Owning a listed building is a privilege — but the rules around windows can be frustrating. Listed-building consent typically prohibits replacement of original windows even where they're draughty, single-glazed and acoustic nightmares. Secondary glazing offers a heritage-compliant route to modern thermal and acoustic performance without altering the original fabric.
Why listed buildings restrict window replacement
The character of a listed building lies as much in its windows as in its façade — proportions, glazing bar profiles, original glass with its imperfections, and craftsmanship details. Replacement uPVC or modern timber windows almost always damage that character. Conservation officers therefore start from a default of 'no' on replacement, and applications often take 12+ weeks to negotiate.
How secondary glazing sidesteps the problem
Secondary glazing is installed entirely from inside the property, behind the original window. It doesn't touch the original fabric — original sashes, glass and frames remain intact. From outside, the property is unchanged. This means secondary glazing is usually permitted without listed-building consent, and conservation officers actively recommend it as the best heritage-compliant retrofit option.
Performance you'd expect from new windows
Modern slimline aluminium secondary glazing with Low-E glass achieves U-values around 1.8 W/m²K — comparable to standard new double glazing. With acoustic laminated glass and 100mm+ air gap from the primary window, noise reduction reaches 45-50 dB — better than most new double glazed windows.
Operation and ventilation
Our secondary units have hinged, vertically sliding or lift-out openings — you can still operate the original window for ventilation and cleaning. Trickle vents and acoustic baffles maintain background ventilation as required by building regulations.
What it costs
Bespoke secondary glazing typically costs £450-£800 per window installed depending on size, glass specification and frame finish. Considerably less than the conservation-grade replacement timber sashes that might otherwise be required, and faster to install (typically a single day for a whole house).
Specifying for your property
We've installed secondary glazing in Grade I and II listed buildings across the UK including Georgian terraces, Victorian villas, Regency seafront properties and 17th century farmhouses. Each installation is bespoke to the property. Call 0800 088 6341 for a heritage consultation.
Need help with your glazing project? S&K Glazing offers free surveys and fixed-price quotes across the UK. Call 0800 088 6341, message us on WhatsApp at 07830 175306, or request a quote online.