City of Westminster

Adopted Documents We Assess Against

Development plan: Westminster City Plan 2019-2040 (adopted 21 April 2021)

Documents are re-checked against the council's own website weekly. A detected change flags "Policy Update Available" for human review — live assessment standards are never replaced automatically.

City of Westminster standards at a glance

5 numeric standards taken from City of Westminster's own adopted documents, each shown with the paragraph it comes from. Figures differ between councils — these are this one's.

Roof form

up to 70°

The council expects a mansard principal slope no greater than 70 degrees. Westminster Roofs SPG (provisional citation)

up to 30°

The council expects a mansard upper slope not normally greater than 30 degrees. Westminster Roofs SPG (provisional citation)

up to 2.3

The council sets a normal maximum floor-to-ceiling height of 2.3m within a mansard. Westminster Roofs SPG (provisional citation)

Basement

up to 50%

A Westminster basement can sit under half the garden - and "garden" means everything on the plot that is not the original house, including paving and the side return. If your garden is 8 metres or shorter you get a different test: 4 metres out from the building. Westminster City Plan Policy 50(B)(1)

at least 1m

A metre of soil over a Westminster basement, with 200mm of drainage on top of that - so about 1.2 metres in total before you reach the basement roof. Westminster City Plan Policy 50(B)(4)

Standards are what the council normally expects, not a guarantee. A scheme outside them can still be approved on its merits, and one inside them can still be refused for another reason.

Authored Policy Library

9 local policy checks, each citation-locked to the adopted document. National policy (NPPF, national space and daylight standards) applies alongside these.

Westminster City Plan 2019-2040

• Westminster City Plan Policy 38 — Design character Westminster will judge how well your proposal fits its surroundings and the quality of its materials. Expect a high bar - much of the city is conservation area, and design is assessed strictly.
• Westminster City Plan Policies 7 and 33 — Amenity neighbouring (provisional citation) Westminster will look closely at the effect on your neighbours' light and outlook. Where a proposal comes near a neighbouring window, a daylight and sunlight report is often expected.
• Westminster Roofs SPG — Roof form (3 checks) (provisional citation) The council expects a mansard principal slope no greater than 70 degrees. The council expects a mansard upper slope not normally greater than 30 degrees. The council sets a normal maximum floor-to-ceiling height of 2.3m within a mansard.
• Westminster adopted guidance, read 2026-08-05 — Rear extension depth Westminster set no depth or height figures for extensions. There is no number to design to - the case turns on how the extension sits against the building and the conservation area, and on daylight to neighbours.

Westminster SPG: Roofs - a guide to alterations and extensions on domestic buildings

• Roofs SPG section 5 (General Rules; Dormer Design; Roof Terraces) — Roof form Westminster's householder guidance is almost all about roofs. A mansard runs at up to 70 degrees with a 30-degree upper slope and about 2.3 metres of headroom, and dormers are sized against the windows below rather than to a set dimension. The guide is old, so check it against the current City Plan.

Westminster City Plan 2019-2040 (consolidated January 2026)

• Westminster City Plan Policy 50(B)(1) — Basement A Westminster basement can sit under half the garden - and "garden" means everything on the plot that is not the original house, including paving and the side return. If your garden is 8 metres or shorter you get a different test: 4 metres out from the building.
• Westminster City Plan Policy 50(B)(4) — Basement A metre of soil over a Westminster basement, with 200mm of drainage on top of that - so about 1.2 metres in total before you reach the basement roof.