A well-made timber window can last 60-80 years or more — but only with proper maintenance. London’s mix of rain, pollution and temperature swings is hard on exterior joinery, and the single biggest cause of premature window failure isn’t the timber itself, it’s a paint or putty line that was left to fail for a season too long. Here’s what actually needs doing, and how often.

Why Timber Windows Fail Early — And It’s Rarely the Wood

Modern timber windows, especially sash windows and casement windows built from engineered or properly seasoned hardwood, are far more resilient than people assume. What actually causes rot and swelling is water getting past a cracked paint film or failed putty joint and sitting in the joint long enough to soften the fibres. Catch that early and a window lasts decades. Miss it for two or three winters and you’re looking at a full sash or cill replacement.

A Realistic Maintenance Schedule

• Every 6 months: Check for flaking paint, cracked putty lines, and sticking sashes. A five-minute visual check from outside catches most problems before they start.
• Annually: Clean and lubricate hardware — hinges, sash cords, pulleys and locks. Clear weep holes and drainage channels of debris so water doesn’t pool.
• Every 4-6 years: Repaint. This is the single most important interval on the list. A quality exterior paint system (primer, undercoat, two topcoats) genuinely protects for 5+ years in London conditions — cheap or single-coat jobs fail in 2-3.
• Every 10-15 years: Re-putty any glazing that shows cracking, and check cills and joints for early signs of rot that can be spot-repaired rather than replaced.

Repainting: What Actually Matters

Most repainting failures come down to preparation, not paint choice. Painting over existing flaking layers, skipping a proper sand-back, or painting in damp conditions will fail within a year or two regardless of how good the paint is. Proper preparation means: strip back to sound timber where paint has failed, treat any exposed bare wood with a suitable primer immediately (don’t leave it exposed overnight), fill with an exterior-grade filler where needed, and apply in dry, moderate-temperature conditions — not in direct summer sun or when rain is forecast within 24 hours.

Signs You’ve Left It Too Long

• Timber that feels soft or spongy when pressed with a thumbnail, particularly at the bottom rail or cill
• Paint that’s bubbled or lifted away from the wood rather than just faded
• Sashes that have become difficult to open, which can indicate swelling from moisture ingress
• Visible daylight or draughts around the frame that weren’t there before (see our guide to draught-proofing sash windows)
• Black staining or soft, crumbling wood — active rot that needs professional assessment

If you’re seeing any of the last two, it’s worth getting a professional assessment before deciding between repair and replacement — localised rot in a cill or bottom rail can often be cut out and spliced rather than requiring a whole new window.

Maintain or Replace?

As a rough guide: if the frame and sashes are structurally sound and the issues are limited to paintwork, putty or hardware, maintenance is almost always the cheaper and more sustainable option — and it’s what keeps a period property’s original joinery intact, which matters for both character and, in conservation areas, for planning compliance. If you’re dealing with structural rot across multiple sashes, failed double glazing units, or windows that were poorly installed to begin with, replacement with properly specified bespoke timber windows is usually the better long-term investment. See our guide to timber sash window costs for realistic replacement pricing if you’re weighing the two options.

How International Windows Group Can Help

Beyond supplying and installing new timber windows and doors across London, we can assess existing joinery and advise honestly on whether repair or replacement makes more sense for your property. Get in touch for a free assessment.