Conservation Window Trends in London Boroughs (2026)

London's conservation-area coverage is extensive: the majority of pre-1939 housing in the inner boroughs sits inside a designated area, an Article 4 direction, or a listing. The practical consequence for 2026 is that window projects are judged on reversibility rather than on performance claims.

The reversibility test

Internal secondary glazing is treated as a permitted internal alteration in nearly every London borough we work in, provided three conditions hold: the unit is removable without trace, no original timber is cut or damaged, and internal visual impact is minimal. That test — not U-values or dB figures — decides approval. The reasoning is set out in our listed buildings guide and in secondary glazing vs double glazing for listed buildings.

Borough-level patterns we see

Camden (Hampstead, Highgate, Primrose Hill) is among the most active conservation teams in London; replacement windows are routinely refused, while internal reversible units pass without issue.

Kensington & Chelsea and Westminster focus on street-level appearance: slimline profiles invisible from the pavement, and colour-matched frames on principal elevations.

Islington applies Article 4 directions widely across its Georgian terraces, with attention to sash proportions and glazing-bar alignment.

Richmond upon Thames combines conservation control with heavy Heathrow flight-path noise exposure, which makes acoustic secondary glazing the standard recommended route.

Trend: documentation before installation

Owners increasingly ask for a written specification and photographic method statement showing fixings into the reveal rather than the original frame. For Grade II* and Grade I properties, or anything in sight of a listed frontage, we advise a courtesy notification to the conservation officer even where strict consent is not required. The thresholds are covered in the planning permission guide.

Trend: colour matching over concealment

The move away from white-only frames continues. RAL-matched powder coating to existing period joinery makes the internal unit read as part of the reveal, which is exactly what conservation officers respond well to. Format options are on our vertical sliding and horizontal sliding pages.

What it costs and where to start

Heritage-specification London projects typically run £1,100–£1,700 per window installed in the central boroughs, with survey, bespoke manufacture and installation included. Compare local figures on our London district guides or get a project-specific range from the estimator.