How Long Does Double Glazing Last? Signs It's Time to Replace

Double glazing is one of those home improvements that most people install and then forget about — until something goes wrong. The good news is that modern double-glazed windows are designed to last decades. The bad news is that nothing lasts forever, and there are clear warning signs that your windows are approaching the end of their useful life.

This guide covers the realistic lifespan of double glazing in UK conditions, the telltale signs of failure, when repair makes more sense than replacement, and what you can expect to pay for new windows in 2026.

How Long Does Double Glazing Actually Last?

The honest answer is that it depends on the quality of the original installation, the materials used and how exposed the windows are to the elements. Here are realistic lifespans for different types of double glazing:

uPVC Double Glazing

• Budget uPVC (1990s-2000s era): 15-20 years
• Mid-range uPVC: 20-25 years
• Premium uPVC (e.g., Rehau): 25-35 years

The uPVC frame itself can last 35-40 years, but the sealed glass units — the part that actually provides insulation — typically last 20-25 years before the seals begin to degrade. When you see condensation between the panes, that is a failed seal, and the insulating gas fill has escaped.

Aluminium Double Glazing

• Standard aluminium: 30-40 years
• Premium thermally broken aluminium (e.g., Cortizo, Schuco): 40-50+ years

Aluminium frames are significantly more durable than uPVC. They do not expand and contract as much with temperature changes, they do not discolour, and they do not warp. Premium systems from brands like Cortizo and Schuco are genuinely expected to last the lifetime of the building.

Timber Double Glazing

• Softwood (painted): 20-30 years with regular maintenance
• Hardwood (e.g., oak, iroko): 40-60+ years with maintenance

Timber windows can last the longest of all, but only if they are properly maintained. Without regular repainting and sealing — every 3-5 years for softwood — timber windows can deteriorate rapidly, with rot setting in within 10-15 years.

The Sealed Unit: The Weakest Link

Regardless of the frame material, the sealed glass unit (also called an insulated glass unit or IGU) is the component most likely to fail first. A sealed unit consists of two panes of glass separated by a spacer bar, with the cavity filled with an insulating gas (usually argon) and sealed around the perimeter with a desiccant-filled spacer and sealant.

Over time, the edge seals degrade — accelerated by UV exposure, thermal cycling and moisture. When the seal fails, moisture enters the cavity and the insulating gas escapes. The result is condensation between the panes that you cannot wipe away, and a significant reduction in thermal performance.

The typical lifespan of a sealed unit is 15-25 years, though some premium units with warm-edge spacer bars and improved sealants can last 30 years or more. Importantly, a failed sealed unit does not mean you need to replace the entire window — often just the glass unit can be swapped out, keeping the existing frame in place.

Seven Signs Your Double Glazing Needs Replacing

1. Condensation Between the Panes

This is the most obvious sign of seal failure. If you can see misting, fogging or water droplets between the two panes of glass — not on the inside surface or the outside surface — the sealed unit has failed. The window is no longer providing effective insulation.

2. Draughts Around the Frame

If you can feel cold air coming through or around closed windows, the seals, gaskets or weatherstripping have deteriorated. In some cases, the frame itself may have warped. Stand next to your windows on a cold, windy day and hold your hand near the edges — draughts are surprisingly easy to detect.

3. Difficulty Opening or Closing

Windows that stick, jam or will not close properly are more than an inconvenience — they are a security risk. The causes include frame distortion from thermal cycling, failed hinges, broken locking mechanisms or foundation settlement causing the frame to rack. If multiple windows are affected, it usually points to a systemic issue rather than individual component failure.

4. Visible Frame Damage

Cracks, warping, discolouration (particularly yellowing of white uPVC), or soft spots in timber frames all indicate structural degradation. Minor surface issues can sometimes be repaired, but significant warping or cracking usually means replacement.

5. Excessive External Noise

If you live near a busy road and your windows no longer seem to block traffic noise effectively, the sealed units may have lost their gas fill. Modern double glazing with intact argon fill reduces external noise by 25-35 decibels — if your windows no longer achieve this, they have likely degraded.

6. High Energy Bills

Old or failing double glazing lets significantly more heat escape than modern equivalents. If your energy bills have been creeping up despite no change in heating habits, inefficient windows could be a major contributor. A house with windows from the 1990s can be losing 20-30% more heat through the glazing compared to modern A-rated equivalents.

7. Visible Rot (Timber Windows)

For timber windows, any sign of rot — soft wood when prodded with a screwdriver, flaking paint, or dark discolouration at joints — requires urgent attention. Surface rot can sometimes be repaired with wood hardener and filler, but structural rot in the frame joints means replacement is the only reliable solution.

Repair vs Replace: When Does Each Make Sense?

