Secondary Glazing Costs UK — What to Charge to Install It in 2026

What Secondary Glazing Is — and How It Differs

Secondary glazing is a discreet, fully independent pane fitted to the inside of the existing window, set back from the original glass by an air gap of typically 100–200mm. The original window stays exactly where it is. That single fact is what makes the product so useful — and it's the line that closes most jobs in period and listed properties.

It is not double glazing, and it is not a replacement window. Double glazing seals two panes into a single sealed unit and replaces the whole window. Secondary glazing adds a second, separate window in front of the existing one, leaving the original intact and fully reversible. Because nothing original is removed or altered, it is the go-to solution for listed buildings, conservation areas and anywhere the existing windows must be preserved.

Why Clients Choose It Over Replacement

• Listed buildings: Reversible secondary glazing usually does not require listed building consent, whereas replacing the windows almost always does — and is frequently refused.
• Conservation areas: The external appearance of the property is unchanged, so there is no impact on the streetscape that a planning officer would object to.
• Noise: The wide air gap and heavier glass options deliver noise reduction that sealed double-glazed units struggle to match for low-frequency traffic and rail noise.
• Cost: Per opening, secondary glazing is usually cheaper than a like-for-like timber sash replacement, especially on bespoke heritage joinery.

Types of Secondary Glazing and What to Charge

The opening style you fit affects both your material cost and the price you can reasonably charge. The right type depends on the original window — a vertical sliding sash usually pairs with a vertical slider so both panes operate together — and on how the client needs to use the room.

Hinged / Casement Units

A side-hung or top-hung pane that opens inward on hinges. Simple, well-sealed and cost-effective for smaller windows and where occasional full access to the original window is needed for cleaning or ventilation. The most common entry-level product.

• Small standard window: £300–£500
• Medium window: £450–£750

Vertical and Horizontal Sliders

Sliders are the most popular choice for period homes. A vertical slider mirrors the action of a sash window and lets the client open both panes for ventilation; a horizontal slider suits wider windows and modern openings. They carry a higher material and fitting cost than a simple hinged unit because of the tracks, balances and tighter tolerances involved.

• Medium sliding unit: £600–£1,000
• Large sliding unit: £900–£1,500

Lift-Out and Fixed Units

Lift-out units are removable panes ideal for windows that are rarely opened but may need seasonal access — they sit in a frame and lift away entirely. Fixed units are sealed permanently in place and are the cheapest option per pane, suited to windows that never need to open, such as fixed lights, landings or feature panes. Both keep costs down where opening function isn't required.

• Fixed unit (small to medium): £300–£600
• Lift-out unit: £350–£650

Frame Finishes

Most secondary glazing is fitted in slimline aluminium, which is strong, narrow and powder-coated to a wide range of RAL colours. White is standard, but heritage clients frequently specify a colour to match existing joinery, or a timber-effect or woodgrain foil finish — both add to the price. Brown, bronze and bespoke RAL colours typically add 10–15% to a unit. Always confirm the finish in writing before ordering, as colour-matched frames are non-returnable.

What Drives the Price

Two windows of the same size can carry very different prices depending on the spec. Before you commit a figure, work through these cost drivers:

• Window size: The single biggest driver. Larger openings need heavier sections, more glass and often two people to fit safely.
• Opening type: Fixed and hinged units are cheapest; sliders and lift-outs cost more in materials and labour.
• Glass specification: Acoustic laminated glass for noise reduction is dearer than standard float, and low-E glass for heat retention adds cost again. The thicker the acoustic glass, the higher the dB improvement — and the higher the price.
• Number of units: Whole-house jobs carry better margins per window because survey, travel and setup are spread across multiple openings.
• Access: Upper floors, bay windows, deep reveals and awkward heritage openings all add survey and fitting time.
• Bespoke vs standard: Out-of-square period reveals, arched heads and oversized sashes need bespoke fabrication, which carries a clear premium over off-the-shelf sizes.

Glass Spec: Acoustic vs Low-E

The glass you specify should follow the client's reason for buying. For noise — the most common driver — fit acoustic laminated glass, typically 6.4mm to 10.8mm. Combined with the wide air gap of secondary glazing, this can deliver a noise reduction of around 45–54 dB, a substantial improvement over a single-glazed sash at roughly 25–30 dB. Because the human ear perceives a 10 dB reduction as roughly halving the loudness, that difference is dramatic for a client living on a main road or near a railway line.

