Blog · 9 min read
When to replace
double glazing
Author: OKNA PLAST editorial team
- Published
- Updated
How to tell a cracked pane from a failed seal, what can be fixed on site and when the glass unit has to be swapped out.
OKNA PLAST is a window manufacturer with its own workshop and crews in Astana, so we decide on site whether a window needs replacing or the frame can be repaired. A failed seal, fogging inside double glazing or cracked window glass means new glazing; worn seals and fittings are a repair.
How to tell a failed unit from ordinary condensation
Water on the glass and a milky film look almost identical, yet only one calls for a new build. Telling them apart takes minutes.
Fogging inside double glazing and what it signals
Fogging inside double glazing signals a failed seal: damp has passed the butyl layer and reached the desiccant, and no cleaning brings the pane back. The spacer frame carries the butyl bead that keeps the cavity airtight; once it opens, vapour migrates inward, the desiccant saturates, and the argon fill escapes through the same gap. On a two-chamber window the haze usually starts as a thin streak along one edge, then spreads across the whole sheet within a season or two. A misted unit keeps losing its gas fill, so the glass feels colder and the room loses heat. Check the cavity against the light at an angle — a faint grey edge is the earliest sign worth acting on. Moisture resistance and dew-point limits for insulating assemblies are set out in GOST 24866.
If it is just condensation on the room side
- Dew point: damp settles on the coldest spot, so one cold section collects droplets first.
- Ventilation: sealed rooms with cooking and drying laundry push indoor humidity past the window's limit.
- Drainage: blocked slots in the profile trap water inside instead of letting it run out.
- Seals: worn gaskets let warm indoor air touch cold glazing and condense.
- Warm edge: an insulated joint around the opening keeps the edge above dew point in frost.
- The test: wipe the pane and watch for a day — haze clearing by noon points to airflow.
A quick self-check before you call anyone
- Look between the panes: haze or droplets trapped inside mean the seal has gone.
- Wipe the room side: water that clears and returns on cold mornings is condensation.
- Paper test at the opening: a sheet that flutters shows a draught at the seal, not the glazing.
- Check the edges: dark mould along the spacer points to a long-standing leak.
Repair or replace double glazing by type of damage
One fault, one verdict: when to replace double glazing and when repair is enough. We cover the cases we meet most often and show when repair closes the question.
A decision table for repair or replace window
| What you see | Likely cause | What we do | Outcome |
|---|---|---|---|
| Haze or droplets between panes | Failed seal | Replace the glazing | New unit |
| Cracked or chipped pane | Impact damage | Replace glass or unit | Fresh glazing fitted |
| Draught at the frame | Worn seal | Replace the seal | Repair |
| Stiff handle or sash | Worn fittings | Adjust or replace fittings | Repair |
| Water on the room side | Condensation | Improve airflow and edge | Repair |
When a repair is the honest answer
We repair rather than replace when the glass is sound and the fault sits in the seal, fittings or handles, since those parts wear out long before a glazed assembly. A draught along the frame line, a hard-turning handle or a sash dragging on the sill points to hardware, not glass, and swapping the whole thing would leave the real cause untouched. Our after-installation service covers adjustment, new seals and handles, part of the 13 services we run on windows we built. A pane with a clean, dry gap between the sheets has years left, so fresh glazing would fix nothing and hide the actual draught.
When only a new unit will do
- Lost seal: mist between panes means air and moisture entered; no reseal restores the gap.
- Saturated spacer: desiccant stops absorbing, so haze returns within weeks of any patch.
- Cracked pane: a chip or hairline weakens the sheet and cannot be bonded to full strength.
- Mould at the perimeter: a cold edge feeds dark spots; fresh glazing is the only cure.
- Cold draught through the cavity: once the barrier fails, the gap stops insulating and the room cools despite heating.
What actually gets swapped, the glass or the whole unit
A crack and a fogged pane lead to different jobs: sometimes only the sheet is renewed, sometimes the whole sealed assembly must come out.
Cracked window glass and how far the damage spreads
- Edge cracks: the whole assembly is replaced when a break reaches the edge, as a pane losing its seal fogs within a season.
- Chips near the frame: risky, opening the barrier to air and moisture so a small mark grows into a full swap.
- Tempered glass: shatters into fragments across the whole sheet, so one impact often means a complete new build.
- Laminated glass: the plastic interlayer holds fragments in place, buying time before the swap.
- Glazing beads: retainer strips clamping the sheet are renewed with it, since old ones crack and let water in.
- Pane thickness: a 4 mm sheet suits an inner layer, while outer ones in a cold city run thicker, matched at the survey.
