FENSA Registered·Checkatrade 10/10 (279 reviews)·£5m Public Liability sales@swiftltd.co.uk·01322 221010 Swift Home ImprovementsAboutServicesAll services→ WindowsBi-fold DoorsComposite DoorsAluminiumWarm RoofsSkylightsuPVC DoorsConservatoriesRoof LanternsOrangeriesTimber WindowsSecondary GlazingFire Doors AreasAll areas→ LondonKentSurreyEssexGreenhitheDartfordBromleyBeckenhamChislehurstSevenoaks Our WorkReviewsContact01322 221010Request Free Quote - Home - Services - Secondary Glazing Secondary Glazing # Secondary glazing for periodand listed properties acrossKent, London and Surrey Keep the original windows, lose the draughts and most of the noise, with a discreet internal glazed system fitted for a fixed written price by the same family-run team since 1998. Request free quote 01322 221010 Listed-building friendly · £5m Public Liability · 10-year workmanship guarantee Since 1998 Family-run installer FENSA Registered installer 10/10 Checkatrade · 279 reviews 10 years Workmanship guarantee £10m Employers' Liability Overview ## What we do, secondary glazing 01 Secondary glazing is a slim independent glazed unit fitted to the inside of your existing window. The original window stays exactly as it is, and a second pane, usually in a slim aluminium frame that slides, lifts out or hinges open, is installed within the reveal. The air gap between the two does the work: it cuts noise substantially, stops draughts, and adds a layer of insulation without touching the outside of the building. 02 This service is for owners of listed buildings and properties in conservation areas where replacing the original windows is not permitted or not wanted, and for anyone on a busy road, under a flight path or near a railway line who mainly needs the noise to stop. We fit it in period houses, flats above shops, converted schools and chapels, and small commercial premises across Kent, London, Surrey and the South East. 03 Getting it fitted properly is what decides whether you notice it. The frames should follow the reveal and sit behind the original glazing bars so the window still reads as it should from inside and out. Seals must be continuous, because a single gap undoes much of the acoustic benefit, and the opening arrangement has to suit how you actually use the room, including access for cleaning and any escape-window requirement. All of that is a survey question, which is why we measure before quoting. Our work ## A snapshot of recent Swift installations Real photos from projects across Kent, London, Surrey and the South East. Tap through to see the full gallery. New white uPVC bay and casement windows with Georgian glazing bars fitted to a red-brick Kent home Close-up of a white uPVC sliding sash window with Georgian glazing bars and brass fitch fasteners in a red-brick wall Two-storey white uPVC bay windows with leaded glazing fitted to a mock-Tudor semi-detached home Close-up of a white uPVC bay window with slim top-opening vents in a painted render period bay White uPVC bay window and matching dormer window with Georgian glazing bars on a yellow-brick detached house Anthracite grey uPVC casement windows installed on a mock-Tudor brick and render family home Anthracite grey composite front door with side glazed panel under a newly clad gable porch roofline on a brick home White uPVC conservatory exterior with new tiled roof and lead flashing joining a red-brick house Bright conservatory interior with white uPVC casement windows, top-opening vents and a rooflight overlooking the garden White uPVC French patio doors and casement windows on a white rendered rear extension with a sandstone patio dining area, a Swift Home Improvements project White uPVC conservatory windows and French doors alongside new casement windows on a red-brick detached home with a tiled conservatory roof and lead flashing Modern white rendered home in Kent with black aluminium bi-fold doors and full-height Crittall-style windows at dusk See all recent work Why it matters ## What happens if you leave it Original single-glazed windows in a period property are usually the loudest and coldest part of the room. On a main road you hear every vehicle; in winter the cold radiating off the glass makes the room feel several degrees cooler than the thermostat suggests, and curtains move on a still night. For many of these houses the obvious fix is not available. Listed building consent for replacement windows is often refused, conservation areas restrict what can be installed, and leaseholders frequently cannot alter the external appearance of the building at all. Living with it means running heating harder every winter and losing sleep on the street side of the house, year