Window seal replacement cost: repair the seal or replace the glass unit
A failed window seal usually means the glass unit needs replacing, not the frame. The cost difference between the two is an order of magnitude. This is the distinction most homeowners miss, and it determines whether you pay EUR 200 or EUR 2,000 for the same-looking problem.
When a window seal fails (you see condensation between the panes, or the glass is fogged up and will not clear), the repair is almost always a replacement of the insulated glass unit (IGU), not the full window. Typical cost for IGU replacement is EUR 150–350 per window installed for standard double glazing (Werkspot glaszetter 2026, Homedeal dubbel glas vervangen). Full window replacement (frame, sash, and glass) runs EUR 440–700 per window for standard sizes (Homedeal). The distinction is the single biggest cost variable in the decision, and most homeowners never learn that the IGU option exists because contractors who make more margin on full replacements have no incentive to explain it.
What fails when a window “fogs up”
The IGU has failed. A modern double-glazed window is two sheets of glass separated by a spacer bar, with the gap filled by a dry inert gas (argon or krypton) and sealed at the perimeter with a desiccant-backed polymer seal. The whole assembly is the IGU, and it is the engineering object that makes the window thermally efficient. The frame holds it in place but contributes little to insulation.
The seal has a 15–25 year lifespan. When it fails, three things happen at once. The inert gas escapes, dropping the thermal performance. Moisture enters the sealed gap and condenses on the inside of the glass when the temperature drops. The desiccant inside the seal saturates, which is why the fogging worsens over time rather than clearing.
The frame, sash, hinges, and hardware are unaffected. The IGU is the only thing that needs replacing.
The diagnostic: IGU, frame seal, or frame itself
Run three checks before any quote. The three failure modes are independent and have very different price tags.
Condensation between the panes. Moisture or fog in the sealed gap between the two glass sheets (not the inside surface, not the outside) means the IGU seal has failed. The glass unit needs replacing.
Cold air at the frame edges. Hold a hand around the frame perimeter on a windy day. Cold air coming through means the frame weather seal or installation seal has failed, not the IGU. This is a much cheaper repair: a new rubber strip or re-caulk for EUR 30–80 per window, or close to free if you do it yourself.
Visible frame damage. Rot, warp, corrosion, or impact damage to the frame shifts the conversation to full window replacement. Wooden frames can sometimes be repaired; aluminium and PVC frames usually cannot once they are structurally compromised.
A reputable glazier walks through each check before quoting. A glazier who immediately quotes full window replacement without inspecting the IGU specifically is missing the diagnostic step. The reasons range: they may be cutting corners on a busy week, may specialise in full replacements and not do IGU swaps, may have judged the frame compromised already without saying so, or may be selling to homeowners who don’t know the IGU option exists. Each is something you can ask about before accepting the quote.
What the costs look like
Fair mandates in most European markets fall into five bands by scenario.
| Scenario | Typical scope | Fair mandate |
|---|---|---|
| IGU replacement, standard window, double glazing | ~1m² glass, standard frame fitting | EUR 150–250 per window |
| IGU replacement, larger window or triple glazing | 1.5–2m² glass or triple pane | EUR 250–500 per window |
| Frame seal or weatherstrip replacement | Rubber strip or caulk around frame | EUR 30–80 per window |
| Full window replacement (frame + glass) | Removal + new unit + fitting | EUR 440–700 per window |
| Full window replacement (heritage or special) | Listed building, unusual sizing | EUR 1,000–2,500 per window |
Source: Werkspot, Homedeal. Dutch BTW for renovation work is 9% rather than the standard 21%, applied to labour. Finnish kotitalousvähennys (35% of labour, max EUR 1,600 per person) and Swedish ROT-avdrag (30% of labour) further reduce out-of-pocket cost in those markets.
The IGU replacement is almost always the cheaper option when the frame is structurally fine, and “the frame is structurally fine” is the normal case for windows under 25 years old. Full window replacement is justified when the frame has failed, when multiple IGUs have failed within a short period (a pattern that suggests the rest are close behind), or when you are replacing as part of an energy-label upgrade.
The arithmetic: IGU vs full replacement
The question “should I replace the IGU or the whole window” is a specific case of the general repair-vs-replace calculation. Divide each cost by the years it buys.
For a 15-year-old frame with 15+ years of life left and a failed IGU:
- IGU replacement: EUR 250 / 15 years = EUR 17 per year
- Full replacement: EUR 600 / 30 years = EUR 20 per year
IGU wins. This is the typical result for windows under 20 years old with frames in good condition.
For a 25-year-old frame with 5 years of life left and a failed IGU:
- IGU replacement: EUR 250 / 5 years = EUR 50 per year
- Full replacement: EUR 600 / 30 years = EUR 20 per year
Now full replacement wins, because the IGU repair is being amortised over a short window before the frame itself needs replacing. The 50/30 rule catches this case: if the repair cost exceeds 50% of the replacement cost AND the component has less than 30% of its lifespan remaining, replacement is usually the better option.
See the repair-vs-replace guide for the full walkthrough.
When energy regulations change the question
Energy-label upgrades driven by EU or national regulations can override the per-year arithmetic. The Netherlands, Finland, Sweden, and the broader EU are tightening minimum energy performance standards for residential buildings, particularly for homes being sold or rented. A home with old single-glazed or early double-glazed windows may have a poor energy label (E, F, or G in the Dutch EPC system), and upgrading that label affects sale price, rental eligibility, and mortgage rates for some buyers.
In that situation, the full window replacement (with modern triple-glazed units in climate-appropriate markets) often makes sense even when the frame-level arithmetic says IGU repair would be cheaper per year. The reasoning is that the full replacement buys an improved energy label, which is an asset in its own right. Include the future sale-price uplift or the avoided cost of a mandatory upgrade at the point of sale in the calculation.
Worked example: Els in Utrecht
Els has a 1995 row house in Utrecht. The kitchen window has fogged up between the panes; the frame is sound, the hardware works, and the rest of the windows are dry.
Two glaziers visit. The first quotes EUR 950 for a full window replacement, citing “the seal is gone, easier to do the whole thing.” The second runs the three diagnostic checks: IGU is fogged, frame edges are tight, frame timber is sound. He quotes EUR 220 to swap the IGU only, retaining the frame.
The full-replacement quote is EUR 730 more for the same outcome from the kitchen window’s point of view. Els takes the IGU swap. The frame has another 15 years in it; the new IGU has 20. When the frame eventually needs replacing, the second IGU swap will be ready, and the total spend across both interventions will still be lower than the EUR 950 full replacement done now.
The lesson is not that the first glazier was dishonest. The lesson is that asking “which one is the problem, the IGU or the frame” is the question that decides whether you pay EUR 220 or EUR 950 for what looks identical from across the room.
Related guides
- What to do when something breaks in your house: the fix flow a failed window seal runs through.
- Repair, replace, or wait: the annual cost method: the annual cost arithmetic applied to IGU vs full window.
- How to set a mandate before calling your contractor: setting the mandate before the glazier arrives.
- What your warranty actually covers: a failed seal within 15–25 years may still be a manufacturer claim.
Glossary terms used in this guide
- Glossary: Component: the window as a distinct building element.
- Glossary: Consequential damage: moisture damage from an unaddressed failed seal.