Secondary Glazing for London's
Listed & Period Properties
Acoustic and thermal secondary glazing that silences traffic noise and ends draughts — without altering a single original window. Engineered for Grade I & II listed properties and conservation areas. We beat any like-for-like quote.
Contact us for information, quotations & free appointments
Manufacturers & Specialist Installers of Secondary Glazing
We're manufacturers and specialist installers of secondary glazing with over 30 years of industry know-how and knowledge. Every unit is made in-house and continuously refined against the highest performance standards, and we boast the lowest profiles on the market. No subcontractors, no compromises, just skilled tradespeople who take genuine pride in their work.
- 30+ years of industry know-how & knowledge
- The lowest profiles on the market
- In-house manufacturing & installation
- Grade I & II listed specialists
- Acoustic & thermal glass, refined to peak performance
- Free site survey across London & the UK
Could not believe the difference
We're on a busy road in Kensington — even with the windows shut you could hear every bus. After Glasswise fitted secondary glazing the bedroom went from constant rumble to total silence. Genuinely life-changing.
Perfect for our Grade II listed flat
Conservation officer signed off straight away. The secondary panels are practically invisible behind our original sashes. House is finally warm in winter and we can sleep through the morning bin lorries.
Heating bill cut by a third
Our Victorian terrace was draughty everywhere. Glasswise surveyed and installed in two visits — no mess, no damage to the original windows. First winter we noticed the rooms were warm and the heating ran for half as long.
Best decision we made on the house
We sit right under the Heathrow flightpath in Richmond. The Stadip acoustic glass spec cut the plane noise to a faint hum. Honest, professional team — no pressure selling, no hidden costs.
Slim profile — barely visible
I was worried secondary glazing would ruin the look of our Georgian sashes. Honestly you have to be in front of the window to see it's there. Colour matched perfectly to the existing frames.
Specified for our riverside development
As an architect I've worked with Glasswise on three listed-building schemes now. Their attention to profile detail and willingness to colour-match makes them an easy first recommendation.
What is Secondary Glazing?
Secondary glazing is a fully independent window system installed discreetly on the inside of your existing windows — leaving the original window completely untouched.
A second pane of high-performance glass is set within its own slim frame, creating a sealed insulating air gap between the original glazing and the new pane. It is this air gap, combined with the mass of the additional glass, that delivers a dramatic reduction in noise transmission, heat loss and draughts.
Because nothing about the external appearance changes, it is the preferred upgrade for period, listed and conservation-area properties where replacement windows are not an option.
One system. Three problems solved.
Why choose Glasswise for secondary glazing in London
Premium Aluminium
Architectural-grade extrusions in our slim 37mm profile — strong, slim, built to last.
UK Manufactured
Built to order at our UK workshop. Engineered, finished and quality-checked under one roof.
Low Maintenance
Sealed aluminium frames that won't warp, rot or need repainting — wipe-clean by design.
Unbeatable Lead Times
Surveyed, manufactured and installed within 2–3 weeks for most projects.
Bespoke to the Millimetre
Every unit is measured, manufactured and finished specifically for one opening — no standard sizes, no compromises.
Free Home Survey
No-obligation home visit by one of our specialists before any quotation.
Heritage protected.
Performance retrofitted.
Secondary glazing is the only retrofit solution officially endorsed for listed buildings and conservation areas. Because the original windows remain untouched, planning consent is rarely required — even on Grade I properties.
- Reversible installation — original windows untouched
- No planning permission required in most cases
- Approved by conservation officers across all 32 London boroughs
- Slim 37mm aluminium profile — virtually invisible from outside
Project Gallery
Recent installations across London's listed properties, period homes and commercial developments — every project surveyed, manufactured and installed by our in-house team.
LondonSliding secondary glazing
Sliding systemHorizontal slider
On-siteInstallation in progress
Acoustic specPeriod property
Period townhouseTall sash windows
Heritage styleWindow upgrade
KensingtonSash window retrofit
West EndCommercial installation
RAL-matchedCustom colour finish
HeritageOriginal sashes preserved
Grade II ListedHeritage property
Conservation areaDiscreet installation
Slim profileInvisible from outside
BespokeCustom secondary glazing
LondonVictorian bay window
KensingtonResidential retrofit
Period propertyAcoustic installation
MayfairSlim aluminium system
LondonSecondary glazing project
Our Window Styles
Four independent secondary glazing systems, each engineered to mirror an original window configuration without altering it. Use them individually, or combine them across a single property — every aluminium frame is precision powder-coated to any of the 150+ standard RAL colours for a finish that disappears against your existing décor.
Vertical sliding
Secondary glazing sash windows
Counter-balanced vertical sash operating on tensioned springs — panels stay open at any height. Ultra-slim 37mm aluminium frames make this our most discreet system for traditional sash windows.
