Secondary glazing is a second, independent window fitted to the room side of the one you already have. The original frame and glass stay. That is why it costs less than replacement, why it is the standard answer on listed buildings, and why it is quieter than a double glazed unit: the gap between the two panes is 100 mm or more rather than 16 mm. It is also why the price depends far more on the type of unit than on the glass. This page gives the 2026 figures by type, by house, and for the kits you fit yourself, then sets them against replacement double glazing so you can see which your windows actually call for.
Secondary glazing cost per window in 2026
Three independent UK cost guides published in 2026 land close together. Checkatrade prices a standard window at £300 to £500 fitted. The Federation of Master Builders puts the average at around £400 with a ceiling of about £700. MyJobQuote's average is £275 to £400. The spread inside those figures is the type of unit: a panel you lift out to clean the original window is the cheapest, a hinged casement or a vertical slider engineered to sit behind a sash window is the dearest, and the large bespoke aluminium systems used on heritage buildings run to £900.
| Type of secondary glazing | Fitted, per window | Best for |
|---|---|---|
| Magnetic panel (acrylic or polycarbonate) | £205 to £360 | Budget, rented homes, DIY |
| Lift-out fixed panel | around £310 | Windows you rarely open |
| Horizontal slider | £415 to £515 | Casement windows, wide openings |
| Vertical slider | £415 to £515 | Sash windows; slides to match the original |
| Hinged casement unit | £465 to £570 | Windows you open often; full access for cleaning |
| Bespoke heritage aluminium system | up to £900 | Listed buildings, large or shaped openings |
Source: Federation of Master Builders (January 2026) per-type averages; Checkatrade (July 2026) £300 to £500 for a standard window; MyJobQuote (March 2026) £275 to £400 average. Bespoke ceiling from specialist installers.
Two things sit outside the table. Low-emissivity glass in the secondary pane, which is what produces the Historic England heat-loss figure below, adds to the glass cost but not the labour. And the frame material: uPVC secondary systems are the most economical, while slim aluminium is what the specialist installers use on period buildings because it sits almost invisibly inside the reveal.
What a whole house costs
Secondary glazing is priced per opening, so the house figures track the window count. The 2026 trade figures below split materials from labour, and the split is the point: labour is a small share, because nothing is removed. Two fitters at £130 to £200 a day each finish a typical house in one to two days, at one to two hours per window, and sash windows or awkward shapes take longer.
| Property | Windows | Materials | Labour | Total fitted |
|---|---|---|---|---|
| Flat | 4 | £1,100 to £1,650 | £250 to £300 | £1,350 to £1,950 |
| Small terrace | up to 8 | £2,350 to £2,850 | £400 to £475 | £2,750 to £3,325 |
| Semi-detached | up to 10 | £3,000 to £3,500 | £700 to £775 | £3,700 to £4,200 |
| Detached | up to 15 | £4,600 to £5,250 | £875 to £1,100 | £5,475 to £6,150 |
Source: MyJobQuote, March 2026. Compare with our double glazing cost by house size, where a ten-window semi in fitted uPVC casements is £5,000 to £12,000.
DIY secondary glazing: what the kits cost
The magnetic systems are made for fitting yourself. A steel tape goes on the frame, a magnetic strip on a sheet of acrylic or polycarbonate cut to size, and the panel lifts off for cleaning or summer. Priced from the current UK suppliers, 3 mm polycarbonate is about £46 per square metre (2 mm £33, 4 mm £59) and a 5 m magnetic tape kit around £21, so a 1.2 by 1.0 m window is roughly £75 to £80 in materials before VAT, and starter kits are sold from about £27 plus the sheet. The Energy Saving Trust ranks the options by thermal benefit: film the least, magnetic panels a genuine step up, permanent fitted systems the most, and notes that permanent secondary glazing "can be more energy efficient than replacing the windows".
The limit of DIY is the sliding and hinged units. They are made to measure in aluminium, and the supplier fits them, which is where the £400 to £700 figures come from. There is also, as the Energy Saving Trust points out, no central body that certifies secondary glazing installers the way FENSA certifies replacement windows, so the supplier's own guarantee is the thing to read.
What you get for the money: heat
The best UK evidence is Historic England's own test programme on timber sash windows. A typical single glazed timber window loses heat at around 4.8 W/m²K. Adding a plain secondary pane takes that to roughly 2.5, and a low-emissivity secondary pane to below 2.0, against 1.0 to 1.4 for A-rated double glazing. Their measured test window went from 4.3 to 1.8 W/m²K whole-window with low-E secondary glazing, a 58% reduction, and 63% through the glass alone; Historic England's published guidance rounds that to "over 60%". The same tests found the air leakage through the window fell from 183 cubic metres an hour to 8 with secondary glazing in place, which is the draught stopping most people notice first. Our guide to U-values explains the scale.
Two design points from the same research. The optimum air gap for heat is 16 to 20 mm; wider than that and convection starts moving heat across the cavity. That conflicts directly with what noise wants, below, so the cavity is a choice. And a secondary system that seals well matters more than the glass: the thermal benefit comes as much from decoupling the draughty original frame as from the second pane.
