New Windows vs Window Repair: When to Replace and When to Fix

Start by assessing the frames: press a screwdriver into the timber at the corners and bottom rail. If it sinks in more than 3-4mm, rot is present. Check whether windows close and lock properly, look for condensation between double glazed panes (indicating seal failure), and feel for draughts around the edges. If issues are isolated to specific components and the frames are sound, repair is likely sufficient. If problems are widespread, replacement is more economical.

Yes. Misted sealed units can be replaced independently of the frame. A glazier removes the beading, takes out the failed unit, and fits a new sealed unit into the existing frame. This costs £75-£150 per pane compared to £350-£2,800 for a whole new window. The repair is straightforward for most window types and takes 30-60 minutes per unit.

It depends on the condition. uPVC frames rarely rot but can become brittle, discoloured, or warped over time. If the frames are still white (not yellowed), the welds are intact, and the issue is limited to failed hardware or misted units, repair is worthwhile. If the frames are discoloured, the welds are cracking, or the profiles look dated, replacement will deliver better long-term value.

The Energy Saving Trust estimates that replacing single glazing with double glazing saves £100-£200 per year on heating bills for a typical semi-detached house. Upgrading from old double glazing (1990s era) to modern A-rated units saves approximately £50-£100 per year. These figures vary based on house size, heating system, and energy prices, but provide a reasonable guide for cost-benefit calculations.

Yes. Replacement windows must comply with Part L of the Building Regulations (thermal performance). The easiest way to achieve this is to use an installer registered with a competent person scheme such as FENSA or CERTASS, who can self-certify compliance. If you use a non-registered installer, you will need to apply for Building Regulations approval from your local council, which involves an inspection and additional fees.

Minor surface rot can be addressed by DIY enthusiasts using a wood hardener and epoxy filler system. However, deep structural rot — particularly at joints and the bottom rail — requires timber splicing skills and specialist knowledge. Poorly executed rot repairs can trap moisture and accelerate further decay. For anything beyond surface-level damage, we recommend using a specialist timber window repair company.

It depends on the repair type. Replacement sealed units typically last 15-20 years. New hardware (hinges, locks, handles) lasts 10-20 years. Sash cord replacements last 15-25 years. Timber splice repairs, if properly executed with preservative-treated timber and quality filler, can last 15-20 years. Draught-proofing seals typically need replacing every 8-12 years.

If your windows have minor cosmetic issues, repair is usually sufficient — buyers are unlikely to pay a premium that covers the cost of full replacement. However, if windows are visibly failing (misted, draughty, rotten), new windows can significantly improve kerb appeal and EPC rating. A higher EPC band can add perceived value, particularly as energy efficiency becomes more important to buyers.

Sash windows are highly repairable. Common repairs include sash cord replacement, draught-proofing with brush or compression seals, spiral balance fitting (to replace weights and allow the weight pockets to be insulated), timber splicing for rotten sections, glass replacement, new sash lifts and locks, and rebalancing for smooth operation. A full sash window overhaul typically costs £300-£500 per window.

Secondary glazing — fitting a discreet internal glazing panel behind the existing window — is an excellent compromise in conservation areas where replacement is not permitted. It can improve thermal performance by 60-65% and reduce noise by up to 80%. Costs range from £200-£600 per window, making it cheaper than replacement while preserving the original windows. It is also reversible, which appeals to heritage conservation officers.