Repair or Change Windows in an Older Home

Properly maintained, historic timber windows can last indefinitely as they were usually made of high-quality durable timber. 

Use the best methods and materials

There is a widely held view that repairs are short lived and not as good as new replacement windows. This need not be the case if you use an experienced joiner and the right materials, even for external softwood frames. It is the poorly thought-out repairs, or ones using unsuitable materials, that will quickly fail.

Do the minimum

Limit any work to the minimum required to fix the problem.

Do the work on site

Wherever possible, repairs to window frames should be carried out on site, particularly when the frame is built-in and cannot be easily removed without damaging either the window or the surrounding wall.

Window sashes

The individual sashes from sash windows and casement windows can usually be removed for repair without damage.

Keep track of components

If several windows have to be dismantled in the course of repair, mark and record all the components and where they fit in before beginning the work as there are bound to be tiny variations.

Metal windows can suffer from surface rust, distortion, excessive build-up of paint or failed hinges and fittings. They can often be economically repaired and draught-proofed, avoiding the need to replace them.

Rust does not mean replacement is necessary

• Rust expands up to seven times the volume of sound metal, so corrosion often looks much worse than it really is.
• Heavy rust and paint can be removed by acid pickling or flame cleaning. There are several firms specialising in this kind of work.
• Renovation can be done on site, using wire brushes, files, and small grinders to remove rust and scales. Or the work can be done in a factory, where the windows can be grit- or shot-blasted and galvanised or zinc-sprayed.

Type of metal matters

The best way of repairing a metal window will depend on the type of metal it is made of:

• Ferrous metals will have different problems to non-ferrous metals such as bronze and aluminium, and within the ferrous metals wrought iron will need to be treated quite differently to cast iron or steel
• Any necessary repairs to wrought iron or steel windows can be made by a metalworker welding in replacement sections
• Cast-iron windows cannot be welded because they tend to crack when heated, but they can be repaired using a technique known as 'cold stitching'

The manner of production is also important: for example, early steel windows (before the mid-1950s) were not galvanised and so are particularly prone to corrosion, which often appears as rusting of the horizontal glazing bars and the bottom rails.

Read more about conservation of metal windows: Historic steel-framed windows in volume 162 of 'Context', the Journal of the Institute of Historic Building Conservation, published by Cathedral Communications Ltd in November 2019.

For more information on repairs to windows see our guidance below:

Making sure that windows and frames fit well reduces draughts and heat loss, so does adding draught-stripping.

Our research into different ways of making windows more energy efficient revealed that you can significantly reduce heat loss by using any of the following:

• Window shutters
• Insulated blinds
• Thick curtains

If you have window shutters, close them at night. If your shutters are missing, consider having new ones made. 

More on draught-proofing windows and doors

To further reduce heat lost through windows and match the performance of new windows, consider installing secondary glazing.

This retains your existing historic windows and, if designed carefully, will preserve the importance of the external and internal appearance of your building. Make sure the design of the secondary glazing is compatible with any existing window shutters, panelling or mouldings.

It’s important that where you install secondary glazing, you prevent condensation and mould developing by not draught-proofing the original window.

More about secondary glazing

Double or triple glazed windows have multiple panes of glass, designed to reduce heat loss and noise. They have a lower life expectancy than single glazed windows however, needing replacing roughly every 30 years compared to 60 to 100 years for single glazed windows.

It may be possible to fit slim-profile or vacuum sealed double-glazing units into historic buildings.

This can be considered where window frames of special interest are kept, where no important glass remains, and where increased glazing unit size and weight can be accommodated. Careful consideration should be given to any physical changes required to do so.

Where windows that do not contribute to special interest are to be replaced, double-glazed windows with an appropriate material and pattern could be considered.

However, we still recommend secondary glazing as the preferred option. Research has shown that:

Secondary glazing can reduce heat loss by over 60%

Secondary glazing has lower environmental impact than double or triple glazing

Although PVCu (unplasticised polyvinyl chloride) rigid plastic replacement windows are popular, there are good reasons for not replacing older windows with them.

Appearance

Their appearance can have a negative impact on older buildings. Because the components used to manufacture PVCu windows are weaker than their timber counterparts, they tend to be much thicker. They also have different detailing and opening arrangements. For example, in traditional windows the glazing bars (usually wooden or metal) are rigid and separate the panes of glass, whereas in PVCu windows they are often only strips of plastic inserted within the glass sandwich of a double-glazed unit.

They don't last as long

The service life of PVCu windows is relatively short (less than 25 years) compared to well-maintained traditional windows (many of which survive for over 100 years).

Difficult to maintain and repair

PVCu windows are not maintenance-free and can be difficult to repair. As a result, they are usually replaced at the end of their service life. Although it is possible to recycle PVCu, this is still not done widely.

Higher environmental impact

A PVCu replacement window will have a higher environmental impact than a traditional window that's been upgraded to improve its energy efficiency.

Effective insulation of dormer windows can be tricky. Every junction and gap needs to be carefully insulated. If dormer windows are not insulated or the insulation is poorly detailed, they can impact the energy performance of the whole roof. Ideally, the upgrading of dormer windows should be done together with general roof upgrading work.

More about insulating dormer windows 

Dormer windows can be a very prominent feature on many historic buildings. Avoid making changes that affect their proportions or external features if you are upgrading one. This is even more important if the design of the window reflects that of other windows on your building or neighbouring buildings.

For listed buildings and those in conservation areas, talk to your local planning authority before adding insulation to dormers, particularly if there are likely to be any changes in appearance.