Window replacement in historic buildings

It is usually impossible to install double-glazed units in existing frames without altering the character or appearance of a listed building. Listed building consent is quite likely to be refused for such an alteration because the form and detailing of windows is so often a key architectural element of historic buildings. The more complicated the glazing pattern the more difficult it will be to double glaze and for the installation to meet acceptable conservation standards. Conversely, where there is a simple undivided single sheet of glass in each frame double glazing can usually be fitted without any appreciable change to the appearance and character of the window.