Window Woman guides
Glass options for listed buildings
Old glass is part of a building's character, and the way you improve warmth and comfort matters just as much as the window itself.
Historic glass
- Crown glass: spun into a disc, with a gentle curve and ripple. Used until the mid-19th century.
- Cylinder (sheet) glass: blown as a cylinder and opened flat, with a subtle, uneven reflection.
- Modern float glass: perfectly flat, which can make a historic façade look lifeless.
Old glass is irreplaceable. If any survives, it should be kept, even when the window around it is repaired or remade. Reproduction cylinder glass is available for new work.
Improving warmth and comfort
- Secondary glazing: a discreet internal panel that is fully reversible. Often the most acceptable option in listed buildings, and good for reducing noise too.
- Slimline double glazing: much thinner sealed units that can sometimes be fitted into slender historic sections.
- Vacuum glazing: thinner still, with excellent thermal performance.
- Shutters, blinds and heavy curtains: the original insulation, and still very effective.
Attitudes to slimline and vacuum glazing have softened in recent years, particularly where the existing windows are later replacements. Every case is still judged on its own merits, so never assume approval. The FAQ covers double glazing in more detail.
Worth knowing
- Draughts, not glass, are often the biggest source of heat loss in old windows
- Draught-proofing is usually the best first step
- Glass in doors and low-level panes may need to be safety glass
More guides
These guides are general information for England and don't replace advice specific to your property or your local planning authority.