Looking after your double glazing.
Double glazing is close to maintenance-free, which is not the same as maintenance-none. There is one job that genuinely decides whether your units are still clear in 2050 or fogged by 2035, and it costs nothing but a bit of wire and twenty minutes. Everything else on this page is optional. That one is not.
Your drainage slots decide your seal life.
Every window ever made leaks a little, on purpose. That is not a defect, it is the design. Wind-driven rain gets past the outer seal - AS 2047 tests for water penetration precisely because some always gets through - drops into the sill channel inside the frame, and drains back out through weep slots at the bottom. The system assumes water gets in and gives it a way out.
Block those slots and the water stays. It pools in the channel and sits against the bottom edge seal of your insulating glass unit, which is the one part of the whole assembly that cannot tolerate standing water. That is the most common reason a unit fogs at year 9 instead of year 24, and it is entirely preventable with a paperclip.
Three things block them around here. Silt, because the growth-corridor estates through Clyde North and Cranbourne East in the City of Casey, and Officer in the Cardinia Shire, have been building sites for a decade and everything is coated in fine clay dust. Spiders, who find a weep slot an ideal home. And silicone, applied by a well-meaning person who saw a hole in a window frame and assumed it was a fault. If you take one thing from this page: never seal a weep hole. Ever.
The twice-yearly job, in full.
- Clear the weep slots. Bottom of each frame, outside face. A piece of wire or a paperclip, then a squirt from a hose to confirm it runs through. Twenty minutes for a whole house.
- Wash the frames and seals. Warm water, a drop of dish soap, a soft brush. Salt, dust and pollen sit on the powder coat and hold moisture against it.
- Dry silicone on the compression seals. A wipe of dry silicone spray on a rag keeps the rubber soft and stops it taking a permanent set. This is the cheapest draught prevention that exists.
- Check the hardware. Any sash that needs a hip has dropped. Most rollers and hinges have adjustment screws and a quarter turn fixes it before wear sets in.
- Look at each unit in raking morning light. Ten seconds per window. You are looking for haze at the bottom corners, which is the earliest sign of edge-seal failure and worth catching while the warranty is live.
March and September are the natural times. Autumn ahead of the wet, spring after it. If you want the deeper explanation of what actually ages and in what order, that is on our how long double glazing lasts page.
Cleaning, and the four things that quietly cause damage.
Warm water, dish soap, microfibre, squeegee. Genuinely that is the whole method and it beats everything in the supermarket aisle. What matters more is the list of things not to do, because each one causes damage that looks like bad luck years later.
- No ammonia-based glass cleaner on any unit with exposed edge seals. Ammonia attacks butyl. It will not fog your window this year. It will help it fog in year 12.
- No pressure washer near a window frame, ever. The jet drives water past seals it was never designed to resist and straight into the cavity behind the frame. We have seen more damage from enthusiastic pressure washing than from any storm.
- No scrapers, scourers or abrasive pads on the powder coat or the glass. Paint flecks on new glass come off with a razor held flat by someone who has done it before, and not otherwise.
- No silicone in the weep holes. Worth saying twice.
Worked example: what two hours a year is worth.
Two houses in the same Cranbourne North estate, both retrofitted in 2011 with 16 openings of argon Low-E in thermally-broken aluminium, both around $19,000 in the money of the day.
House A cleared their weeps most autumns because the installer showed them how on handover day. Now at year 15, all 16 units are clear, seals still compressing, no work done beyond one set of rollers. On the numbers in our lifespan guide they should see year 24-25 before the first reglaze.
House B never touched them. The estate was still under construction for their first six years and the clay dust packed the slots solid. Three units on the west and south-west elevations have fogged - the ones that took the most weather. At $580-$980 each in 2026 money to reglaze from our pricing guide, that is roughly $2,300 spent at year 15, with the remaining thirteen on a similar trajectory. Call it $6,000 to $9,000 over the next decade that House A will not spend, against a 2026 whole-house retrofit of that size at $18,000-$26,000. The entire difference is about ninety minutes a year with a paperclip and a hose.
Seals: which ones are replaceable and which are not.
Two completely different things share the word "seal" and the confusion is expensive. The compression seal is the soft rubber the sash closes onto. It is a consumable, it goes hard after 10-15 years, and it is replaced for $80-$220 per opening. If your windows have started draughting and everything else looks fine, this is almost certainly your answer and it is cheap.
The edge seal is inside the insulating glass unit, holding the two panes and the argon together under AS 4666. It cannot be replaced, repaired, re-gassed or dried out. When it fails you reglaze the unit, which is a real job with a real cost but keeps your frame, hardware and paintwork - the full process is on our fogged IGU replacement page. Anyone offering to re-seal a fogged unit in place or "pump the gas back in" is describing something that does not exist.
One local note. Timber sashes carrying retrofit IGUs - common through Old Berwick and the older parts of Endeavour Hills - need paint maintenance the aluminium ones do not, roughly every 8-12 years depending on elevation. In exchange the frame has no expiry date at all, which is a trade most owners of a 1920s cottage take happily. That approach is on our retrofit existing frames page.
Maintenance questions.
What maintenance do double-glazed windows actually need?
Less than people expect, but not none. Twice a year, clear the drainage slots in the bottom of each frame, wash the frames and seals with warm soapy water, and put a dry silicone spray on the compression seals so they stay soft. Once a year, check the hardware and adjust anything that has dropped. That is the whole list and it takes about two hours for a full house. The drainage slots are the one that genuinely matters - a blocked slot sits the bottom edge seal in standing water and can take a decade off the unit.
How do I clean double-glazed windows without wrecking them?
Warm water, a drop of dish soap, a microfibre cloth and a squeegee. That is it. Never use ammonia-based glass cleaner on a unit with exposed edge seals, because ammonia attacks the butyl over time. Never use a scraper, a scourer or anything abrasive on the powder coat. And never pressure-wash a window frame - the jet drives water past the seals and into the cavity behind, which is the fastest way to create the exact problem you are trying to avoid.
Why are the drainage slots in my window frame so important?
Because every window leaks a little by design, and the slots are how the water gets back out. Wind-driven rain pushes past the outer seal, drops into the sill channel, and drains out through weep holes at the bottom of the frame. Block those with silt, spider webs or a well-meaning bead of silicone and the water has nowhere to go, so it sits against the bottom edge seal of the IGU. That single failure is the most common cause of an insulating glass unit fogging at year 9 instead of year 24.
Do double-glazed window seals need replacing, and how often?
The compression seals around the sash, yes - every 10-15 years. They go hard, take a permanent set and stop springing back, and once the sash is no longer landing on a soft seal you have a draught. Budget $80-$220 per opening. The edge seal inside the insulating glass unit is a completely different thing and cannot be replaced at all - when that goes, the unit is reglazed. Do not let anyone tell you they can re-seal a fogged IGU in place, because nobody can.
Does maintenance actually extend the life of double glazing?
Substantially, and mostly through one task. Keeping the drainage clear is the difference between a unit that fogs at year 9 and one still clear at year 25, because standing water against the bottom edge seal is what kills most units early. Everything else on the list is comfort and appearance rather than lifespan. Two hours twice a year, most of it spent poking a bit of wire through the weep holes and washing the frames, is genuinely the highest-return maintenance in the house.
Suburbs we service.
Not sure if that haze is a warranty claim?
Send us the install date and we will tell you where you stand before you spend anything. Free measure and honest advice across South East Melbourne.