What Is Double Glazing Replacement?
Double glazing replacement is the work of renewing double glazed windows that have stopped doing their job, either by changing the sealed glass units inside frames that are still sound or by taking out the whole window and fitting a new one. A great deal of Kent's double glazing went in during the 1980s and 1990s, when estates in Dartford, Gravesend, Sittingbourne, Ashford and the Medway Towns were re-windowed street by street. Many of those units have now lost their seals, and many of those frames were made to thermal standards well below today's.
The key decision is how far to go. A single fogged pane in a well-fitted frame usually needs nothing more than a new unit. A house where every window has discoloured, the hinges have worn and several units have failed is often cheaper to put right in one go. A good surveyor will tell you honestly which of those you are looking at.
Signs Your Double Glazing Needs Replacing
- Mist, droplets or white staining trapped between the two panes that cannot be wiped away
- A faint rainbow or smeared look on the inner surfaces of the glass, which often shows the cavity has been damp for years
- Black or perished gaskets that let rain track in behind the glass after a south-westerly storm
- uPVC that has yellowed, gone brittle or cracked at the welded corners
- Openers that have dropped so far they drag on the frame, even after the hinges have been adjusted
- Energy bills or cold spots suggesting the glass is an early low-performance unit without any coating
Replacement Options Explained
- Sealed unit only. The beads are removed, the failed unit comes out and a new one made to the exact size goes in. The frame, hinges and locks stay. Modern units with a low-emissivity coating, argon fill and warm-edge spacer are noticeably warmer than the unit they replace.
- Units plus hardware. New glass together with new friction hinges, handles and gaskets, which can bring a tired but structurally sound set of windows back into good working order.
- Full window replacement. The whole frame is cut out and a new window fitted, usually in uPVC, aluminium or timber, with the latest glass and locking specification.
- Whole-house renewal. Every window replaced in one project, often with a change of colour or style at the same time. This is where a consistent specification across all rooms matters most.
- Triple glazing or acoustic glass. An option for north-facing rooms, homes near the M20 or M2, or properties by the railway, though it adds weight and cost.
What to Include When Asking for a Quote
Separate the windows with a failed unit from the ones that are simply old. Walk round the house on a cool morning and note which panes are fogged inside the cavity, then say how old the frames are if you know, and whether any unit has been replaced before. A replacement-unit firm needs the rough size of each affected pane and whether it is toughened; a small kite mark etched in a corner of the glass tells you, and a photograph of it saves a second visit.
If you are leaning toward new frames, tell installers what you dislike about the current ones: poor locks, low-level panes you cannot open, frames too bulky for the openings or white you no longer want. Mention any windows that open over a flat roof or conservatory, any upstairs room that relies on a window as its escape route, and whether you are on a noisy road where acoustic glass is worth pricing.
A clear quote for units only should list each unit by size, glass type and spacer, and say whether new beads and gaskets are included. A quote for full replacement should give the frame system, colour, glass specification and whole-window energy rating for each window, and say how the old frames will be removed and disposed of and how the reveals will be made good.
How Much Does Double Glazing Replacement Cost?
| Job size | Typical cost |
|---|---|
| One or two misted sealed units swapped in sound frames | £150 – £600 |
| Several complete windows, such as the front of a semi | £1,800 – £5,000 |
| Every window in a three-bedroom house renewed | £5,000 – £10,500+ |
These are guide figures, not quotations. Coloured or woodgrain frames, triple or acoustic glass, bays and upstairs access all add cost. Always check whether VAT, disposal and making good are included.
The Replacement Process: What to Expect
- Survey. The installer checks each window, confirms which units or frames have failed and measures for manufacture.
- Specification. You agree frame colour, opening layout, glass type and any upgrades, and receive a written quote.
- Manufacture. Sealed units can take one to two weeks; complete windows usually take several weeks.
- Fitting. For units only, beads are removed and glass swapped in a couple of hours per window. For full replacement, old frames are cut out, new ones fixed and sealed, and cills and boards fitted.
- Handover. Every opener is checked for smooth operation and locking, trickle vents are demonstrated, and you receive your guarantee and certificate.
Planning Permission and Building Regulations
Replacing like with like on a house is normally permitted development and does not need planning permission. Flats, listed buildings and properties in conservation areas covered by an Article 4 direction are the usual exceptions, and a change of material or style may need consent. Replacing just the glass unit in an existing frame is a repair and falls outside the Building Regulations.
Replacing the whole window is controlled work. It must meet thermal, ventilation, safety glazing and escape requirements, and is normally certified by an installer registered with a competent person scheme such as FENSA or Certass. The government's competent person scheme guidance explains how that works; without a registered installer, you would need a building control application.
How to Choose a Double Glazing Replacement Installer
- Would you recommend replacing units only, or are the frames themselves past saving?
- What coating, gas fill and spacer bar will the new units have?
- What is the whole-window energy rating of the frames you are proposing?
- Are you registered with a competent person scheme, and will you register the job?
- How long are the guarantees on sealed units, frames, hardware and workmanship?
- How will you protect floors and furniture, and how will the reveals be finished?
Frequently Asked Questions
Can I replace just the misted glass rather than the whole window?
Usually, yes. If the frame is square, the hinges work and the gaskets are sound, a new sealed unit can be made to size and fitted into the existing frame, typically in under an hour once it has been made.
How long does double glazing last before it needs replacing?
Sealed units commonly last twenty years or more, but units in exposed or badly drained frames can fail sooner. Frames often outlast the glass, which is why swapping units is worth considering first.
Will new double glazing reduce condensation inside my home?
It usually reduces condensation on the glass because the inner pane stays warmer, but new windows are more airtight, so trickle vents and extractor fans need to be used to keep indoor humidity down.
Do I need a FENSA certificate if only the glass is replaced?
No. Changing a sealed unit in an existing frame is a repair and does not need Building Regulations certification. A certificate is required when the whole window, including the frame, is replaced.