How Long Does Double Glazing Last?

By Restoration Glazing, Chandler's Ford, Eastleigh · Last updated 13 October 2026

Double glazing usually lasts 20 to 30 years, but the parts wear out at different rates. The sealed glass units tend to go first, typically after 15 to 25 years, while a sound uPVC frame often outlives them. When a unit mists up, Restoration Glazing replaces just the glass unit from £120, keeping your frame, with a £180 minimum charge per visit.

How long does each part of a double glazed window last?

A uPVC double glazed window is really four things that age separately: the frame, the sealed glass unit, the moving hardware and the rubber seals. A frame lasting 20 to 30 years can need its glass, hinges or gaskets replaced along the way, and each of those can be done without a new window.

Industry guides give longer figures for other frame types: about 30 to 40 years for timber and 30 to 45 for aluminium, with care.

Want a price for yours? Call 023 8001 2328 or get a free quote online. For hinges, handles, locks or seals, pick your repair here.

What makes double glazing fail sooner?

Double glazing fails early when something keeps stressing the edge seal round the glass unit, which is its weak point. Sun, standing water and a poor fit are the usual causes.

• South-facing windows. Daily heating and cooling makes the glass expand and contract, which works the seal loose faster than on a shaded wall.
• Blocked drainage slots. uPVC frames have small drain holes along the bottom. When they clog with dirt, water sits against the bottom edge of the unit and attacks the seal.
• Coastal air. Salt air near Portsmouth, Fareham and the Southampton waterfront is harder on sealants and metal hinges.
• Poor fitting. A unit packed badly in the frame, or a frame fixed out of square, puts uneven pressure on the seal from day one.
• Never adjusting or oiling the hinges. A sash that's allowed to drop drags on the frame every time it closes, and that wears the hinges and gaskets. Looked after, hinges, handles, locks and gaskets usually last 10 to 15 years. Left dry and never adjusted, they can be worn out in a few. A drop of oil on the hinges and locks once or twice a year makes a real difference.

How do I know my double glazing needs attention?

The clearest sign is mist or droplets between the two panes that you can't wipe off from either side. That means the seal has failed and the unit has lost its insulating gas, and it won't clear up on its own. Our guide on why windows mist up explains what's going on inside the unit.

Other signs point to the hardware or seals rather than the glass:

• The window has to be lifted or slammed to close, or it scrapes the frame. Usually worn hinges.
• You feel a draught or hear whistling with the handle locked. Usually tired gaskets or a sash that's dropped.
• The handle turns but the window doesn't pull in tight. A worn lock or keeps.
• Water or black mould on the room side of the glass. That's condensation from the room, not a failed unit. If you can wipe it off, the glass unit is fine.

Is it worth repairing old double glazing or should I replace it?

If the frames are sound, repairing is almost always cheaper. Restoration Glazing replaces a misted unit from £120 and leaves the frame in place, while a new uPVC window is £350 to £800 fitted. Even several misted units usually cost less than new windows, as long as the frames are in good shape.

Repair makes sense when:

• the frames are straight, uncracked and still white rather than yellowed
• only some units have misted
• the problem is a hinge, handle, lock or seal

Our repair vs replacement guide runs through the sums for a typical house, and the double glazing repair cost guide lists every repair price.

When is double glazing not worth repairing?

Double glazing isn't worth repairing when the frame itself has failed, because new glass or hinges in a twisted frame won't seal properly for long. At that point Restoration Glazing will tell you a new uPVC window is the better spend.

• The frame is cracked, warped or split at the corners.
• The uPVC has gone badly yellow or chalky, a sign the plastic itself has broken down.
• Most of the units, hinges and seals have all gone at once, and the repair bill is getting close to the price of new windows.
• The sash won't sit square however it's adjusted.

We fit both, so we've no reason to push you either way. If a repair will do the job, we'll say so.

What happens when we replace a misted unit?

Replacing a sealed unit is two short visits: one to measure, one to fit. Each unit is made to measure, so we measure first and come back to fit it once it's ready. We usually measure the same week you get in touch and fit 2 to 3 weeks after that.

1. We check the window and confirm it's the unit that's failed, not the frame.
2. We measure the glass and note the type: clear, obscure, toughened or with Georgian bars.
3. The new unit is made to that size.
4. On the fitting visit we take out the glazing beads, lift out the old unit and fit the new one on fresh packers.
5. Beads go back in, we check the sash opens, shuts and locks properly.

Fitting takes 30 to 60 minutes per window. If a hinge or handle on the same window is worn, it's worth doing it on the same visit, since the £180 minimum covers the whole visit.

What guarantee comes with new glass or repairs?

Restoration Glazing guarantees replacement glass units for 5 years, repairs for 1 year and new uPVC windows for 10 years. Keep your invoice, as it's your proof of the date the work was done.

If your windows are still under a guarantee from whoever fitted them, check that first. Many installers cover misting for a set number of years, and a claim with them may cost you nothing.

What should you send us for a fast quote?

A photo of the window, a line about what's wrong and your postcode are enough for us to price most double glazing repairs.

• A photo of the whole window from inside
• A close-up of the misting, crack or broken part
• Rough size of the glass if you can measure it (width and height of the visible glass)
• What's happening: misted, draughty, dropped, won't lock, handle broken
• Your postcode

Use our misted glass quote form, email photos to enquiries@restorationglazing.com, or call 023 8001 2328.

Which areas do you cover?

Restoration Glazing repairs and replaces double glazing across Southampton, Eastleigh, Chandler's Ford, Winchester, Romsey and the rest of Hampshire, plus Salisbury, Basingstoke and Guildford, from our base at Unit 28 Monks Brook Industrial Park, School Close, Chandler's Ford, Eastleigh SO53 4RA.

We're FENSA registered (44665), and our team has 80 years of combined trade experience. For local detail see double glazing repair in Southampton.

What else do people ask about how long double glazing lasts?

How do I book a double glazing repair?

Call Restoration Glazing on 023 8001 2328, Monday to Friday, 8:30am to 5pm, or get a free quote online and send us a photo of the window. You can also email enquiries@restorationglazing.com.