after year. The mistake we see most often is cheap secondary glazing fitted badly: bulky white frames screwed across the reveal, no continuous seal, and panels too heavy to open, so the room becomes unusable in summer and the windows never get cleaned. Correctly specified secondary glazing should be barely noticeable and easy to operate. That is what we quote for. Our process ## From first call to sign-off - STEP 1 ### Sales representative visit One of our sales representatives visits to see the windows and the reveals, discuss what you most need to solve, noise, draughts or heat loss, talk through frame options and opening styles, and outline indicative pricing. - STEP 2 ### Surveyor & fixed written quote Our surveyor attends separately to measure each reveal precisely, check whether the reveal is square, note existing glazing bars, shutters, sills, radiators and any escape-window duty, then issue a fixed written quote. - STEP 3 ### Specification We agree the system, sliding, lift-out, hinged or fixed, the frame colour so it disappears against the existing joinery, the cavity depth for the performance you want, and the glass, standard, acoustic laminate or toughened where regulations require it. - STEP 4 ### Manufacture Units are made to your surveyed reveal dimensions. Lead times are usually shorter than full window replacement, and we confirm your fitting date as soon as the units land. - STEP 5 ### In-house fitting team install & sign-off Our employed fitters fix the frames to the reveal, seal continuously, adjust every opener, and leave the room clean. Nothing on the outside of the building is altered. Your 10-year Swift guarantee covers the workmanship and the units. Benefits ## What you actually get ### Substantial noise reduction A wide air gap between the original glass and the secondary pane is acoustically more effective than a sealed double-glazed unit, which is why it is used on main roads and flight paths. ### Original windows untouched Nothing is removed and nothing changes outside, which is what makes it viable on listed buildings, in conservation areas and on leasehold flats. ### Draughts eliminated The sealed inner frame stops the air movement that makes period rooms feel cold even when the heating is on. ### Warmer rooms, lower heat loss The trapped air layer reduces heat loss through the window opening, so the room holds temperature better and feels comfortable closer to the glass. ### Discreet when done properly Slim frames matched to the existing joinery colour, set behind the glazing bars, are hard to spot once you stop looking for them. ### Less disruption than replacement Installation is internal, quick and clean, with no scaffolding and no external works, which suits occupied flats and offices. Specification ## Secondary Glazing, how we specify Secondary glazing is simple in principle and detail-driven in practice. These are the choices that decide how well it works and how little you notice it. ### Opening styles Horizontal sliders suit wide casements and bays and are the most common choice. Vertical sliders pair naturally with sash windows and keep the visual logic of the window intact. Hinged casements suit narrow openings and give the fullest access. Lift-out panels are the least obtrusive and best where a window is rarely opened, and fixed panels are used where nothing needs to open at all. We match the style to how the room is actually used. ### Acoustic performance and the cavity Acoustic performance depends mainly on the width of the air gap and the mass of the glass. A wider cavity of around 100mm and above performs noticeably better than a narrow one, and acoustic laminate glass in the secondary pane adds further reduction. Where noise is the main reason for the work, we specify the widest cavity the reveal allows and seal it thoroughly. ### Thermal performance The still air layer between the two panes reduces heat loss and largely removes the cold downdraught you feel beside an old window. Low-emissivity glass in the secondary unit improves it further, which is worth considering on north-facing rooms and on large single-glazed openings. ### Listed buildings and conservation areas Because it is internal and reversible, secondary glazing is generally the most straightforward way to improve a listed or conservation-area window. Consent requirements still vary between authorities and can involve internal alterations to a listed interior, so we check the position rather than assume, and specify slim frames set within the reveal to minimise visual impact. ### Condensation, ventilation and escape windows Trapped moisture between the panes is the classic complaint after a poor