How Long Do Double-Glazed Windows Last?

Most double-glazed windows last 20–25 years — but that number hides a lot of variation. Here's what actually determines how long your windows will last and what to watch for as they age.

The short answer: 20–25 years is the standard

A well-made, properly installed double-glazed window should give you at least 20 years of reliable performance before you start seeing significant problems. Many will last longer. Some — particularly those installed by cheaper fitters or in very exposed locations — will start to show issues sooner.

If your windows were installed in the mid-2000s or earlier, they're at the age where you should start paying attention to how they're performing.

What fails first — the glass or the frame?

Usually the glass unit. The sealed unit (the double-glazed glass pane itself) is the component most likely to fail first, because the gas-tight seal degrades over time. When the seal fails, moisture gets in between the panes — this is the cause of the misty or condensation-streaked appearance that's the most visible sign of failure.

The good news: a failed sealed unit doesn't mean you need a new window. In most cases you only need the glass unit replaced, not the frame. Glass replacement starts from £165 + VAT and is far cheaper than a full window replacement.

The frame itself — uPVC or aluminium — is more durable. A good uPVC frame can last 30+ years if it's not been physically damaged.

What affects how long windows last?

Orientation and sun exposure

South-facing windows take the most sun. More sun means more heating and cooling cycles, which causes more expansion and contraction of the frame and seals. This gradually stresses the sealed unit seal, and south-facing windows often fail 3–5 years earlier than north-facing windows on the same house.

Installation quality

A poorly fitted window — wrong-sized glass unit, inadequate beading, missing drainage slots — will fail faster. Sealed unit seal failures that appear within 5–10 years of installation are often down to installation rather than product quality.

Coastal and exposed locations

Properties in exposed positions — coastal, hilltop, or wind-facing elevations — experience more stress on window seals and frames. If you're in Portishead or similar exposed locations, your windows may age faster than the Bristol average.

Product quality

There's a significant quality range in uPVC windows. Budget frames use thinner profiles and cheaper hardware. Better frames use multi-chambered profiles, high-quality hardware, and better-sealed units. The difference in longevity can be 5–10 years.

Signs your windows are failing

• Condensation or misting between the panes — the sealed unit seal has failed
• Draughts when closed — the frame seal or weather-stripping has degraded
• Handles that won't turn smoothly — mechanism wear, very common after 15+ years
• Hinges that are stiff or causing the window to drop — hinge wear
• Difficulty opening or closing — often frame distortion or hinge problems
• Visible discolouration or yellowing of the frame — UV degradation of older uPVC

Repair or replace?

Not everything that goes wrong with an ageing window means it needs replacing. A misted unit needs the glass replaced — not the whole window. A stiff handle or failed hinge needs repairing, not a replacement frame.

The cases where full window replacement makes sense:

• Multiple things are failing at once on an old frame
• The frame itself is cracked, warped, or letting in draughts that can't be fixed with new seals
• The windows are original 1990s units that have never been touched and are now 25–30 years old
• You want to upgrade to a higher-spec frame for better insulation or appearance

We'll always give you an honest assessment. If a repair will do the job, we'll say so.