Sash window double glazing without replacement.

We retrofit vacuum-insulated glass into your existing sashes — no replacement, no compromise on the original look.

What it is.

Vacuum-insulated glass units fitted into your existing sash frames. The window stays in place — only the glass changes.

U-value drops from ~5.0 down to ~0.7 W/m²K — triple-glazed performance in an 8 mm unit.

The sash, the sightline, the joinery — all original.

Single glazing removed; frames rebated to take the new glass.

The numbers.

Single glazing

5.0 W/m²K

VIG glazing

0.7 W/m²K

↑ 4.3 W/m²K less than single glazing

U-value — lower is better. The amount of heat lost per square metre per degree of temperature difference.

Why VIG, not standard double glazing.

VIG — vacuum-insulated glass — is two panes of glass held a fraction of a millimetre apart by tiny invisible spacers, with a vacuum sealed between them. A vacuum is the highest-spec insulation that exists; no air or gas can carry heat across it. Standard double-glazing units use a 16–20 mm sealed cavity filled with air or argon. VIG outperforms them in a 6–8 mm unit, which is the only reason it can be retrofitted into an original sash without changing the look of the window.

01

Slim profile

8 mm — about a third of a standard double-glazed unit. The heritage sightline stays exactly as it was; no chunky reveal around the glass.
02

Vacuum cavity

The highest-spec insulation available — matches triple-glazed performance in a retrofit unit. Glass surface stays warm to the touch in winter.

Loses less heat than the walls.

A retrofitted sash has a lower U-value than the brick wall it sits in. Under a thermal camera, that means the window reads cooler (darker) than the surrounding walls — heat is now leaving through the wall, not the glass.