Secondary Glazing for Victorian Terraces

Draughts come from shrunk timber and worn parting beads. Noise comes from 4mm glass plus perimeter leakage. Cold comes from a U-value around 5.0 W/m²K on single glazing — worse than an uninsulated brick wall.

A single secondary system addresses all three: the sealed cavity stops air movement, the acoustic laminate blocks sound, and the trapped air layer drops the U-value to roughly 1.8 W/m²K.

The Victorian bay is the technically demanding part of any terrace project. Angled returns mean the secondary frames must be mitred to the bay geometry rather than fitted as three independent rectangles, or you get visible gaps at the corner joints.

We survey bays with a laser to capture the actual internal angles, which in a settled terrace are rarely the nominal 45 or 90 degrees.

Most owners start with the two front bedrooms and the front reception — the rooms where street noise costs sleep and quiet. Rear elevations and the return can follow later; because each unit is independent, there is no penalty for phasing.

A typical London Victorian terrace presents four different window conditions in one house: a canted or square bay to the front reception, standard sashes to the upper floors, a narrow half-landing window over the return, and often a later casement or door to the rear extension. Treating them as one order is why generic quotes go wrong. Each needs its own reveal measurement, opening style and, frequently, a different glass thickness depending on which elevation faces the road.

Front elevations on a bus route or through-road carry the noise; rear elevations facing gardens usually do not. Spending the acoustic budget where the noise actually is — 10.8mm laminate to the front, 6.4mm to the rear — typically saves a meaningful share of a whole-house cost without any perceptible loss.

Most terrace owners phase the work. The usual order is street-facing bedrooms first, then the front reception, then the remaining rooms as budget allows. Because every frame is made to the same system and finish, a phase two eighteen months later matches phase one exactly — we keep the specification and colour reference on file against the address.

Installation is disruptive for hours rather than days. A four-window front elevation is normally a single day with two fitters, working from inside only, with no scaffolding and no external access required. That matters in terraces where there is no side return and the front is directly on the pavement.

Victorian terraces are solid-walled, so the windows are rarely the coldest surface in the room once secondary glazing is in — but before it goes in they usually are, which is why condensation and mould gather on reveals and in corners near the window. Sealing the window layer raises the internal surface temperature and moves the dew point away from the glass.

It does not remove moisture from the house. Where a terrace has a drying-laundry or bathroom-extract problem we say so at survey and recommend ventilation changes alongside the glazing, because a sealed window in an under-ventilated room simply moves the condensation to the next coldest surface. Whole-house terrace work is delivered through our residential secondary glazing service.