Fogged unit? You need a reglaze, not a new window.
A cloudy double-glazed unit is not a broken window. It is a failed glass cartridge sitting inside a frame that is almost certainly still fine. Swapping the cartridge runs $580-$1,600. Replacing the window runs $2,400-$3,800. The entire skill is in knowing which one you actually need, and plenty of people get quoted the expensive one by default.
The seal failed. Nothing else did.
An insulating glass unit is a sealed cartridge: two panes, a spacer bar around the perimeter, a charge of desiccant inside that spacer, an argon fill, and a two-stage edge seal holding the whole thing together. AS 4666 is the Australian Standard that governs how it is built. The desiccant is the part people never hear about - it is a moisture sponge, and its job is to absorb the small amount of water vapour that finds its way in over the years, keeping the cavity dry.
Fogging is the moment that sponge is full. The desiccant is saturated, the seal has been leaking for a while, and now water vapour condenses inside the cavity where nobody can reach it. That is the whole story. It is not the glass, not the frame, not your cleaning, and not something you caused. It is a component reaching the end of its service life, typically somewhere around year 20-25 on a well-drained unit.
Worth saying early: a reglaze needs no permit. Because the unit drops back into the existing frame and the external appearance does not change, there is nothing for the City of Casey or the Cardinia Shire to assess - not even on the heritage-overlay streets through Old Berwick, where a full window replacement would need a planning permit. That is one of the quieter reasons reglazing beats replacing when the frame allows it.
The three-second test.
Try to wipe it. If the moisture comes off the inside face, the seal is perfectly fine and you are looking at ordinary condensation - the glass is colder than the dew point of your room air, which is a thermal problem, not a defect. If it comes off the outside face on a clear autumn morning, your double glazing is working beautifully and the outer pane is doing exactly what your windscreen does. If it will not wipe from either side, it is in the cavity, and that is seal failure. Once it has been going a year or two you will usually also see a faint tide mark or mineral streaking at the bottom corners. There is more on telling the three apart on our warning signs page.
Why "defogging" is not a repair.
You will find operators who drill a small hole in the pane, flush the cavity with solvent and warm air, and fit a tiny breather vent. The haze does go away and for a few months it looks like a miracle for a couple of hundred dollars.
Here is what you actually bought. The cavity is now permanently open to outside air. The argon is gone, so you have lost that portion of the thermal performance for good. The desiccant is spent and is not coming back. Humid air now moves in and out with the weather, so the unit hazes again on cold mornings and clears by lunchtime, forever. And you have a hole in a pane that was possibly toughened, which is a different conversation under AS 1288. It is not a repaired IGU. It is a vented double pane that performs worse than the day before you paid for it. We do not offer it and we would talk you out of it.
What a reglaze actually looks like.
A 2004 brick veneer in Narre Warren South, double glazed by the original builder. At year 21 the owner notices haze at the bottom corner of the 1,700mm x 1,150mm west-facing family room window on cold mornings. It clears by ten. Six months later it does not clear at all. Every other window in the house is perfect.
We measure the sight size and the glass thickness, check the frame is square and the drainage is clear - in this case it was not, which explains a great deal - and order a like-for-like unit: 6mm toughened outer, 12mm argon cavity, 6mm Low-E inner, warm-edge spacer, AS 4666 compliant. Six weeks to manufacture, because there is no such thing as a stock IGU.
Install day: beads out, old unit lifted, drainage slots cut properly this time, setting blocks positioned at the quarter points so the glass is carried by the frame rather than hanging on the seal, new unit in, beads back, done in about ninety minutes. Total $840. The frame, the hardware, the paint line and the reveal were never touched, and there is nothing to make good afterwards.
The alternative quote that owner received elsewhere was a full window replacement at $3,200, from someone who never checked the frame. Both quotes fix the fog. One of them costs $2,360 more and involves opening a wall. Our pricing guide has the full ranges, and the frame logic that decides between them is on our frame comparison page.
When a reglaze is the wrong answer.
Honestly, sometimes it is. If the frame is plain aluminium with no thermal break, putting a fresh $840 IGU into it is throwing good glass after a bad frame - that frame runs about 6.0 W/m2K and undoes most of what you are buying, which is the argument set out on our double-glazed windows page. If the frame is racked past adjustment or the sill is rotted through, same answer. And if six or eight units have gone in the same house at once, the economics shift toward doing the whole elevation properly rather than chasing them one at a time. We will tell you which of these you are looking at, at the measure, before you have spent anything.
Warranty first, always.
Before anything else, find the install date. A compliant AS 4666 unit carries a 10-year seal warranty and cavity fogging is exactly the covered failure. Check whether it is pro-rata - plenty are, meaning a year-9 claim returns 10 percent of the unit cost rather than a replacement. Ours are non-pro-rata for the full ten years. And do not waste time on your insurer: seal failure is gradual deterioration and it is excluded from every home policy we have read, which we have covered in detail on our insurance claims page. Also worth knowing why it happened to that one window: it is almost always the west elevation, or a blocked weep slot, and both are addressed on our Cranbourne page and in our retrofit approach.
Fogged unit questions.
Can a fogged double-glazed window be repaired without replacing it?
No, and anyone who says otherwise is selling something that does not work. There is a defogging technique where a hole is drilled in the pane, the cavity is flushed and a vent is fitted. It clears the haze for a while. What it also does is permanently vent the cavity to outside air, which means the argon is gone, the desiccant is spent and the unit is now a slightly worse-performing double pane that will haze again with the seasons. You have not repaired an IGU. You have converted it into a vented one.
How much does it cost to replace a fogged IGU in South East Melbourne?
For a like-for-like reglaze into your existing frame, expect $580-$980 for a small to medium unit and $980-$1,600 for a large one in 2026, including manufacture and fitting. That assumes the frame is sound and the glass is a standard build. Compare that with $2,400-$3,800 to replace the whole window and you can see why we always check the frame first. Reglazing keeps the frame, the hardware, the paintwork and the reveal untouched, and the job runs about ninety minutes per opening.
How do I tell seal failure apart from ordinary condensation?
Try to wipe it. If the moisture comes off, it is on the room-side face and the seal is fine - that is dew forming on cold glass and it is a thermal issue, not a defect. If it comes off the outside face on a clear morning, your double glazing is working exactly as designed. If it will not wipe off from either side, it is inside the cavity and the edge seal has failed. Seal failure also shows a characteristic tide mark or mineral streaking at the bottom corners once it has been going a year or two.
Is my fogged unit still under warranty?
Find the install date before you do anything else. A compliant AS 4666 insulating glass unit carries a 10-year seal warranty and edge-seal failure with visible cavity moisture is precisely what it covers. Read whether it is pro-rata: some warranties pay only a percentage by year, so a year-9 failure returns 10 percent of the unit cost rather than a free replacement. Ours are non-pro-rata for the full 10 years. Outside warranty it is simply a reglaze, and it is not an insurance claim - gradual deterioration is excluded from every policy we have read.
Why did only one of my windows fog when they were all installed together?
Because they did not all live the same life. The unit that fogs first is almost always on the west or north-west, where surface temperature can swing from 8 degrees at dawn to over 60 degrees on a 41-degree February afternoon, and that daily cycling works the seal harder than anything else. The second most common cause is a blocked drainage slot on that one frame, leaving the bottom edge seal sitting in water. Same house, same install day, same product - completely different workload.
Reglazing across South East Melbourne.
One cloudy window does not mean a new window.
Send us the install date and a photo and we will tell you whether it is a warranty claim, an $840 reglaze, or genuinely a replacement. Free measure across South East Melbourne.