Secondary Glazing Installation and Replacement Cost Calculator

How this calculator works

This calculator estimates a realistic price range rather than a single figure, because real-world quotes genuinely vary that much. It starts from typical UK supplied-and-fitted price ranges drawn from published 2026 industry cost guides, then multiplies them by the number of units you enter and by adjustment factors for each choice you make below. The result is a low-to-high band that a fair quote is likely to fall within, not a promise of the exact price you will pay.

Secondary glazing typically costs around to per window supplied and fitted in 2026, with a whole-house installation on a three bedroom property commonly landing around to . Because the original windows remain in place, secondary glazing usually needs no planning permission even on listed buildings, and with a deep air gap it can outperform replacement double glazing for noise reduction, reaching 45 decibels or more.

Number of windows to treat

Enter how many windows you want to fit with secondary glazing. Because each unit is independent, it is easy to phase the work room by room, starting with bedrooms facing the noise or the coldest rooms.

Window size

Size is one of the biggest cost drivers for any glazed unit. A larger opening needs more frame material and a bigger, heavier sealed glass unit, and it usually takes longer to fit. The calculator uses three broad size bands based on common UK window dimensions: choosing the small band reduces the typical range by around 20 percent, while the large band increases it by around 40 percent. If your windows vary in size, run the calculator once per size band and add the results together.

Panel style

Fixed panels are the cheapest option, at published prices of roughly to per window, and suit windows you never open. Horizontal sliders are the most popular all-rounder. Vertical sliders mirror the operation of sash windows behind them and cost a little more. Hinged and lift-out panels give full access to the original window for cleaning and ventilation.

Glass type

Standard 4 mm glass is included in baseline prices. Acoustic laminated glass, typically 6.4 mm or thicker, adds roughly to per window and significantly improves noise reduction, which is the main reason many people fit secondary glazing. Low-E coated glass adds roughly to and improves thermal performance, useful where heat retention rather than noise is the priority.

Specification level

Two windows that look similar from the street can sit at very different price points. Budget products use simpler profiles, standard hardware and basic glass. Mid-range covers the typical A-rated units most UK installers quote by default. Premium covers high-end systems with upgraded security hardware, better thermal performance, special finishes or designer profiles, and typically adds around 30 percent to the price.

Where you live

Labour rates are not uniform across the UK. Published cost guides consistently show installation prices in London and the South East running roughly 20 to 30 percent above the national average, driven by higher labour costs, travel, parking and congestion charges. The calculator applies an uplift of around 20 percent if you select London and the South East. Product prices themselves are broadly similar nationwide, so the difference mostly reflects fitting costs.

What else affects the price

Secondary glazing prices scale with the size of each opening, the panel style and the glass specification. Reveals that are out of square, which is common in period properties, need timber grounds or scribing that adds fitting time. Performance depends heavily on the air gap, with 100 to 200 millimetres between the original glass and the new panel giving the best acoustic results, and on tight perimeter sealing. DIY kits can save 30 to 40 percent on the installed price, but professional systems fit better, look slimmer and carry warranties, which matters in heritage settings.

Planning permission, building regulations and certification

Like-for-like window replacement on most houses does not need planning permission, but listed buildings always require consent and conservation areas often restrict materials and styles on visible elevations, so check with your local planning authority if either applies. Building regulations apply to every replacement window in a dwelling, setting minimum energy performance and safety glazing standards. Installers registered with a competent person scheme, such as FENSA or Certass, can self-certify compliance and issue a certificate after completion; otherwise you must arrange building control sign-off separately. Keep the certificate safe, as buyers’ solicitors routinely ask for it when you sell.