Ideal for Victorian and Georgian townhouses where preserving the original sash aesthetic is critical. Operates silently and discreetly behind original sashes.
| Style Reference | 01 / Sash |
|---|---|
| Operation | Counter-balanced vertical sash |
| Frame Profile | 37mm × 37mm aluminium |
| Transom Coupling | 15mm slim line |
| Glass Range | 4mm – 6.8mm |
| Glass Options | Acoustic / Thermal |
| Colour Options | 150+ RAL · custom matched |
| Listed Compliant | Grade I & II |
Options / Features
Horizontal Sliding
The most versatile system in our range — ideal for Crittall, traditional casement, and long stretches of commercial glazing. Configured to mirror any layout with 2 to 8 panels.
Perfect for commercial premises, offices, retail and any space where wide window runs need treating economically. Steel rollers provide silent, lifetime operation.
| Style Reference | 02 / Slider |
|---|---|
| Operation | Horizontal sliding panels |
| Panel Options | 2 · 3 · 4 · 6 · 8 panel layouts |
| Track System | Single or triple track |
| Bearing System | Low-maintenance steel rollers |
| Removable Panels | Yes — full access to original |
| Best For | Crittall · Casement · Commercial |
| Colour Options | 150+ RAL · custom matched |
Options / Features
Lift-Out Panel
The slimmest and most discreet system in our range — panels lift out completely for cleaning or full access to the original window. Ideal for fixed lights and bespoke configurations.
A favourite for awkward window shapes and heritage projects where the secondary glazing must be virtually invisible. Frequently combined with sash or sliding systems for bespoke window layouts.
| Style Reference | 03 / Removable |
|---|---|
| Operation | Lift-out (fully removable) |
| Frame Profile | Discreet low-profile aluminium |
| Glass Options | Acoustic / Thermal |
| Accessibility | Full panel removal |
| Coupling | Combines with other systems |
| Best For | Fixed lights · bespoke shapes |
| Colour Options | 150+ RAL · custom matched |
Options / Features
Hinged Casement
A traditional hinged system that mirrors original casement windows or doors. Available in single or French double configurations — ideal for casements and balcony doors.
A natural choice where the original window opens inward or where balcony access is required. Heavy-duty hinges support thick acoustic glass without sagging over decades of use.
| Style Reference | 04 / Casement |
|---|---|
| Operation | Hinged (single or double) |
| Configurations | Single & French double |
| Hinge System | Heavy-duty engineered |
| Locking | Internal locking mechanism |
| Glass Options | Acoustic / Thermal |
| Best For | Casements · balcony doors |
| Colour Options | 150+ RAL · custom matched |
Options / Features
Sound Proofing Windows
with secondary glazing
Cut up to 80% of the noise coming through your windows with our ultra-low-profile aluminium secondary glazing — all the quiet, none of the bulk.
The science behind the silence
Achieving up to 80% sound reduction depends on two elements working together: Saint-Gobain's 6.4mm Stadip Silence acoustic laminated glass, installed behind an air gap of at least 120mm. Each plays a distinct role — neither delivers the full result on its own. The glass absorbs and dampens sound vibrations, while the wide air gap disrupts the remaining sound waves before they reach the room.
SGG Stadip Silence™
6.4mm acoustic laminated · 3-Ply PVB · 54dB max attenuation · Safety & security rated
Two panes of glass bonded with a 3-ply acoustic PVB interlayer whose soft, noise-dampening core absorbs sound vibrations far beyond standard laminated glass — while the laminated build also adds safety and security, making it ideal for ground-floor windows and balcony doors.
Recommended Air Gap
- Sound Reflection and Absorption: The air gap acts as a buffer between the two glass layers. Sound waves penetrating the first pane are partially reflected back and partially absorbed within the cavity before reaching the second pane, dramatically reducing the energy that makes it inside.
- Higher STC Rating: The combined effect of glass mass, the depth of the air gap, and the resonance created by the recommended 120mm+ cavity delivers a significantly higher Sound Transmission Class rating — measurably less noise transferred from outside to inside.
- Reduction of Vibrational Path: The air gap minimises direct vibration transmission between the exterior and interior pane by acoustically decoupling them, so sound can't travel through a shared rigid path — further cutting noise transmission.
The dotted area represents the 125mm recommended air gap for optimal sound reduction results.
The blue frame represents the position of the secondary glazing system with the recommended 125mm air gap.
Expected sound reductions with secondary glazing
Measured Rw dB reduction using Saint-Gobain Stadip Silence™ 6.4mm acoustic laminated glass across the four standard secondary-glazing cavity depths. The wider the cavity, the deeper the silence.
SGG Stadip Silence™
Heavy traffic noise dropped to the level of a quiet library — an immediate, audible step-change indoors. Entry-level acoustic spec.
Busy urban traffic reduced to whisper level — calm, conversational interior with no raised voices. Strong improvement, good for back rooms.
The point where the cavity starts delivering its full acoustic potential. Traffic, voices and general urban hum reduced to a soft background presence. Our minimum recommended spec.
