Double glazing is a cornerstone of UK home comfort, designed to keep the heat in and the British weather out. However, when seals fail or glass cracks, your hom...
Repairing a "blown" or damaged window is often significantly cheaper than a full replacement. This guide covers everything from fixing misted units to replacing faulty hinges, helping you restore your windows to peak performance.
What Does the Work Involve?
- Initial Assessment: A specialist inspects the unit to determine if the failure is in the glass, the seal, or the frame mechanism.
- Measurement: For glass replacement, precise measurements of height, width, and unit thickness are taken to ensure a bespoke fit.
- Deglazing: The internal or external beads are carefully removed to extract the damaged Insulated Glass Unit (IGU).
- Cleaning and Prep: The window rebate is cleaned of old debris, and drainage holes are checked for blockages.
- Installation: The new double-glazed unit is positioned using packers to ensure it sits square and operates correctly.
- Finishing: Security beads are snapped back into place, and fresh silicone or gaskets are applied to ensure a watertight finish.
Typical Costs
Prices vary based on the size of the pane, the type of glass (e.g., toughened or Low-E), and your location in the UK. The figures below include VAT and typical labour charges for 2025/26.
| Service Type | Low £ | High £ | Notes |
|---|---|---|---|
| Small Window Pane (Replacement) | £120 | £200 | Standard uPVC casement unit. |
| Large Window / Patio Door Pane | £250 | £550 | Requires toughened safety glass. |
| Replacement Hinges (Pair) | £75 | £130 | Includes labour and parts. |
| Handle Replacement | £60 | £100 | Often cheaper if done with other repairs. |
| Misted Unit "Repair" (Resealing) | £80 | £150 | Note: Usually better to replace the unit. |
Price Factors: Expect to pay more for scaffolding if the window is difficult to reach, or for specialist glass like acoustic laminate or decorative leaded designs.
How Long Does It Take?
- Initial Survey: 20–30 minutes to measure and diagnose the issue.
- Lead Time: 3–7 working days for the bespoke glass unit to be manufactured.
- Standard Pane Replacement: 45–90 minutes per window.
- Hardware Repairs: 30–60 minutes for handles, hinges, or locks.
- Full House Seal Refresh: 1 day for a standard semi-detached property.
DIY or Professional?
While replacing a handle is a straightforward DIY task, glass replacement should be left to the professionals. Handling large glass shards is hazardous, and incorrect measurements by even 1mm can result in a unit that won't fit or will fail prematurely.
Professional installers provide a guarantee (usually 5–10 years) on the seal of the new unit, which you won't get with a DIY attempt.
Choosing the Right Tradesperson
- Check Accreditations: Look for FENSA or CERTASS registered installers, or members of the GGF (Glass and Glazing Federation).
- Warranty: Ensure they offer a minimum 5-year guarantee against "misting" or seal failure.
- Specialism: Some firms specialise in "window surgery" or repairs rather than full replacements—these are often more cost-effective.
- Does the quote include the disposal of the old glass?
- Is the replacement glass "Low-E" (energy efficient) to match modern standards?
- Are you replacing the gaskets or just using silicone?
UK Regulations
- Part L (Conservation of Fuel and Power): Replacement glass must meet minimum thermal performance standards (U-values).
- Part K (Protection from Falling): Safety glass (toughened or laminated) is mandatory for windows in "critical locations," such as doors, low-level windows, or bathrooms.
- FENSA/CERTASS: While simple glass replacement doesn't usually require a building regulations certificate, full frame replacement does.
Common Problems
- Blocked Drainage: If water can't escape the frame through the bottom weep holes, the unit will sit in water and the seal will fail rapidly.
- Cheap Sealants: Using low-grade silicone instead of proper glazing gaskets can lead to leaks and draughts within months.
- Incorrect Packers: If the glass isn't "toed and heeled" correctly using plastic packers, the window sash will drop and catch on the frame.
- Mismatched Glass: Replacing one pane with standard glass when the rest of the house has a slight tint or leaded pattern can look unsightly.
Frequently Asked Questions
Can you fix a misted window without replacing the glass?
While some companies offer to drill holes and "dry out" the unit, this is often a temporary fix. Once the seal is broken, the desiccant inside is saturated. Replacing the entire glass unit is the only long-term solution.
Why is there condensation on the outside of my new windows?
This is actually a sign of high performance. It means the unit is so thermally efficient that the outer pane is cold, causing atmospheric moisture to condense on it, rather than heat escaping from your home.
My window is draughty but the glass is fine. What’s wrong?
This is usually caused by worn hinges (friction stays) or perished rubber gaskets. Replacing these components is inexpensive and will usually pull the window tight against the frame again.
Do I need to replace the whole frame if the glass is cracked?
No. Double-glazed units are designed to be replaced independently of the uPVC, timber, or aluminium frames, provided the frame itself is still structurally sound.
How can I tell if my double glazing has "blown"?
Look for fogging, misting, or water droplets between the two panes of glass. If you can't wipe it off from either the inside or the outside, the internal seal has failed.
This guide was written with AI assistance and is intended for general information only. Prices are estimates based on UK averages and may vary by region. Always get at least three quotes and consult a qualified professional before starting any work.
