Secondary GlazingThe Complete Guide
Secondary glazing is the most effective way to make single-glazed and period windows quieter and warmer — without replacing them. This guide explains what it is, how it works, what it costs, and how to choose the right system for your home.
What Is Secondary Glazing?
Secondary glazing is a slim, independent pane of glazing installed on the room side of your existing window. It does not replace your original glass — it works alongside it. The two panes trap a wide pocket of still air, and that air gap is what delivers the performance.
Because it is entirely internal, secondary glazing makes no change to the outside of your building. That single fact is why it is the preferred upgrade for listed buildings and homes in conservation areas, where replacing original windows is restricted.
The Key Benefits
- Dramatic noise reduction. The air gap absorbs sound energy, cutting traffic, aircraft and railway noise by up to 80%. With 10.8mm acoustic laminate glass you can achieve up to 54dB reduction.
- Warmer rooms, lower bills. Secondary glazing reduces heat loss through single-glazed windows by up to 65%, improving comfort and your U-values.
- No draughts or condensation. Sealed brush gaskets stop cold air and keep the inner pane warm, reducing condensation.
- Heritage-friendly and reversible. It preserves irreplaceable original windows while delivering modern performance.
Types of Secondary Glazing
The right style depends on how your existing window opens. The main options are:
- Vertical sliders — mirror traditional sash windows
- Horizontal sliders — ideal for wide openings
- Hinged casements — swing open for full access
- Lift-out units — removable, for seasonal use
- Fixed panels — slimmest and most affordable
For a side-by-side breakdown of every option, see our guide to the types of secondary glazing.
How Much Does It Cost?
Prices depend on window size, glass specification and how the unit opens. As a 2026 guide, standard units run £300–£800 per window, acoustic laminate £600–£1,200, and heritage grid-matched units £1,000–£2,200. For a full breakdown, read our 2026 secondary glazing price guide — and see whether it is worth it for your home.
Installation and Planning
Most installations are completed in 1–2 days with no external works. In the vast majority of cases no planning permission is required — read our guide to planning permission for secondary glazing. We serve period and listed homes across London, including Kensington, Westminster and Islington.
Secondary Glazing: Frequently Asked Questions
The most common questions about how secondary glazing works, what it costs, and where it can be fitted.
What Our Clients Say
Rated 4.9 out of 5 across 127 reviews from London homeowners.
"Exceptional service from start to finish. The noise reduction in our Kensington townhouse is remarkable — we no longer hear the constant traffic on the high street, even in the front bedrooms."
"Specialists who truly understand listed buildings. They handled our Grade II* property with real expertise and managed the conservation paperwork so we didn't have to worry about a thing."
"Our Georgian sash windows were draughty and freezing every winter. The secondary glazing has transformed the house — warmer rooms, lower heating bills, and the original windows look untouched."
"From survey to installation the team was professional and tidy. The fit is so discreet that visitors don't even notice the secondary glazing is there. Sleep has never been better."
"We live near a busy junction and the difference is night and day. The acoustic glass they recommended cut the noise dramatically. Worth every penny for the peace and quiet."
"Honest advice, fair pricing, and beautiful craftsmanship. They talked us through every option without any pressure. I would recommend them to anyone with a period property."
Get a Free Secondary Glazing Survey
Every home is different. The simplest way to get an accurate, no-obligation quote is a free survey, where we measure your windows and recommend the right specification.