When Repair Makes Sense

• Failed sealed units on sound frames: Replacing the glass unit alone costs £50-£150 per window vs £300-£800 for a full window replacement
• Faulty hinges or handles: A straightforward hardware swap costing £30-£80 per window
• Worn gaskets and weatherstripping: Can be replaced for £10-£30 per window to restore draught-proofing
• Minor timber rot: Surface rot can be cut out, treated and filled if the frame is structurally sound

When Replacement Is the Right Call

• Multiple failed sealed units: If more than half your windows have failed seals, it is more cost-effective to replace the lot
• Warped or cracked frames: No amount of repair will restore a structurally compromised frame
• Windows over 20 years old: Even if they appear functional, old windows are significantly less efficient than modern equivalents. The energy savings alone can justify replacement within 8-12 years
• Security concerns: Old locking mechanisms do not meet current security standards. Modern windows with multi-point locking systems offer dramatically better protection
• Aesthetic upgrade: If you are renovating or selling, new windows transform the look of a property and add measurable value

What Do Replacement Windows Cost in 2026?

Costs vary by material, style and size. Here are realistic installed prices for standard-sized windows in the UK as of 2026:

| Window Type | Cost Per Window (Installed) | |-------------|---------------------------| | uPVC casement | £350-£650 | | uPVC sliding sash | £650-£1,100 | | Aluminium casement | £600-£1,100 | | Aluminium flush casement | £700-£1,200 | | Timber casement | £800-£1,400 |

For a typical 3-bedroom semi-detached house with 8-10 windows, expect to pay:

• Full uPVC replacement: £4,000-£7,000
• Full aluminium replacement: £7,000-£12,000
• Mixed (aluminium front, uPVC rear): £5,500-£9,000

These prices include installation, VAT, Building Regulations compliance and a FENSA certificate. Government grants may be available if you meet the eligibility criteria for the ECO4 scheme.

How to Make New Double Glazing Last Longer

Once you have invested in new windows, these steps will help maximise their lifespan:

• Clean the drainage slots: Every window has small drainage holes in the bottom rail. Keep them clear of dirt and debris so water can drain away from the sealed unit edge
• Lubricate hinges and locks: A drop of light machine oil on hinges and lock mechanisms once a year prevents premature wear
• Clean rubber seals: Wipe the rubber gaskets with a damp cloth twice a year. Do not use solvent-based cleaners as they degrade rubber
• Open windows regularly: Even in winter, opening windows periodically prevents moisture build-up that can accelerate seal degradation
• Repaint timber windows on schedule: Every 3-5 years for softwood, every 5-8 years for hardwood. Do not wait until the paint is visibly failing

How Vitrum Solutions Can Help

We supply and install uPVC windows from Rehau, aluminium windows from Cortizo and Schuco and a range of entrance doors across Buckinghamshire, West London and the surrounding areas. Every installation comes with a 10-year insurance-backed guarantee, a FENSA certificate and a commitment to zero-fuss aftercare.

If you are unsure whether your windows need replacing or just repairing, we offer free, no-obligation assessments. Call us on 0800 861 1450 or request a quote online.

Frequently Asked Questions

Can I just replace the glass and keep the frames?

Yes, if the frames are in good condition. Replacing sealed glass units is significantly cheaper than full window replacement — typically £50-£150 per unit compared to £350-£800 for a full window. However, if the frames are more than 20 years old, you may find that new sealed units fail prematurely because the frame can no longer hold them securely.

Is it worth replacing 15-year-old double glazing?

It depends on the condition. If the sealed units are intact, the frames are sound, and the windows operate smoothly, 15-year-old double glazing still has useful life left. However, modern A-rated windows are significantly more thermally efficient, so if energy performance matters to you, replacement can be justified on energy savings alone — typically £100-£200 per year for a full house.

How do I know if condensation is a sign of failure?

Condensation on the inside surface of the glass is normal in cold weather and indicates high indoor humidity, not window failure. Condensation on the outside is actually a sign of good thermal performance. Condensation between the two panes — which you cannot wipe from either side — is the sign of a failed seal and means the unit needs replacing.

Do I need planning permission to replace double glazing?

In most cases, no. Replacing windows on a like-for-like basis is permitted development. However, if you live in a conservation area, a listed building, or an Article 4 direction area, you may need planning permission — particularly if changing the style, material or colour of the windows. Building Regulations approval (via FENSA or local authority) is always required.

Will new double glazing add value to my property?

Yes. Estate agents consistently report that new windows are one of the most cost-effective improvements for adding value. The Energy Saving Trust estimates that upgrading from single to double glazing adds approximately £5,000-£10,000 to the value of a typical UK home. Even replacing old double glazing with modern equivalents improves the EPC rating, which is increasingly important to buyers and mortgage lenders.