A double hung sash that drops or rattles almost always has a worn balance or worn seals, while one that sticks usually has grit in the tracks or a frame that has moved out of square. The distinction matters because the first group is often repairable and the second frequently is not. Working out which you have takes a few minutes and saves considerable wasted effort.
How a double hung window works
Two sashes sit in the same frame and slide vertically. In most Australian aluminium versions only the bottom sash operates, though both may on some suites.
Three components make it work.
Balances counteract the weight of the sash so it stays where you leave it. Aluminium windows typically use spiral balances, a spring loaded rod running in the jamb, or block and tackle balances, a spring and pulley arrangement. Older timber windows used cords running over pulleys to counterweights hidden in the frame.
Jamb tracks and guides keep the sash aligned as it travels and stop it moving side to side.
Pile or brush seals sit in the jamb tracks and along the meeting rail, sealing against draught and rattle while still allowing the sash to slide.
Most problems come down to one of these three, and knowing which one narrows the diagnosis immediately.
Diagnosing a loose sash
A loose sash presents in one of three ways, and each points somewhere different.
It will not stay up. The sash drops when you let go, either slowly or immediately. This is a balance fault, and it is the most common double hung failure. A spiral balance loses tension over time, and a block and tackle balance can have its cord fray or break.
It rattles in wind. The sash moves side to side or front to back within the frame. This is worn pile seals, worn jamb guides, or both. Pile seals compress and degrade under Australian ultraviolet, and once the pile no longer fills the gap the sash has room to move.
It rattles at the centre. The two sashes knock against each other at the meeting rail. This is usually the cam lock, either not engaging fully or with a keeper that has shifted. Adjusting the keeper position often resolves it entirely.
Diagnosing a tight sash
It binds partway through its travel. Something is obstructing the track at that point, most often accumulated grit or a build up of old lubricant.
It is stiff throughout. Either the tracks need cleaning along their full length, or the balances are over tensioned, or the sash is slightly out of square.
It has become progressively harder over years. Corrosion in the tracks is likely, particularly near the coast, or the building has moved and the frame is no longer square.
It is tight only at the top or only at the bottom. The frame is racked, meaning pushed out of square. This is the diagnosis you least want, because it is rarely repairable.
What you can fix yourself
Clean the tracks. This resolves more sticking sashes than anything else. Vacuum the tracks rather than flushing them with water, which carries grit further in. Wipe out old lubricant residue with a dry cloth.
Use the right lubricant. A dry lubricant such as a PTFE or graphite based product. Do not use oil based sprays, which attract dust and eventually create a paste that binds worse than the original grit. Avoid silicone sprays near pile seals, since many seal materials do not tolerate them.
Adjust the meeting rail lock keeper. If the sashes knock at the centre, the keeper on the outer sash can usually be loosened, repositioned a millimetre or two and retightened so the cam draws the sashes fully together.
Replace pile seals. Worn pile is a common cause of rattle and draught, and replacement pile is inexpensive and available in standard sizes. It slides into a race in the jamb or sash. Match the pile height to the original, since too tall binds the sash and too short does not seal.
Check the sash is square. Measure both diagonals of the sash. If they differ by more than a couple of millimetres, the sash frame itself has racked and no amount of track cleaning will help.
The balance safety warning
Spiral and block and tackle balances store considerable energy.
A spiral balance is a spring under tension. A block and tackle balance is a spring in a housing. Both are holding enough force to counterweight a window sash, and both can release that force suddenly if disassembled incorrectly.
Balances have caused serious hand and eye injuries. They are not a component to open, dismantle or experiment with.
If a balance has failed, the correct approach is replacement rather than repair, and replacement generally requires removing the sash and knowing the correct tension and length for the suite. This is work for someone who does it regularly.
Two additional points. Balances are usually suite specific, so identifying the window system matters before ordering. And a sash whose balance has failed can drop unexpectedly, which is a genuine finger and hand injury risk, particularly where children use the window. Prop it or keep it closed until it is repaired.
When repair stops making sense
Several situations mean the window is past economic repair, and recognising them early saves money.
