Secondary glazing across the UK

Secondary glazing - what to expect

Secondary glazing is a separate internal window fitted inside your existing primary window, and it's the compliant answer to a set of problems that regular replacement can't solve: listed buildings, Grade II* fronts, conservation areas with strict Article 4 controls, and mid-terraces on busy main roads where noise is the bigger issue than thermal loss. Because it doesn't touch the primary window, it doesn't need Listed Building Consent in the vast majority of cases - a genuine 'yes' where the answer would otherwise be a slow, expensive planning nightmare.

Prices depend on the frame material (aluminium is standard, timber is available for internal aesthetic match on period rooms), the opening style (fixed, horizontal slider, lift-out, vertical sash to match a Georgian primary), and the glass. A typical aluminium horizontal slider on a 1.2m x 1.2m opening is £350-£550 fitted; upgrade to 6.8mm acoustic laminated glass (the meaningful noise-reduction spec) and you're at £550-£800; a bespoke timber vertical sash pair to match a Georgian window inside a Grade II listed drawing room can run £950-£1,600.

Two performance numbers matter. For thermal: a well-fitted secondary system delivers a whole-window U-value around 1.6-1.9 W/m²K when installed inside a single-glazed sash, versus 4.8 for the original alone - not as good as a modern A-rated unit, but a step change nonetheless. For acoustic: secondary glazing outperforms most double glazing on traffic noise because the wide (usually 100-200mm) air gap and different pane thicknesses break up the resonance frequencies that thin sealed units don't. Achieving 40-45 dB reduction is realistic with 6.8mm laminated glass and a 150mm+ cavity - the difference between an unusable front bedroom on a busy A-road and a genuinely quiet one.

Typical UK price range for secondary glazing: £350 - £950 installed. Actual figures for your city sit on the city page below.