The early warning signs your windows are done.
Windows almost never fail suddenly. They decline over five or ten years through a sequence most people never connect: a sash that sticks, a draught you can only find on a windy day, mould in one corner of one room, a heating bill that creeps. Here is the sequence, what each stage actually means, and which ones are a $120 fix rather than a $22,000 one.
Condensation is three different problems wearing the same coat.
Start here, because more money gets wasted on misreading condensation than on any other window symptom. Which surface the water is sitting on tells you everything, and it takes four seconds to check with a finger.
- Room-side, wipes off. The inner face of your glass is colder than the dew point of the air in the room. This is a genuine problem and it is the one double glazing was invented to solve. On a single-glazed window in a Berwick bedroom at 6am in July the glass sits near the outside temperature, and every bit of moisture your family breathed out overnight lands on it.
- Between the panes, will not wipe off. The edge seal has failed and moisture is inside the cavity. That unit is finished - not repairable, not dryable, not topped up with gas. It is a warranty claim if it is under 10 years old and a reglaze if it is not.
- Outside face, on a clear morning. Your double glazing is working. The outer pane is thermally isolated from the warm house, so it drops to ambient and dew forms on it exactly like it does on the car. Every single autumn we get calls about this. It is the best possible news and it burns off by nine.
The seal-failure version is covered properly on our fogged IGU replacement page, including why you cannot just swap one pane. The room-side version is a design problem, not a defect, and the fix is on our Low-E energy glass page.
The sequence, roughly in order.
Year one of decline: the sash gets harder to close. You start using a hip. This is the frame racking, and in the southern Casey corridor it is usually the ground doing it rather than the window. More on that below.
Then: a draught you can only find deliberately. Wet the back of your hand and run it around the reveal on a windy day, or hold a candle near the closed sash and watch the flame. Compression seals go hard and take a permanent set after 10-15 years, and once the sash stops landing on a soft seal you are heating the street. This is often a genuinely cheap fix - $80-$220 per opening for hardware and seal replacement - and it is worth doing before you consider anything bigger.
Then: the reveal starts talking. Hairline cracks at the corners of the plaster, a paint line above the head that keeps reopening however many times you fill it. That is movement, and filler will never win against it.
Then: mould in one corner of one room and nowhere else in the house. That is a cold bridge plus still air plus condensate. It is not a cleaning problem and bleach is not a fix.
Then: you notice the traffic. By the time the Monash or the Princes Highway is louder than it used to be, your seals have been gone for years. Air paths and sound paths are the same paths.
The test that decides repair versus replace.
People assess windows by looking at the glass. Glaziers assess them by looking at the frame, because the frame casts the deciding vote almost every time.
If the frame is square, structurally sound, and the sash still lands on its seal, then virtually everything you are experiencing is a repair. Rollers, hinges, stays, compression seals, blocked drainage slots, tired glazing beads - all consumables, all cheap, all worth doing. A house full of sound timber sashes with worn hardware is not a replacement job. It is a service.
If the frame is racked past adjustment, rotted through at the sill horns, or is 1980s-1990s aluminium with no thermal break, you are replacing whatever the glass looks like. That last one is the case people find hardest to accept: a plain aluminium frame is a strip of metal connecting outside to inside, and it conducts heat almost as badly as the single pane it holds. Putting a beautiful argon Low-E IGU into it is like fitting a good door to a tent. That is the whole argument on our double-glazed windows page, and the reason we quote frame replacement on growth-corridor housing and IGU retrofit on original timber. Which one your house is depends on when it was built - the split across the corridor is set out on our Berwick page.
Worked example: what the diagnosis is worth.
A 1979 Endeavour Hills brick veneer, 14 openings, original timber frames. Owner rings convinced the whole lot needs replacing - streaming condensation, three sticking sashes, mould in the south bedroom, heating bills at $640 a quarter. A full replacement in thermally-broken aluminium from our pricing guide would be $18,000-$26,000 at 2026 rates.