Where secondary glazing beats double glazing: noise
A sealed double glazed unit holds its two panes 16 mm apart and rigidly connected, so they resonate together and the unit performs, in the specialist installers' own words, "little better than a single pane" for sound: about 34 dB for a standard 4-16-6 unit. Secondary glazing puts 100 mm or more between the panes, which decouples them. Historic England's guidance gives "up to 45dBA" at a 100 mm cavity; Selectaglaze's tested figures are 45 to 50 dB at 150 mm, and in excess of 50 dB when secondary glazing is fitted over double glazing. Every 10 dB is roughly a halving of perceived loudness. The catch is sealing: a gap of 1% of the window area can cost up to 10 dB, so a badly fitted system loses most of the advantage. If noise is the reason you are here, our guide to acoustic double glazing sets the sealed-unit options against this one.
Planning, listed buildings and VAT
Historic England's position is plain: installing reversible secondary glazing "does not generally need listed building consent", whereas putting double glazing into historic windows "will usually require" it and replacing the windows "will always require consent". That is why the cost comparison on a listed building is not secondary against replacement; it is secondary against an application, a conservation officer and, often, a refusal. Our listed building cost page and conservation area rules cover the consents in detail.
VAT is the trap. The zero rate on energy-saving materials, which runs to 31 March 2027, does not include glazing of any kind: HMRC's notice lists "secondary or double glazing, low-emissivity glass" as standard-rated, so every figure on this page carries 20%. Draught stripping fixed around windows is on the zero-rate list, which means a draught-proofing job on the same sashes can be invoiced at 0% while the secondary glazing next to it is at 20%. Worth asking a supplier to split the two.
Secondary glazing or replacement double glazing?
Per window, secondary glazing at £300 to £500 against a fitted uPVC casement at £400 to £1,000 looks like an easy saving. Across a house the gap narrows, because both are priced per opening: the Energy Saving Trust puts a set of A-rated windows for a semi at around £4,800, and the same semi in secondary glazing is £3,700 to £4,200. Secondary glazing lasts 20 years or more with no sealed cavity to fail, keeps original windows that may be part of the house's value, and wins outright on noise. Replacement wins on the thermal ceiling, on a window that is rotten or beyond repair, on cleaning and on opening; a second window is a second thing to open. The full comparison, with the verdict, is in secondary vs double glazing, and the uPVC window calculator prices the replacement route for your own house.
It depends Secondary glazing: the right buy on listed and conservation-area homes, on sound original windows worth keeping, and wherever noise is the problem. Replacement double glazing where the original windows are failing and nothing stops you replacing them.
The homes where secondary glazing gets specified are the ones where the windows cannot be replaced. That is a pity, because on a noisy road it would often be the better answer even where replacement is allowed, and it is the only glazing upgrade that can be taken out again.
Double Glazing Cost Calculator Team
If replacement is the route after all
Where the original windows are failing rather than merely single glazed, secondary glazing keeps the problem behind a second pane. If you decide replacement is the answer, tell us what you have and Leads 2 Trade will arrange quotes for double glazing from installers covering your postcode. Say if the property is listed or in a conservation area; it changes what they can offer.
Frequently asked questions
£300 to £500 fitted for a standard window in 2026, with the trade average around £400 and the top of the range about £700 for hinged units and the vertical sliders that go behind sash windows. Lift-out panels sit at the bottom, around £310, and magnetic panels at £205 to £360. Large bespoke heritage systems can reach £900. Those are independent cost-guide figures; installers who specialise in listed work quote after a survey.
Roughly £1,350 to £1,950 for four windows, £2,750 to £3,325 for an eight-window terrace, £3,700 to £4,200 for a ten-window semi and £5,475 to £6,150 for a fifteen-window detached house, fitted, on 2026 trade figures. Labour is a small share of that: two fitters at £130 to £200 a day each finish most houses in one to two days.
Per window, yes: £300 to £500 against £400 to £1,000 for a fitted uPVC casement. Across a house the gap narrows, because secondary glazing is priced per opening at the same count. The Energy Saving Trust puts a set of A-rated windows for a semi at around £4,800; the same semi in secondary glazing is roughly £3,700 to £4,200. The better question is which one your windows allow, because on a listed building or in a strict conservation area, secondary glazing is often the only option that does not need consent.
For heat, nearly. Historic England's research on timber sash windows measured a reduction in heat loss of over 60% with low-emissivity secondary glazing, taking a single glazed window from around 4.8 W/m²K to below 2.0, against 1.0 to 1.4 for A-rated double glazing. For noise it is better: a secondary unit with a 100 mm cavity or more reaches 45 dB or beyond, where a standard sealed double glazed unit manages about 34 dB, because the wide gap stops the two panes resonating together.
Generally no. Historic England's position is that installing reversible secondary glazing does not usually need listed building consent, because it sits inside the reveal and leaves the original window untouched, whereas replacing the windows on a listed building always does. Check with your conservation officer if the installation would touch panelling, shutters or the frame itself.
No. The zero rate for energy-saving materials that runs to 31 March 2027 does not cover glazing of any kind; HMRC's VAT Notice 708/6 lists secondary and double glazing as standard-rated at 20%. Draught stripping fitted around the same windows is on the zero-rate list, so a draught-proofing job can be 0% while the secondary glazing beside it is 20%.
The magnetic and lift-out systems are designed for it. A 3 mm polycarbonate sheet cut to size is about £46 per square metre and a magnetic tape kit around £21, so a typical window is £75 to £80 in materials. Sliding and hinged aluminium systems are made to measure and fitted by the supplier; each window takes a fitter one to two hours.