Bespoke Timber Windows for Listed Buildings

A listed window is judged by millimetres. The width of a glazing bar, the depth of a moulding and the line where the glass meets the frame are what a conservation officer looks at, and what makes the difference between a window that belongs and one that looks bought in.

This guide covers the joinery side of a listed project: what gets copied from the existing windows, how the new units are made, and the choices you will be asked to make.

Copying the originals

The starting point is a surviving original window, or the best example left on the house. From it the joiner takes the sash section, the bar profile, the horn shape on sliding sashes and the meeting rail detail. Those profiles are drawn at full size and form part of the consent application.

Glazing bars and sightlines

Glazing bars, also called astragals, are the detail officers scrutinise most. On listed work we aim for bars that match the original width and moulding. With slim double glazed units, bars are bonded to both faces of the glass with a spacer between, so the grid reads as true divided lights from inside and out.

• Bar width and moulding copied from the original
• Like for like sightlines on frame, sash and meeting rails
• Putty line or slim bead rather than a deep square bead
• Horns, cills and heads matched on sliding sashes

Timber and finish

Engineered European Redwood is our usual choice, stable and well suited to paint, with Accoya used where exposure justifies it. Finishes are factory applied microporous paints in traditional colours, commonly off whites, heritage greens and greys, agreed with the officer where consent requires it.

Lead times

Bespoke listed units are made to order after consent is granted and typically take eight to twelve weeks to manufacture. Commercial and larger listed buildings follow the same specification process with more openings to survey.

Why this matters beyond consent

Getting the joinery right protects the value of the house. Listed homes are bought for their character, and badly proportioned replacement windows are one of the first things a buyer's surveyor or a future officer will notice.

What you will be asked to decide

Even with the originals as a guide, a few choices fall to the owner: the paint colour where the officer allows a range, the ironmongery finish, whether trickle ventilation is wanted and how it is concealed, and whether slim double glazing or single glazing is used where both would be accepted. We bring samples of bars, mouldings and colours to the house so these are settled in daylight against the real walls rather than from a catalogue.

Questions people ask