Fitting windows is part of my trade, and most of the time, when people call me, it really is the right moment to replace them. But there are real signs, false symptoms, and a few cases where a repair is enough. Here is how I sort them out at your place, window by window.
A window does not die all at once. Entry-level uPVC lasts 15 to 25 years, well-maintained wood 20 to 50 years, aluminium 25 to 35 years. So the real question is not age: it is condition. And to judge condition, there are three places to look, in order.
1. Misting between the two panes. Not on them: between them. If you cannot wipe it off from inside or outside, the perimeter seal of the glazing unit is dead and the insulating gas has escaped. The glazing no longer insulates, and it cannot be repaired. On a recent, sound window you can replace the glazing alone; on a window of a certain age it is the signal for replacement, more on that below.
2. The frame. On a wooden window, gently push the tip of a screwdriver into the bottom of the : if it sinks in as if into cork, the wood is rotten and the window is at the end of its life. A warped frame, or sashes that rub or only close if you force them, tell the same story.
3. The mechanics and the seals. Draughts you can feel with your hand along the meeting edges, seals crushed and hard as plastic, a handle that turns without engaging. Careful here: these are symptoms that repair very well, and a salesman in a hurry will turn them into an argument for replacing everything.
The gold-underlined words are explained on hover. All definitions are in the joinery glossary.
Misting on the inside face is not a window disease. If condensation forms on the face you can wipe, the air in the room is too humid and the pane is simply the coldest surface. The treatment is ventilation: a serviced VMC (France's whole-house mechanical ventilation), clear air inlets, regular airing. New, more airtight windows can even make it worse if nothing else changes. I have seen it dozens of times, and it is the first thing I check on a visit.
Double glazing from the 2000s that is still sound is not an emergency. It insulates about half as well as new glazing, but the real gain from replacing it remains modest: the French state no longer subsidises that replacement anyway, the grants are reserved for single glazing. If yours is in good condition, your money will work harder in the loft or the walls. An odd thing for a joiner to write, but that is what the figures say.
"You will cut your heating bill in half": no. According to ADEME, the French environment and energy agency, windows account for around 14% of the heat loss of an older house. The roof and the walls each weigh twice as much. By replacing single glazing with recent double glazing, you gain in the order of 10 to 15% on heating, that is €170 to €250 per year on an average bill. That is already good, and the comfort gain is immediate: no more cold surface and draughts. But anyone who promises you double that is lying.
| Situation | The right answer | Indicative cost |
|---|---|---|
| Broken or misted glazing, recent and sound window | Replace the glazing alone | €80 to €200 per m² |
| Draughts, worn seals, window still sound | Replace the seals, adjust the hardware | €50 to €350 |
| Dead glazing on a window of a certain age | Replace the window | uPVC €450 to €800 fitted |
| Single glazing | Replace the window | uPVC €450 to €800 fitted |
| Rotten or warped fixed frame | Replace, with full frame removal | Wood €700 to €1,500 fitted |
Single glazing is not up for debate: it insulates four times less than recent glazing, and it is the only case where public grants still exist. For a complete house of 10 to 12 uPVC windows, expect €8,000 to €12,000 fitted, before grants.
My honest opinion: in most cases, when the symptoms are there, the best solution really is to replace the window. Glazing alone, I rarely change it: it makes sense when a unit is broken, cracked or misted on a recent window in good condition, not on a 25-year-old window whose seals, hardware and frame have aged along with it. Putting new glazing into a tired frame is like putting a new engine into a rusty car. Where I can really save you money is in the sorting: the windows of a house are not all the same age or the same exposure, and it is common to keep some and phase the rest, starting with the ones that hurt.
First, insist on the on the quote, not just the Ug: fine glazing in a mediocre frame makes an average window. Then be wary of the renovation installation sold by default: quick and clean, but it shrinks your glass area and requires a fixed frame in perfect condition. I explain both techniques in renovation installation or full frame removal, and the choice of material in uPVC, aluminium or wood.
On the grants side, the landscape is moving fast in 2026: as I write, a decree plans to remove windows from the single-measure route of MaPrimeRénov', the French state renovation grant, this autumn. The complete, up-to-date picture is in my article on window replacement grants. And I say it here rather than in the small print: I am not RGE certified (the French label required for most renovation subsidies). Reduced VAT at 5.5%, though, does not depend on that label but on the windows chosen: it applies when their thermal performance meets the required criteria, which I check and confirm on the quote. MaPrimeRénov' and the CEE bonuses, on the other hand, require an RGE artisan: you will not get them with me. On a window job these bonuses amount to a few tens of euros per window: I would rather make up for them with a fair price and careful fitting, and let you compare with full knowledge of the facts.
Finally, the fitting makes the window: very good glazing badly fitted loses most of its value in air leaks between frame and wall. That is the whole point of my window fitting page.
It is possible in specific cases: glazing that is broken, cracked or misted up, on a recent window in good condition. Expect €80 to €200 per m². In practice it is rare though: on a window of a certain age, the frame, the seals and the hardware have aged along with the glazing, and a complete replacement is almost always the better investment.
Not necessarily. Double glazing from the 2000s in good condition already insulates decently: the gain from replacing it with new units is modest, and the French state no longer subsidises it anyway. You replace when there is a real symptom: misting between the panes, a damaged frame, sashes that no longer close properly. Otherwise your money will be more useful elsewhere in the house.
If the misting is between the two panes, yes: the glazing unit is dead. But if the misting is on the inside face, the one you can wipe, the problem is air humidity and ventilation, not the window. New, more airtight windows can even make it worse if the ventilation does not keep up.
I come and look, I test every window, and I tell you which ones to keep, which to repair and which to replace. The quote is free and the decision is yours. I speak English, so feel free to call or write in English.
+33 6 03 57 45 47Reply within 48 hours, or in writing: contact@agencementklein.fr
