Watch a video clip about the treatment of timber surfaces.

Advice & Guidance


The style of the windows used in a place of worship can often provide clues about the age of the building and its pattern of development.  Medieval parish churches will often still have simple leaded lights whilst Victorian buildings might have timber or even metal sash or casement windows.  In all cases it is best to try to conserve and repair the existing window components rather than to introduce new components.

Timber windowTimber windows: Sometimes timber sliding sash windows may ‘stick' and be difficult to open. This is usually caused by a build up of paint layers over the years and can be easily remedied. A skilled carpenter or joiner will carefully cut between the sash and frame and gradually work it free. The excess paint layers should then be carefully sanded away and the whole window repainted. Damp weather will also cause timber windows to expand and the sash to stick.

This can be remedied by carefully sanding the sash and rubbing it with candle wax.

Sash cords will also need to be replaced with new waxed-cotton sash cords from time to time. As this requires the window to be dismantled, you will need to seek specialist help.

windowCasement windows will also expand and ‘stick' in damp weather. As with sliding sash windows, this can be remedied by waiting until the timber is thoroughly dry and then carefully sanding down the affected area before re-painting.

Casement windows can also stick if they have excessive layers of paint. Once again, this can be remedied by sanding down the painted area until the casements open and close easily. Care must be taken not to remove too much timber leaving a gap between the casement and the frame.


Action point: Make sure that window can be opened easily so that the building can be ventilated on dry days during the summer months.

Action point: If softwood windows have previously been painted, make sure that the integrity of the surface is maintained. This will probably mean repainting external timberwork every few years.

Find out more about choosing and maintaining paint finishes.

Metal windows: Metal windows were traditionally made from one of three materials: wrought iron, cast iron or mild steel although examples of bronze and copper frames do exist.

Metal windowTheir historical development reflects the advance of technology. Individually forged wrought iron casements with leaded glass panels are found from the mid sixteenth century onwards. Industrially produced cast iron windows began to appear in the mid eighteenth century, often following the pattern of timber sliding sash windows.

In 1856, Sir Henry Bessemer pioneered a new production process for hot rolled steel, leading to a growth in the number of steel mills and a switch to using mild steel for window frames.

Mild steel windows proved extremely popular and were produced extensively from the early twentieth century to the 1970s when aluminium began to take over as the favoured material. Properly maintained, metal windows can last for centuries. However, when protective coatings are neglected corrosion may occur.

Ungalvanised steel windows (generally pre-dating 1950) are the most susceptible to rusting under these circumstances, though wrought and cast iron can also be affected.

Metal windowCorrosion leads to the loss of original material and staining on adjacent surfaces. It may also cause glass to crack and masonry to split at fixing points (‘rust jacking') as the rust occupies up to seven times the volume of unoxidised metal. Other potential problems include the fracturing of cast iron because of impact or casting flaws and the distortion of wrought iron or mild steel following forcible closure of casements where there is excessive paint build-up.

As a rule, metal window frames will need regular painting every three to five years to prolong their lifespan.


Where paint is starting to flake this could indicate a more serious problem of corrosion so check for any signs of rust by probing the affected area using a pointed tool.

If the corrosion is extensive, seek specialist help. If the metal is sound, the flaking paint can be carefully removed by scraping or sanding and the metal can then be primed and prepared for painting with a suitable paint.

Action point: Make sure that opening panels are operable so that the building can be ventilated on dry days during the summer months. Lubricate window ironmongery and check the security of any locks.

Leaded windowsLeaded windows: Although leaded windows are fairly robust it is advisable to check their condition on a regular basis, using binoculars if they are high up.

Check the glass for broken or cracked panes and inspect the cames (the H shaped strips of lead that make up the lead matrix) and wire ties for signs of damage.

If the glass and the lead appear to be buckled and deformed this might indicate that the lead matrix has deteriorated. Report any deformed windows to your architect or surveyor.

Leaded windows often have a panel that pivots horizontally to open inwards allowing the building to be ventilated. These are often called hopper windows and were developed for use in late nineteenth century industrial buildings. They usually have a wire mesh cage to prevent birds getting into the building and a mechanical operating system with a cord.

Over time, they tend to become difficult to use but can be easily cleaned, repaired and brought back into use. This is a worthwhile task as good ventilation is one of the key ways of removing excess water vapour from a building.

Opening hopperAction point: Make sure that opening panels are operable so that the building can be ventilated on dry days during the summer months.

You should also clear away any dirt from condensation drainage channels and holes at the base of windows.


Glass: Historic glass is very important and is increasingly rare. Clear glass is particularly vulnerable as its significance can often go unnoticed, although the imperfections in old glass add greatly to the character of a building.

Stained glass Plain glass

The glass may also be of a type that is irreplaceable now, so cracked panes should not necessarily be discarded. Missing panes of clear glass can be replaced with a modern cylinder glass from a specialist supplier. Whilst perhaps lacking the character of historic glass, this is better than using a perfectly flat modern material. If you have concerns about your glass seek advice from a specialist glazier. This is particularly true for painted and stained glass windows.

Ferramenta: You should also note the condition of the ferramenta (the structural metalwork that supports the glazing). Rusting ferramenta will expand and can cause the surrounding stonework to crack and split, so it is important that they are kept in good condition.

Medieval wrought ironBadly corroded fixings can be dangerous, so check these carefully. Broken sections of wrought iron and steel can be welded whilst small repairs are sometimes carried out using a metal-rich epoxy resin. If you find evidence of rust this will need to be cleaned off before repainting is carried out.

Most metalwork, including cast iron and mild steel, needs the protection of a regular coat of paint, especially if the building is located in a coastal environment. Ferramenta can also be tipped with phosphor bronze to protect the section embedded in the wall from rust.

Ironmongery: Hinges, sash pulls, latches, stays and locks are very important to the character of any historic window and should be repaired and retained if possible. Retaining the original ironmongery will maintain the integrity of the historic window. 

Action point: Lubricate window ironmongery (but not with oil or grease) and check the security of any locks.

Further information

© SPAB 2012