Why the CSG System Stands Out From Other Secondary Glazing Systems

Secondary glazing has been used in heritage and listed properties for decades, but not all systems are built the same way. When you start comparing options, three things tend to separate a genuinely good system from an average one: how well it works with existing shutters, what it’s actually made from, and how precisely it’s fitted to each individual window. This is where the CSG System does things differently.

The Shutter Problem Most Systems Ignore

Anyone with working internal shutters knows the frustration: many secondary glazing systems simply weren’t designed with shutters in mind. Standard off-the-shelf units are often too bulky to sit in the reveal alongside a shutter box, forcing homeowners to choose between keeping their shutters functional or improving their windows’ performance — sometimes even packing shutters shut permanently just to fit a secondary glazing frame.

The CSG System was built around the opposite priority. It’s designed from the outset to sit within the same space as existing shutters, so they continue opening, closing and folding exactly as they always have. For a period home, that matters — shutters aren’t just decorative, they’re often original, and in many cases they’re doing real thermal and security work of their own.

Glass vs Plastic: What You’re Actually Installing

Not all secondary glazing is glazing in the true sense. Several systems on the market use acrylic or polycarbonate panels instead of glass, which can be lighter and cheaper but tend to scratch more easily, discolour over time, and don’t always match the clarity or feel of a traditional window.

CSG uses toughened safety glass as standard — 4mm as the base option, with a 6.8mm acoustic-rated glass available for homeowners prioritising noise reduction. That’s a meaningful difference for a heritage property specifically, where sightlines and the authentic look of glass (rather than a plastic sheen) matter for keeping the character of the room intact.

Built for Listed Buildings, Not Retrofitted to Them

A lot of secondary glazing is designed as a general-purpose product, then adapted afterwards for period or listed properties. CSG was developed the other way round — specifically for sash and case windows in conservation areas and listed buildings from day one.

That distinction shows up in the details: because secondary glazing doesn’t alter or remove any part of the original window, it’s classed as reversible, which is generally looked upon favourably by conservation officers compared to full window replacement. In every council area CSG has applied for listed building consent, approval has been granted without issue — a track record that only comes from designing specifically for this type of property rather than treating it as an edge case.

The Numbers Behind the Claims

Independent testing (via BRE) found the CSG System improves a window’s thermal efficiency by almost 50%, and it can reduce external noise by up to 50% as well. Those aren’t small margins — for context, well-fitted secondary glazing in general has been shown in academic and conservation studies to rival or even outperform full double glazing in some cases, without any of the disruption or loss of historic fabric that comes with replacing the original window.

A Bespoke Fit, Including Curved Windows

Off-the-shelf secondary glazing struggles with anything non-standard, and period properties are rarely standard. Bay windows, arched heads and curved sash windows are common in Georgian and Victorian homes, and many systems simply can’t accommodate them.

CSG is made to measure for each window, including curved sash windows — so instead of a compromise fit that leaves gaps (and therefore leaks heat and noise straight back in), each unit is built for the exact opening it’s going into.

The Bottom Line

Secondary glazing only works as well as its weakest compromise — whether that’s a shutter it can’t work around, a material that doesn’t hold up, or a fit that doesn’t quite match the window. The CSG System was designed to remove those compromises for heritage homes specifically: full shutter compatibility, real glass, a proven track record with listed building consent, and a bespoke fit for every window shape, sash and case included.

Interested in seeing how the CSG System would work on your property? Get in touch for a free quote or to book a showroom visit.