Windows

The Crittall metal-framed window became the most popular form of window, and was particularly used to create swept curves on houses and flats. These were often referred to as 'suntrap windows'. They are single-glazed, and many have now been removed because their thermal performance does not match modern expectations; the amount of condensation produced on the glazing is often regarded as undesirable. The use of heavy curtains at the time helped to keep this to a minimum, and the refitting of similar curtains can be an effective way to control condensation.

Up to the 1950s, metal windows were coated using a cold-dip method in which red lead paint was applied. The removal of this material is a respiration hazard. Later the protection was improved by using hot-dipped zinc. The bottom rail or 'cill' is liable to rust first as it is more vulnerable than the jamb and head.

Over-painting can make casements hard to open, and the security of the casement catches is not easy to upgrade satisfactorily. It is possible to obtain modern replacement metal-framed windows, but the original slimline effect of the glazing bars is difficult to replicate if double glazing is introduced. When considering modern replacements, the general air leakage of the originals must be compensated for with controlled ventilation facilities.

Rusty windows from the 1920s and 1940s can be renovated once removed. Once the glazing has been taken out, the paint and rust can be cleared from the surface with acid or gentle grit-blasting (wire brushes or angle grinders must not be used to do this). Sections may be repaired by cutting out the corroded section and welding in a replacement.

Red lead primer can be reused, but it is highly toxic. A suitable alternative is a flame-sprayed zinc primer to BS 5493, which is an excellent pre-paint treatment for ferrous metals. For steel windows, long-term corrosion resistance can be achieved most effectively by hot-dip galvanising.