Failed sealed unit versus a single pane
Broken double glazing versus a single pane. A failed sealed assembly means the whole build has gone, while a single cracked sheet is one layer inside it, so the two call for different amounts of work. A two-chamber build holds two air gaps and a total thickness of 32 mm, with the sheets tied together by a spacer bar and sealed at the perimeter. That barrier keeps the dry air in and the moisture out. Once it fails, haze forms between the sheets and no cleaning removes it. Swapping one layer by hand breaks the factory seal again, and the mist returns within weeks. The spacer bar and sealant work as one assembly, so the replacement goes in complete rather than as loose panes.
What we check before ordering a unit
- Frame and sash: we look for warp or rot that would spoil a fresh barrier.
- Fittings and handles: worn parts are flagged before the new build goes in.
- Seal condition: a perished gasket is replaced alongside the glazing.
- Rebate and thickness: we measure so the replacement fits the existing frame.
- Drainage: blocked drain slots are cleared to stop water pooling at the edge.
Choosing a unit for the Astana climate
A long frosty winter and strong wind set real demands on the glazing. We show which options hold warmth here and what each one gives you.
One chamber or two for a cold, windy city
We fit a two-chamber 32 mm build as standard for the capital, because the extra air gap holds warmth far better through a long frosty winter than a single-chamber one. That thickness pairs with a multi-chamber PVC profile to keep the inner pane warm. A single-chamber version is thinner and loses heat faster once the temperature drops and the wind picks up. The second gap matters most on the windward side of a flat, where a single-chamber build shows condensation within the first cold snap. If your flat faces the open steppe head-on, ask for the two-chamber build even where a slimmer one would fit.
Matching the glazing to the profile you already have
| Profile family | Chambers | Frame width | Build it takes |
|---|---|---|---|
| SMART | 4 | 60 mm | Two-chamber 32 mm |
| WDS premium | 5 | 60 mm | Two-chamber 32 mm |
| Deceuninck Favorit Space | 6 | 76 mm | Up to 44 mm |
| KBE 76 | 6 | 76 mm | Up to 44 mm |
| Rehau Geneo | — | — | Up to 52 mm |
Why the seal around the glazing matters as much as the glass
We install to GOST with a warm mounting seam and warm slopes, because here even a top-grade build still fogs if cold air reaches its edge through a thin joint. A three-layer seam keeps the frame edge above the dew point, so the pane stays clear on frosty mornings. Insulated reveals stop cold bridging at the sides, where thin plaster pulls moisture onto the pane. The frame is anchored for local ground movement as well as wind load, with a 9-point seismic allowance. Before handover we run a hand along the seam to confirm no draught reaches the glazing.
How the swap runs, how long it takes and what you can check yourself
From request to finished window, the path is short and predictable. Below are the stages, timeline, and what you check versus what the surveyor handles.
From request to finished window
- Survey: an engineer measures the rebate and thickness and gives a written scope.
- Contract: the price is fixed, with sill, flashing, slope trim, dismantling and installation included.
- Production: glass and profile parts are made in our own workshop and delivered by us.
- Installation: we fit within two weeks of the contract and finish sill, flashing and slope trim the same day.
- Handover: a personal manager stays with the order, so the scope does not drift.
Can you stay in the flat during the swap
You can stay in the flat while we swap a window, since the work is confined to one window at a time and the room is usable again the same day. Our own crews remove the sash, lift out the old glass, clean the rebate and seat the new one, then refit the bead and check the seal. Slope trim and the sill go back in the same visit, so the opening is closed before the crew leaves. Clearing the ledge and moving anything fragile a metre back is the only prep most rooms need, and it keeps the crew working at full speed.
What to leave to the surveyor
- Fair to try: wiping the room side of the pane and watching whether haze returns within a day.
- Fair to try: the paper test at the frame, holding a sheet where the sash meets the profile.
- Leave to us: measuring the rebate and exact thickness against the existing profile.
- Leave to us: ordering and seating a sealed unit so the spacer frame sits true.
- Leave to us: resetting the bead and checking the seal; wrong thickness cannot be trimmed on site.
When window repair can avoid replacing the insulated panel
The decision comes down to where the moisture sits and whether the glass itself is still whole. Here is the short version to carry with you.
- Haze between panes means a failed seal; cleaning won't restore the unit.
- Water on the room side is condensation, so check airflow and ventilation before ordering glass.
- A sound pane with worn seal or fittings needs repair, not replacement.
- A cracked pane or lost seal needs a fresh glazing assembly fitted in the existing frame.
- In a cold, windy city a two-chamber glazing unit and warm seam keep glass clear.
