piece on how sash pulleys wear.

If one cord has gone, the other three are the same age and have done the same work. Replace all four, and change the pulleys while the sashes are out, because the disassembly is identical and it is the second visit that costs money. The full sequence is in our walkthrough of replacing sash cords from pocket to parting bead.

Swelling, and what it is really telling you

Timber moves across the grain with humidity, and a sash that jams every January and frees off every July is moving with the seasons. But be precise about how much movement is genuinely available. The width of a sash is mostly two stiles, perhaps 45 to 50mm of timber each, and the glass between them does not move at all. A British year's humidity swing might account for a millimetre or so on each stile. Real, but rarely enough on its own to seize a window. What it does is finish off a sash already marginal from paint build-up, or one over-planed at some point that now sits skewed in the opening.

The more useful thing swelling tells you is that the sash is drinking. Timber that moves enough to jam is timber whose paint film has failed somewhere, usually at the bottom rail, the meeting rail or around the putty. So a sash that only sticks in winter is not really a sticking problem. It is an early rot problem, and it wants stripping, drying, filling and repainting rather than planing. Plane a swollen sash in February and you own a rattling sash in August.

The obstructions nobody thinks to check

The category that produces the most sheepish call-outs.

• Screws or nails driven through the staff bead into the sash. Usually somebody's idea of security, sometimes a decorator pinning a loose bead.
• A sash stop, dual screw or Brighton bolt engaged and then painted over, so the head has vanished into the film.
• Parting bead refitted proud, or a replacement of the wrong section, pinching the sash down its length. How those beads should sit is covered in staff beads and parting beads.
• The sash racked in the box after a cord failure, so one corner is high and the whole thing is cocked. Measure the gap above the meeting rail at both ends: more than a couple of millimetres of difference is your answer.
• Sash horns fouling the head lining, after a frame has moved or a sash has been rehung in the wrong opening.
• Debris in the box. A weight off its knot and jammed sideways across the pocket will stop everything, and no force at the bottom rail will shift it.

Freeing a painted-shut sash, in order

1. Score the film on the inside face, running a blade down the joint between the sash and the staff bead on both stiles, and along the bottom rail where it meets the cill. Several light passes, not one deep one.
2. Do the same on the outside if you can reach it safely. Most people skip this and then wonder why nothing shifts. If you cannot reach it from a safe position, stop here and get someone who can.
3. Work a broad filling knife into the joint and lever gently against the frame, never against the glass and never against the beads. Move along every 100mm rather than trying to break the joint at one point.
4. Tap the bottom rail upward with the heel of your hand, or a rubber mallet on a softwood block spanning the full width. Never a bolster or a chisel on the meeting rail. It splits along the grain, and a new meeting rail is a joinery job.
5. Once it moves, keep it moving. Run it up and down its full travel several times so whatever film remains breaks cleanly instead of tearing.
6. Then find out why it was painted shut, and deal with that, or you will be doing this again in three years.

Where to stop

Stop if the window is in a listed building and freeing it would mean cutting into original fabric: that consent question belongs with your council's conservation officer before the blade comes out. Stop if the glass is old and visibly wavy. And stop if the diagnosis came back as cords, because that means beads out and sashes out of the box, and beads two centuries old do not forgive a wrecking bar.

What a competent homeowner can genuinely take on is set out in our list of the five sash faults you can fix yourself, and if you want to understand the balance before you open the box, start with how a sash window is counterweighted.

Of everything here, cords are the one fault where waiting costs real money. A sash hanging on a single cord racks every time it is moved, and a racked sash wears grooves into its own stiles and scours the parting bead alongside them, so a half-day sash cord replacement turns into a joinery repair if it is left a winter or two. If the drop test told you the balance has gone, book that one first.