What Is Double Glazing Replacement?
Double glazing replacement is the work of renewing double glazing that has failed or reached the end of its useful life. It covers two quite different jobs. The smaller one is swapping individual sealed glass units that have misted up, while keeping the existing frames. The larger one is replacing whole windows, frames and all, where an older double glazing installation from the 1980s or 1990s is worn out. Many Hampshire homes had their first double glazing fitted in that period, and a lot of it is now thirty or more years old.
The first question is always whether the frames are still sound. Where only the glass has failed and the frames still close and lock properly, new sealed units may be all that is needed. If the frames themselves are failing, putting new glass into them rarely makes sense.
Signs You Need Double Glazing Replacement
- Misting or condensation trapped between the two panes of a sealed unit
- A milky film or water marks inside the unit that cannot be cleaned
- Cracked or broken glass in an otherwise sound frame
- Old aluminium double glazing with no thermal break, which is cold to the touch and runs with condensation
- Early uPVC frames with split welds, perished seals or locks that are no longer made
- Glass that is not toughened or laminated in a low-level or door panel where safety glass would now be expected
Replacement Options Explained
- Sealed unit replacement. The glazing beads are removed, the failed unit is taken out and a new unit made to the exact size is fitted. Usually a visit to measure and a short visit to fit.
- Upgraded glass units. A replacement unit can be better than the original, with low-emissivity coating, argon gas fill and warm-edge spacer bars, or with acoustic or laminated glass.
- Hardware and seal repairs. New hinges, locks, handles and gaskets can extend the life of sound frames alongside new glass.
- Whole-window replacement. Where frames are failing, complete new windows are fitted, bringing current energy performance, security and ventilation.
- Phased replacement. Some households replace the worst elevation first and the rest later. Ask whether the same profile and colour will still be available.
What to Include When Asking for a Quote
Say how many glass units have misted or cracked, which windows they are in, and roughly how big each pane is. If there are markings printed in the spacer bar between the panes, such as a manufacturer's name or date, note them down, as they help estimate the age of the installation. Mention whether any of the affected units are in doors, next to doors or low down, because those may need toughened or laminated safety glass.
If you think the frames may also need replacing, describe what else is wrong: whether sashes drop, whether locks are stiff and whether the frames have discoloured. Ask each installer to give a view on whether new units or new windows make more sense, and to explain why. A firm that only sells whole windows and one that only replaces glass may give you very different advice.
A quote for sealed units should give the size, glass make-up and spacer type for each unit and the guarantee on the new units. A quote for whole windows should list each window's style, frame system, energy rating and what is included for removal, cills, boards and making good.
How Much Does Double Glazing Replacement Cost?
| Job size | Typical cost |
|---|---|
| One replacement sealed unit in an existing frame | £150 – £350 |
| Several windows replaced on one elevation | £2,000 – £5,000 |
| Whole house of old double glazing replaced with new windows | £6,000 – £11,000+ |
These are guide figures only. The price of a sealed unit depends on its size, glass type and access. Whole-house prices depend on the number and style of windows, frame material and colour. Always confirm VAT and exclusions.
The Replacement Process
- Assessment. The installer checks whether the frames are worth keeping and measures the glass or the whole openings.
- Ordering. Sealed units are made to the exact size, typically within a week or two; whole windows take longer.
- Glass-only fitting. For unit swaps, beads are removed, the old unit lifted out, the new one packed and re-beaded. Each unit usually takes well under an hour.
- Whole-window fitting. For full replacements, old frames are removed, new ones fixed, glazed and sealed, usually a few windows per day.
- Handover. The installer checks every sash, cleans the glass, removes old units and frames, and provides any certificate needed.
Planning Permission and Building Regulations
Swapping only the glass in an existing frame is generally treated as a repair rather than new window work, so it does not normally need planning permission or a Building Regulations certificate. Replacing the whole window, frame included, is controlled work: the new window must meet current energy efficiency standards, and an installer registered with a competent person scheme such as FENSA or Certass can self-certify it. See the Planning Portal's Building Regulations guidance.
Whole-window replacement on a house is usually permitted development if the new windows look similar. Flats, listed buildings and homes in conservation areas covered by an Article 4 direction may need consent, so check first if any of these apply.
How to Choose a Double Glazing Installer
- Do you replace individual sealed units as well as whole windows?
- In your view, are my frames worth keeping, and why?
- What glass specification will the new units have, and what guarantee comes with them?
- Will safety glass be fitted where the regulations expect it?
- For whole windows, are you registered with FENSA, Certass or another scheme?
- Can you match the colour and profile of my other windows if I replace in stages?
Frequently Asked Questions
Can I replace just the misted glass instead of the whole window?
Yes, if the frame is in good condition. A new sealed unit can be made to fit the existing frame. If the frame is warped, the hinges have failed or the locks no longer work, replacing the whole window is usually better value.
Why does double glazing mist up between the panes?
The seal around the edge of the unit has failed, letting moist air in. The desiccant inside can no longer absorb it, so condensation forms between the panes. Once this happens the unit cannot normally be fixed and needs replacing.
Do I need a FENSA certificate for new glass units?
Replacing only the glass in an existing frame is generally treated as a repair and does not normally need a certificate. Replacing the whole window, including the frame, does need to be certified or approved.
How long does double glazing last?
Sealed units often last 20 years or more, and good frames can last longer. Units in exposed or sunny positions and frames that have not been maintained may fail sooner.