Main-road noise reduced to barely audible — restful sleep and undisturbed focused work, even with windows facing busy streets. Heritage-grade acoustic spec.
Heaviest traffic, sirens, trains and flight paths brought to near-silence — recording-studio quiet. Maximum acoustic performance.
Rw values represent the weighted sound reduction index measured to BS EN ISO 717-1. A 10dB drop is perceived as roughly halving the loudness — so a 40+dB reduction makes external traffic feel essentially absent. Figures are representative; exact performance depends on existing window condition, building fabric and installation specifics.
Reduce up to 80% of noise with our architectural low profile secondary glazingrequest a free site survey or an instant online quotation.
Thermal Insulation
with secondary glazing
Eliminate heat loss and draughts through your windows with our low-profile, airtight independent secondary glazing window system.
A complete thermal barrier — sealed, insulated, draught-proof
Up to 40% of a room's heat escapes through traditional single-pane windows. Our independent secondary glazing system pairs Pilkington Low-E glass with a fully gasket-sealed aluminium frame fitted in front of the existing window — completely eliminating air escaping or infiltrating through deteriorated putty, shrunken timber and pulley cavities. The Low-E coating reflects radiant heat back into the room while the sealed cavity blocks conductive heat loss, condensation and noise — all without altering a single original window.
Pilkington Low-E K Glass™
6mm Low-E coated · Heat-reflective coating · Up to 70% less radiant heat loss · Daylight retained
A microscopically thin, transparent metallic oxide coating bonded to the inner pane reflects radiant heat back into the room while letting natural daylight pass through — slashing heat loss in winter and keeping interiors cooler in summer.
Airtight Independent Window System
- Fully airtight system: Our secondary glazing panel forms a complete, gasket-sealed barrier around the window opening — eliminating air leaks through deteriorated putty, shrunken timber and pulley cavities, so heat can't escape and cold air can't infiltrate.
- Heat retention: The sealed buffer between the existing window and the secondary panel traps a layer of still air, acting as a thermal barrier that dramatically slows conductive heat loss from inside to outside.
- Condensation control: The sealed barrier raises the inner surface temperature of the glass, dramatically reducing condensation and preventing the internal mould and timber rot that typically follow.
Secondary glazing — answered
Honest, direct answers to the questions our heritage clients ask most.
Do I need planning permission for secondary glazing in a listed building?
In most cases, no. Because secondary glazing is installed internally and leaves the original window untouched, it is generally considered a reversible alteration and falls outside the scope of listed-building consent.
Historic England explicitly endorses secondary glazing as an appropriate measure for improving thermal and acoustic performance in historic buildings. We can liaise directly with your conservation officer if any sign-off is required.
How much noise reduction can I realistically expect?
With our acoustic spec (Saint-Gobain Stadip Silence™ 6.4mm laminated glass and a 125mm air gap) we typically deliver 40–60dB reduction in measured external traffic noise. On a recent Belgravia install we measured 78dB on the street and 18dB inside the room — close to total silence.
Performance varies with original window condition and air gap, which is why we survey before quoting.
Will it look obtrusive behind my original sash windows?
Our aluminium profile is 37mm × 37mm — among the slimmest available in the UK — and the transom couplings between glass panels are just 15mm. Powder-coated to match your existing frame colour, the secondary glazing is virtually invisible from outside and barely perceptible from inside.
How long does the whole process take?
From your initial enquiry to final fit, expect 4–6 weeks: typically 1 week to survey, 48 hours to quote, 3–4 weeks for bespoke manufacture, and 1–4 days on-site to install — depending on the number of windows.
How much should I budget for my whole house?
Typical full-home secondary-glazing projects (8–14 windows) range from £4,000 to £12,000 depending on glass specification, frame colour and any bespoke profile requirements (bay, arched, lift-out etc.). See our pricing guide above for per-window indicative rates.
Can I still open my original windows after installation?
Yes. Every Glasswise system is designed to operate independently of the original window. Sash, sliding, hinged and lift-out configurations all allow full access to the original window for cleaning, maintenance or ventilation.
What guarantee do you provide?
Standard installations come with a 10-year guarantee on workmanship and materials. Acoustic and Heritage specifications carry an extended 12-year guarantee. All glass is supplied by Saint-Gobain or Pilkington under their own manufacturer warranty.
From first call to final fit in 2–3 weeks
Free Site Survey
One of our specialists visits your property to measure each window, discuss acoustic or thermal priorities, and assess any conservation requirements.
Within 7 daysDetailed Written Quote
A precise, itemised quotation with frame profile, glass specification, RAL colour match and lead-time. No hidden costs. Conservation-officer-ready.
48-hour turnaroundBespoke Manufacture
Every frame is fabricated to the millimetre at our UK workshop. Aluminium powder-coated to your chosen RAL, glass laminated to spec.
1–2 weeksClean Installation
Our installers protect every surface, fit each unit, and leave the property as they found it. Typically completed in 1–4 days depending on window count.
1–4 days on-site