Replacing Windows in London: What Requires Planning Permission

Replacing windows seems like a straightforward project — but in London, planning rules can make it more complicated than expected. Conservation areas, Article 4 directions, and listed building status all impose restrictions that don't apply in ordinary residential areas.

Standard Residential Properties (Not Listed, Not in Conservation Area)

Replacing like-for-like windows in standard residential properties is permitted development — no planning permission is required, provided:

• The replacement window does not project beyond the plane of the outer wall
• The material, colour, and size are broadly similar to the original

This applies to both the front and rear of the property.

Building Regulations note: Window replacement does require Building Regulations compliance for thermal performance (Part L). Replacement windows must meet minimum U-value requirements. Most professional window installers register the installation under a competent person scheme (FENSA or equivalent), which self-certifies compliance.

Conservation Areas

In conservation areas, planning restrictions on windows depend on whether an Article 4 direction is in place:

Conservation area without Article 4: Window replacement is still technically permitted development — but the Local Planning Authority can still take enforcement action if they believe the replacement harms the character of the conservation area (though this is less common).

Conservation area with Article 4 direction on windows: Planning permission is required for replacement windows. Article 4 directions specifically protecting windows are common across London conservation areas — they are used to prevent UPVC or aluminium window replacement on Victorian and Edwardian terraces where timber sash windows are part of the character.

How to check: Search your address on the council's interactive planning map, or call the planning department.

What Planning Will Typically Require in Conservation Areas

In conservation areas where planning permission is required for window replacement:

• Timber sliding sash windows (matching the original form and proportions) are almost always acceptable
• UPVC windows are almost always refused in conservation areas
• Aluminium windows in a slim-profile system may be acceptable in some conservation areas but not all
• Double-glazed units are generally acceptable if the window frame matches the original form and proportions
• Secondary glazing (a separate inner window) is a common alternative to full replacement for listed buildings

Listed Buildings

In listed buildings, planning permission AND Listed Building Consent are required for window replacement. The consent process assesses whether the replacement is appropriate to the character of the listed building. Original sash windows in listed buildings are often considered an integral part of the significance of the building — replacing them with double glazing may be refused or permitted only with specialist slim-profile double-glazed sash units.

RCB Design & Build

RCB Design & Build advises on window replacement planning requirements as part of refurbishment projects — and coordinates planning and Listed Building Consent applications where required.