Windows and doors are often the most important visual aspect of a building, particularly if they have survived for generations, showing distinctive mouldings, uneven putty glazing and characterful glass.
Upgrading original windows is a sensitive task, as there is an inherent conflict between keeping the character of the original and improving levels of thermal efficiency. When replacement is appropriate, a number of WWA members can provide authentic heritage window designs.
Replication of original window designs
Consent for listed buildings is typically granted on a ‘like for like’ basis, unless the applicant is able to satisfy certain conditions, such as ‘that the building is not of special architectural or historical interest’ – more likely with a Grade II than a higher listing. If repair is not possible, the replacement details will need to replicate the existing design details, including mouldings, glazing method and use of historic glass.
Those WWA members who offer heritage windows offer a variety of mouldings to mimic original windows, including Lamb’s Tongue, Gothic, Ovolo and Bevelled. Casement Windows can incorporate butt hinges and casement stays, whilst vertical sliding sash windows will be the traditional box window design, using cords, weights and pulleys to counter balance the sashes in the traditional way.
Both casement windows and sliding sash windows can incorporate astragal bars (i.e. non-structural applied glazing bars) to mimic the original glazing bars, with some members even offering structural glazing bars when stringent planning demands it. However, all of our members agree that period replica astragal bars (i.e. no structural bars) are much more energy efficient.
The energy efficiency of heritage windows
Narrow cavity insulated glazing units are often used as a compromise between energy-efficiency and authenticity. They incorporate a cavity of 8mm or less and feature reduced spacer-bar sightlines. Where possible, it is preferable to use standard cavity insulated glazing units which are better value, have a longer life and are more energy-efficient. For further detail on narrow cavity insulated glazing, click here to download our Advice Note.