installation. Getting it right means sealing the inner frame properly while leaving the original window ventilated to the outside, so moisture does not accumulate against the cold glass. Where a window serves as a means of escape, the secondary unit must open easily and fully. Both are survey questions we resolve before ordering. ### Where it is the wrong answer If your windows are rotten, structurally failing or already modern replacements, secondary glazing is a poor investment and we will say so. In those cases replacement windows or, in a period property, timber and timber-effect replacements are the better route, and we would rather quote you for the right work. FAQ ## Common questions ### How much noise does secondary glazing actually cut? +A well-sealed system with a wide cavity and acoustic glass typically makes a very noticeable difference on a busy road, generally more than replacing single glazing with a standard sealed double-glazed unit, because the wide air gap is what interrupts sound transfer. The result depends on the noise source, the cavity depth and how well the frame is sealed, so we assess it at survey. ### How much does secondary glazing cost? +Every property is different, so we do not publish rates. Price depends on the number and size of openings, the opening style, cavity depth, glass specification and access. Request a free survey and we will issue a fixed written quote before any work starts. ### Will it be visible from inside the room? +It is visible if you look for it, and largely unnoticeable if you do not. Slim frames finished to match the existing joinery, set within the reveal and behind the glazing bars, are far more discreet than the bulky white systems people remember from the 1980s. ### Do I need consent for a listed building? +Possibly. Secondary glazing is internal and reversible, which is why conservation officers often prefer it to replacement, but requirements differ between authorities and works to a listed interior can still need consent. We check the position for your specific property before anything is ordered. ### Can I still open my original windows? +Yes. Sliding, hinged and lift-out systems all allow you to reach and operate the original window behind, and we choose the style with that access in mind, including for cleaning. ### Will it cause condensation? +Not when installed correctly. The inner frame is sealed and the original window remains ventilated to the outside, so moisture is not trapped against the cold glass. Poorly sealed installations are the usual cause of the problem. ### Is it worth it if I already have double glazing? +Usually not for heat, occasionally for noise on very exposed sites. If you already have modern sealed units we will tell you honestly whether the improvement justifies the cost. ### How long does installation take? +Most homes are completed in a day or two once the units arrive, and the work is entirely internal, so there is no scaffolding and minimal disruption. ### What guarantee do I get? +One 10-year Swift guarantee covering workmanship and the units, with any manufacturer cover included inside those 10 years. Swift Home Improvements Ltd, company number 03679915, installing since 1998. ### Can you repair secondary glazing fitted by someone else? +We only carry out repairs on installations we originally fitted. For existing systems by others, we would quote for replacement. ### Do you cover my area? +London, Kent, Surrey, Essex and the wider South East, from our base at 215 London Road, Stone, Greenhithe. Call 01322 221010 if you are unsure about your postcode. Related ## Explore related pages Timber Windows Windows Areas we cover Contact Home Next step ## Get a fixed price for your secondary glazing in writing Director-level survey, no pressure, and a written fixed price you can compare like-for-like. We get back to you promptly. Request free quote 01322 221010 FENSA registered·10-year workmanship guarantee· London · Kent · Surrey · South East Family-run installers of bespoke windows, doors and conservatories. Serving London, Kent, Surrey & the South East since 1998. - Checkatrade 10/10 CompanyAbout - Our Work - Showroom - Trade Enquiries - Reviews - Contact Services - Windows - Composite Doors - Bi-fold Doors - Aluminium - Conservatories - Warm Roofs - Skylights & Lanterns - Orangeries - Timber Windows - Secondary Glazing - Fire Doors Get In Touch - 215 London Rd, Stone,Greenhithe DA9 9DQ - 01322 221010 - sales@swiftltd.co.ukMon–Fri · 9am–5pm Sat · By appointment © 2026 Swift Home Improvements Ltd · Company No. 03679915 · FENSA Registered Privacy Policy·Terms & Conditions·£5m Public Liability·£10m Employers' Liability CallRequest Free Quote