Double Glazing Repairs London: Glass Replacement or New Windows?

If your double-glazed window has misted glass, a crack, draughts or a damaged frame, you may be wondering whether you need a complete replacement. The answer depends on which component has failed. In many cases, replacing the sealed glass unit or repairing the window hardware can be a practical alternative.

What This Guide Covers

• Misted glass means the sealed unit has failed — not the frame. Replace the glass unit, not the whole window.
• Cracked or broken glass must be replaced promptly; the frame can usually be retained
• Draughts are often caused by alignment or seal faults — not glass failure
• Full window replacement is appropriate when the frame is damaged, distorted or uneconomical to repair
• Always compare the complete cost of repair versus replacement before deciding

Introduction

London homeowners face unique challenges when it comes to glazing — from period properties with sash windows in conservation areas, to modern developments requiring structural glass installations. Getting the right advice before you commit can save you significant time and money.

At BuilderFix Glazing, we have completed thousands of glazing jobs across Greater London and Surrey — from emergency repairs in Kensington and Chelsea, to bespoke walk-on glass installations in Mayfair and Belgravia. This guide is based on real experience and the questions our customers ask us most often.

In Depth

The most important thing to understand about double-glazed windows is that the glass and the frame are separate components. When something goes wrong, the question is which component has failed — and in most cases, it is only one of them. A sealed unit that has misted does not mean the frame is defective. A frame that has dropped does not mean the glass needs replacing. Correctly identifying the fault is the difference between a £100 repair and an unnecessary £600 replacement.

Misted glass is the most common reason homeowners in London contact us about double-glazed windows. The cloudy or fogged appearance between the panes is caused by moisture entering the sealed unit after the perimeter seal has failed. This is a glass unit failure, not a frame failure. The solution is to remove the failed unit and install a correctly specified replacement — same dimensions, same thickness, same glass type. In most cases this takes under two hours and the existing frame is untouched.

Cracked or broken glass is a different category of problem. Broken glass needs prompt attention for both safety and security reasons. In most cases the frame is undamaged, and only the glass unit needs to be replaced. However, the replacement specification matters. Safety glass — toughened or laminated — is required in certain locations under Building Regulations, including low-level panes, glazed doors, side panels and bathroom windows. A glazier fitting an annealed unit in a location that requires safety glass is creating a compliance problem.

Draughts and water ingress around a double-glazed window are frequently misdiagnosed as glass failures. Cold air entering around the frame is almost always a hardware or alignment issue — worn seals, misaligned hinges or a dropped sash that no longer compresses against its weather seal. Replacing the glass unit will not fix a draught caused by a 3mm gap between the sash and the seal. The correct repair is identifying the source of the gap and addressing it.

Full window replacement becomes the right answer when the frame is genuinely failing — visible distortion, cracked welded corners, rotting timber, or a frame that cannot be adjusted back into alignment. It is also appropriate when the cost of multiple component repairs approaches the cost of a new window, particularly in older frames where hardware may be unavailable. BuilderFix will always give an honest assessment of which route makes more sense for your window.

What Does This Typically Cost in London?

Costs vary depending on the type and size of work, the glass specification, frame material, and access. As a general guide, always obtain a free written quote before committing — this protects you from unexpected charges.

At BuilderFix Glazing, we provide free, no-obligation written quotes for all work. Our prices are transparent and fixed before we start — no surprises on the invoice.

What to Ask When Getting a Quote

• Is the price fixed, or could it change once work starts?
• What glass specification is included?
• Are all fixings, sealants and finishing included?
• What compliance documentation will I receive?
• What happens if there is an issue after completion?