Old windows can contribute immeasurably to the special interest of a building. The timber used historically is superior to that widely available today. Compared to manufacture with modern substitute materials, use of timber is also more environmentally-friendly and facilitates easier repair. Substitutes are rarely as low-maintenance as often supposed – testified, for instance, by the marketing of purpose-made paint for PVCu windows discoloured by sunlight. Additionally, lower long-term costs favour the retention of old timber windows.

Commonly, only a small area is affected, such as the bottom of the window where there is wet rot. A skilled carpenter will in many cases be able to let in well-seasoned matching new timber. For example, a decayed end to a bottom rail might be renewed, complete with tenon, and the joint pegged, re-wedged and glued. A rotten outer section to a cill may be cut back in situ and replaced with new timber held by glue and non-ferrous screws. New timber of low natural durability should be double vacuum treated.

Minor areas of decay can simply be built up with two-pack filler. It is important, of course, to eliminate gutter leaks or other causes of damp.

Where excess paint or wrongly painted parts is causing sticking, an inorganic solvent stripper can help. Where binding results from a distorted frame, carefully planing and sanding should prevent jamming. Severe distortion, may indicate structural problems (wall movement or failed lintel). Where sliding sashes stick, this may indicate the need for general overhaul. Easing should be avoided in damp weather or recently uninhabited buildings, as opening lights will free themselves when environmental conditions change.

Windows post-dating the 18th century are usually of softwood and require regular redecoration for protection. After removal of loose or defective paint, exposed surfaces are rubbed down (using wet abrasion to minimise hazardous dust). Paint selection will depend upon such factors as the historical importance of the building and surviving finishes. Legislation allows the use of lead-based paint, with permission, on certain listed buildings (Grades I and II*, or in Scotland Grade A), although toxicity concerns mean that alternative finishes are often specified today.

Edwardian windows