The frame is racked. If the frame itself is out of square, the sash will never run cleanly. Frames rack from building movement, from poor original installation, or from being distorted during transport or handling. Realigning a fixed aluminium frame in situ is rarely practical.
Corrosion in the tracks. Once the aluminium track surface has corroded and pitted, the sash runs on a rough surface and will keep binding. This is common within a few kilometres of the coast across the eastern suburbs, Northern Beaches and Sutherland Shire.
Balances are unavailable. Older or discontinued suites can be difficult to source parts for. A window that cannot be repaired today will not become easier to repair in five years.
Several windows are failing together. Individual faults are worth fixing. Multiple windows failing at once means the whole installation has reached the end of its service life, and repairing them one at a time is usually more expensive over a few years than replacing them together.
The window is single glazed and failing. If you are going to spend money on a window that also lets in heat, cold and noise, spending it on repair rather than replacement misses the opportunity. Our window replacement service includes assessment of whether existing windows are worth keeping.
While you have the window apart
Two things are worth checking whenever you are working on a double hung window.
Seals throughout. If the jamb pile has worn, the meeting rail seal has usually worn too. Replacing all of it at once costs little more and delivers a noticeable improvement in draught and noise. Seal condition affects acoustic performance considerably more than most people expect, as covered in our article on acoustic seals in double glazed windows.
Safety devices. If the property is a residential strata scheme in New South Wales, the window may be required to have a compliant safety device restricting how far it opens. Repair work is a natural moment to confirm one is fitted and functioning, since a seized or removed restrictor is a compliance problem as well as a safety one. See our article on choosing locks for double hung windows.
Preventing it happening again
Double hung windows are low maintenance but not no maintenance, and a small amount of attention extends their life considerably.
Vacuum the tracks twice a year, more often if you are near the coast or on an unsealed road. Grit is the primary cause of both wear and binding.
Wash the frames periodically. Near the coast this may also be a condition of your powder coat finish warranty, so it is worth checking the specific requirement.
Operate every window occasionally, including ones you rarely use. Balances and seals fare better with movement than with years of sitting still.
Use dry lubricant only, and sparingly. More is not better, and oil is actively harmful.
Attend to a sash that has started to feel different rather than waiting. A slightly stiff window is cheap to fix. A seized one that has been forced repeatedly often is not.
Summary
A sash that drops has a failed balance. A sash that rattles has worn seals or a lock that is not drawing the sashes together. A sash that sticks has grit in the tracks, corroded tracks, or a frame out of square.
Track cleaning, seal replacement and lock keeper adjustment are all reasonable to do yourself. Balance replacement is not, because balances store enough energy to injure and are usually suite specific.
Where the frame has racked, the tracks have corroded, parts are unavailable or several windows are failing together, repair stops being the sensible answer. Our double hung windows are manufactured in Villawood with balances and seals specified for Sydney conditions.
Frequently asked questions
Why does my double hung window not stay up?
The balance has failed. Spiral balances lose tension with age and block and tackle balances can have cords fray or break. Replacement is the fix, and it is not DIY work because balances store considerable spring energy.
What lubricant should I use on window tracks?
A dry lubricant such as a PTFE or graphite based product. Never oil based sprays, which attract dust and eventually bind the sash worse than before. Avoid silicone near pile seals.
Can I replace the pile seals myself?
Usually yes. Replacement pile slides into a race in the jamb or sash and is inexpensive. Match the pile height to the original, since too tall binds and too short does not seal.
My window is tight only at the top. Why?
That pattern usually means the frame is racked, meaning out of square. It commonly follows building movement or a poor original installation, and it is rarely repairable in situ.
Is it worth repairing an old double hung window?
It depends on what has failed. Seals, locks and track cleaning are worth doing. A racked frame, corroded tracks or unavailable parts generally are not, particularly if the window is single glazed and you would gain thermal and acoustic performance by replacing it.
How often should I maintain my windows?
Vacuum the tracks twice a year, more often near the coast. Wash the frames periodically, which may be a warranty condition on the finish. Operate every window occasionally, including the ones you rarely open.