What the measure actually found: twelve of the fourteen timber frames sound under the paint, two with sill rot needing splicing. So the job became an IGU retrofit into the existing sashes at roughly $14,000-$19,000 in 2026 money before rebate, two sills spliced at about $600, all fourteen sets of seals and hardware refreshed, and drainage slots cut into the two that never had any. After a VEU rebate of about $2,900 the out-of-pocket landed near $12,400 - and the original 1979 frames stayed, which is what the owner actually wanted once someone told them it was possible. Their next-door neighbour, same era, same street, had aluminium frames retrofitted in 1994 and needed full replacement. Same symptoms, opposite answer. That is why nobody should quote your windows over the phone.
When it is the ground, not the window.
Cranbourne, Hampton Park, Lynbrook, Lyndhurst and much of the flat southern Casey plain sit on highly reactive clay, classed H1 or H2 under AS 2870. That soil swells with winter rain and shrinks in a dry February, and the slab and frames ride with it. A window that binds every August and frees up every February is describing your soil, not a defect - and replacing it with a new window on the same slab buys you a new window that also binds every August. Fix the drainage and the site fall first. If a frame binds and never releases again, it has taken a permanent set, and that one genuinely is finished. Local detail is on our Hampton Park page and the standards references sit on our local trades page.
Diagnosing your windows.
How do I know if my windows need replacing or just repairing?
Test the frame, not the glass. If the frame is square, sound and the sash still closes onto its seal, almost everything else is a repair - hardware, seals, drainage, beads. If the frame is racked, rotted through, or is 1980s aluminium with no thermal break, you are replacing regardless of what the glass looks like, because a non-thermally-broken aluminium frame conducts heat almost as badly as the single pane sitting in it. The glass is rarely the deciding vote. The frame nearly always is.
Is condensation on my windows a sign they need replacing?
It depends entirely on which surface the water is on, and this is the single most useful thing to know. Water on the room-side face that you can wipe off means the glass is colder than the dew point of the air in the room - a real problem, and exactly what double glazing fixes. Water between the panes that you cannot wipe off means the edge seal has failed and that unit is finished. Water on the outside face on a clear autumn morning means your double glazing is working beautifully and you should leave it alone.
What are the early warning signs before a window actually fails?
The sash gets harder to close over a season or two, which is the frame telling you it is racking. Then a faint draught you can find with a candle flame or a wet hand on a windy day. Then the corners of the reveal start showing hairline cracks in the plaster or a paint line that keeps opening up. Then mould in the corner of that room and nowhere else. By the time you can hear the traffic more clearly than you used to, the seals have been gone for a while. None of these are dramatic and all of them are cheaper to address early.
Why do my windows rattle and stick more than they used to?
In most of the flat southern part of the City of Casey it is the ground, not the window. Cranbourne, Hampton Park, Lynbrook and Lyndhurst sit on highly reactive clay classed H1 or H2 under AS 2870, and that soil swells in winter and shrinks through summer. Your frames move a few millimetres with the slab every year. A window that binds every August and frees up every February is telling you about your soil. If it binds and never frees up again, the frame has taken a permanent set and it is time to talk.
My heating bill keeps climbing but nothing looks broken. Is it the windows?
Very likely, and it is the least visible failure of the lot. Glazing is typically the weakest part of the building envelope, and a single-glazed aluminium window runs a U-value around 6.0 W/m2K against roughly 0.5 for the insulated wall beside it. Nothing looks wrong because nothing is broken - the window is simply doing what it always did, and your heating is doing more work every year as seals age and draughts open up. A whole-house retrofit typically takes 20-35 percent off heating and cooling costs.
Free assessments across these suburbs.
Get an honest read before you spend anything.
We will tell you which openings are a $150 service and which are genuinely finished. Sometimes the answer is "your windows are fine, fix the drainage". Free measure across South East Melbourne.