FAQs

Yes. Original timber sash windows can take slimline vacuum double glazing in the existing sashes. The glazing rebate is deepened on the outside face, the new unit is bedded and puttied, and the sash goes back into the same box frame. From the street the window looks as it did; from inside you notice the quiet and the warmer glass.

Yes, and it is what this service exists for. Sash and casement windows made in the Georgian, Victorian and Edwardian periods were built with thin glazing rebates because glass was thin. A vacuum unit at 6.7 mm is close enough to the original pane thickness to fit those rebates once they are carefully deepened, so the window keeps its glazing bars, its putty line and its proportions.

Box sash windows, casements, French doors and fixed lights in timber. Rectangular panes are the norm; curved, arched, trapezoid and oval panes are made to template — see special shapes. Metal and uPVC windows are outside the scope of this service.

London postcodes. Send your postcode with the enquiry and we will confirm before booking a survey.

Two parts. The glass is made to measure after the survey and takes roughly four to six weeks to arrive. The fitting itself is done from a mobile workshop outside the house: sashes come out in the morning and go back in the same evening, so no window is left open overnight. How many windows are done per day depends on their size and condition — the survey visit gives you a realistic programme.

No. The sashes are taken out through the window opening and worked on outside. We ask for clear access to each window inside (a metre or so of floor space) and somewhere to park the workshop van. Curtains and blinds near the windows are best taken down for the day.

Use the contact form with your postcode, the number of windows and their style, or call. Quotes are per window after a survey, because the price depends on size, glazing bars, the condition of the timber and access. There are no fixed price lists on this site for that reason — what affects the cost explains the factors.

The unit we fit is vacuum insulated glazing: two panes of glass with a gap of a fraction of a millimetre between them, from which the air has been pumped out. Without air there is almost no conduction or convection across the gap, so a unit under 7 mm thick insulates better than a conventional 28 mm double-glazed unit. It fits directly into the old sash where a single pane used to sit.

The U-value is the rate at which heat passes through the glass, in watts per square metre per degree of temperature difference. Lower is better. Single glazing is around 5.7–5.8 W/m²K; a vacuum insulated glazing unit is around 0.7 W/m²K (manufacturers’ centre-of-glass figures). Both numbers describe the glass itself, not the whole window with its frame.

Not from a normal viewing distance. The glazing bars, sightlines and putty finish are kept, and the unit is thin enough to sit in a deepened version of the original rebate. Up close, a vacuum unit has a grid of tiny support pillars (each well under a millimetre across, roughly 20 mm apart) that hold the two panes apart; you can find them if you look for them against a bright sky. Reflections are slightly stronger than single glass, as with any double glazing.

No window is soundproof, but the change from a single 3–4 mm pane to a sealed two-pane unit is large, and the draught-proofing seals fitted at the same time close the gaps that let most of the noise in. If traffic or aircraft noise is the main reason for the work, say so at the survey — the seal specification matters as much as the glass.

Often, but it is a case-by-case decision for the conservation officer, and reglazing a listed window normally needs listed building consent because it alters the building’s fabric. Historic England’s guidance treats slim and vacuum glazing in existing frames as something that can be acceptable where the sightlines, glazing bars and putty finish are kept. We can supply drawings and a sample for the application, but we do not promise consent. See listed buildings & conservation areas.

Replacing the glass in an existing frame is not a “controlled fitting” under Approved Document L, so the energy-efficiency rules that apply to replacement windows are not triggered, and no trickle vents are required. Replacing the whole window is different and does fall under Part L.

Some manufacturers make tempered vacuum units. The units normally fitted are annealed glass; where safety glazing is required — glass close to floor level or beside a door — we discuss the options at the survey rather than assume.

Vacuum insulated glazing, at roughly 6–8 mm overall depending on the maker (6.7 mm for the unit in the comparison chart on the slimline page). Slim gas-filled units are around 11 mm and standard double glazing 24–28 mm. Thickness is what decides whether a unit can go into an original sash without rebuilding it.

Yes. A vacuum unit weighs about twice as much as the single 3–4 mm pane it replaces. Sash windows are counterbalanced, so the weights in the box are increased to match (typically by around a third) and the cords are renewed at the same time. Old sashes are repaired and strengthened before the glass goes in.

Manufacturers publish long service-life figures for vacuum units and back them with warranties; independent, long-term field data at scale is still limited because the product is comparatively new in the UK. Ask for the manufacturer’s warranty terms in writing with your quote and keep them with the paperwork.

Each sash is re-hung on new cords with the weights adjusted, the new putty is left to skin over, and the exterior is primed and painted. You can open and close the windows straight away; the putty and paint reach full hardness over the following weeks, so avoid pressure-washing the outside during that time.

Exactly like ordinary glass: water and a little detergent, or a standard glass cleaner, with a soft cloth or squeegee. Do not use abrasive pads or razor blades on the panes, and keep solvents off the putty and paint.

Yes — timber windows need repainting every few years whatever the glass, and keeping the exterior paint and putty sound is what protects the frame and the unit’s edge. Reglazing reduces internal condensation on the glass, which is one of the main causes of paint failure on the inside of old windows, so the inside face tends to need less attention than before.

A broken pane is replaced like any other: the unit is measured, a new one made and fitted into the same rebate. Manufacturing faults are covered by the manufacturer’s warranty (the terms come with your quote). Accidental breakage is usually a matter for home insurance, as with any glazing.

The seals are fitted as part of the reglazing because the sashes are already out and the grooves are cut then. If you have windows that are not being reglazed, they can be draught-proofed on their own — see draught-proofing.