For thermal performance and draught control, low-E (low-emissivity) glass reflects heat back into the room and the trapped air gap acts as an insulating buffer. Many clients want both, so a laminated acoustic pane with a low-E coating is a common upsell. Set the client's expectations clearly: secondary glazing significantly cuts noise and draughts but will never fully match a modern sealed double-glazed unit on raw U-value — its strengths are noise, draught reduction and heritage compatibility.

Listed Buildings and Planning

This is the part of the job that wins the work, so get it right. Because reversible secondary glazing does not alter or remove the original window, listed building consent is usually not required — it is widely regarded as a reversible internal alteration. This is the central selling point for owners of listed homes who have been told they cannot replace their windows.

However, "usually not" is not the same as "never". Advise the client to confirm with their local conservation officer before work begins, particularly for Grade I and Grade II* properties, where even internal alterations can be scrutinised. In conservation areas, secondary glazing is rarely an issue because the external appearance of the building is unchanged. Putting this advice in writing on your quote protects you and reassures the client that you understand the heritage context — which sets you apart from a fitter who just sends a number.

The Benefits Clients Pay For

Understanding what motivates the enquiry helps you tailor your quote and close the job. The main drivers are:

• Noise reduction: The strongest driver in cities and near transport links. A measurable dB improvement is something clients will pay a premium for, especially in bedrooms.
• Draught and heat reduction: Period single-glazed windows are draughty and cold. The air gap and seals cut draughts and lower heating bills without touching the original window.
• No planning headaches: For listed buildings, the absence of a consent application is itself a major benefit — clients avoid months of delay and the risk of refusal.
• Condensation control: Reducing draughts and cold surfaces helps cut condensation on the original glass, protecting historic joinery.

Trades and Labour

Secondary glazing is largely a fitting trade. A competent joiner or window fitter can survey, order and install, but the survey is where the money is made or lost — period reveals are rarely square, and a millimetre error on a bespoke slider means a non-returnable frame that doesn't fit. Budget proper survey time and measure every opening individually rather than assuming a row of windows is identical.

A two-person team can usually fit between four and eight standard units in a day once on site, depending on access and whether the openings are bespoke. Upper floors, bays and deep reveals slow this down. Always include survey time, travel and any making-good of the reveal in your labour calculation — clients notice a tidy finish, and it's what generates referrals in heritage neighbourhoods.

Typical Price Tiers per Window

As a rule of thumb for pricing a single opening supplied and fitted in 2026:

• £300–£600 — a small standard unit (hinged or fixed, standard glass).
• £600–£1,200 — a medium acoustic or sliding unit (laminated glass, vertical or horizontal slider).
• £1,200–£2,500+ — a large bespoke or feature window (oversized, arched, heavy acoustic glass, out-of-square reveal).

Price toward the top of each range in London and the South East, on heritage and listed properties, and where access is difficult. Whole-house jobs let you sharpen the per-window figure slightly while still protecting your margin.

Whole-House Example

A typical three-bedroom Victorian terrace with around 8–10 windows fitted with mid-range slimline aluminium secondary glazing — a mix of vertical sliders and a couple of fixed units, standard acoustic-lite glass — usually lands somewhere between £5,000 and £9,000 supplied and fitted. Move to full acoustic laminated glass throughout and bespoke sizing on bays, and the same property can reach £10,000–£14,000. Always quote per window as line items so the client can see exactly where the money goes and trim spec on lower-priority rooms if needed.

Worked Example: Flat With 6 Sash Windows

A first-floor period flat on a busy main road, six original timber sash windows, client wants to cut traffic noise in the bedrooms and living room. You spec vertical sliding secondary glazing with 6.8mm acoustic laminated glass to mirror the sash action and maximise noise reduction.

• 4 medium acoustic sliders @ £950 each: £3,800
• 2 larger living-room acoustic sliders @ £1,300 each: £2,600
• Survey, fitting and making-good (2 days, 2 fitters): included
• Heritage RAL colour match to existing joinery (+12%): £768

Total supplied and fitted: roughly £7,168, delivering an estimated 45–50 dB of acoustic reduction across the rooms that matter. Because the work is fully reversible and the original sashes are untouched, no listed building consent is needed — but you note on the quote that the client should confirm with the conservation officer, and you document the existing window condition in a short survey report attached to the quote. That report is what elevates your price above a competitor who just sends a number.

Quick Reference: Secondary Glazing Prices UK 2026