Basement
conversions
in Maida Vale, W9
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Many Maida Vale houses already stand on a lower floor, and Westminster's Policy 50 decides how much further down, and how far under the garden, a basement can go.
Since July 2016 Westminster's Article 4 direction has taken basement development out of permitted development everywhere in the city, so a new basement always needs planning permission.
Every W9 basement enquiry opens with the ground: a desk study and the sewer records first, then trial pits and boreholes if the idea survives.
Source: Westminster City Council: Article 4 Directions in Westminster
How far a basement can extend
Under Policy 50 a basement should occupy no more than half the garden land; in a garden 8m or less at its longest, it may reach 4m out from the original house in that direction.
An untouched strip of garden, proportionate to the scheme and the plot, should be left all round the site boundary.
Westminster's preferred depth is one storey, roughly 2.7m from floor to ceiling, beneath the lowest original floor, with exceptions confined to large sites that construction traffic can reach easily.
Above the basement there should be a metre or more of soil over a drainage layer of at least 200mm, rising to as much as 1.5m where trees will grow.
Enlarging a basement that already exists falls under the same policy as digging a new one.
When the house already has a cellar or a lower ground floor, lowering and lining that space is the first option we cost.
Source: Westminster City Plan 2019-2040 (2026, adopted January 2026)
Water under W9
The Bayswater Rivulet was culverted in the mid 19th century and has vanished from street level, the conservation area directory notes.
Basements can flood from overflowing drains or nearby watercourses, from groundwater and from surface water, the City Plan warns.
Sites in flood zone 2 or 3, or in a surface water hotspot, need their own Flood Risk Assessment and a structural statement.
Expected safeguards include sustainable drainage and positive pumped devices, or an equivalent, against sewer surcharge.
We design the sump, pumps, non-return valves and the drained membrane as part of the structure, with hatches left for servicing.
Sources: Westminster City Council: Maida Vale Conservation Area directory (scanned PDF; quotes transcribed), Westminster City Plan 2019-2040 (2026, adopted January 2026)
Listed houses and the order of rooms
A new lower floor can upset the way a historic house's rooms are ranked, the City Plan cautions.
Lightwells, plant, vents, rooflights and escape routes should be discreet and sensitively designed.
Listed building consent for excavation or major structural work needs a structural survey or methodology statement with it.
Below a listed house the new stair is kept apart from the original staircase, and lightwells go to the rear where they are seen least.
Sources: Westminster City Plan 2019-2040 (2026, adopted January 2026), Westminster City Council: Listed building consent
The garden above
A basement application should come with a landscaping plan of planting, soft landscaping and permeable surfaces.
A large part of the garden is to stay undeveloped and free of impermeable surfacing, so it drains and keeps its setting.
Pruning or removing a protected tree without consent or notice is a criminal offence.
The garden's levels and planting are surveyed before the dig, so it can be rebuilt as it was or better.
Sources: Westminster City Plan 2019-2040 (2026, adopted January 2026), Westminster City Council: Trees and high hedges
Preparing the application
All basement proposals in Westminster need a structural methodology statement, plus a signed Appendix A from the Code of Construction Practice.
The council strongly encourages a conversation with neighbours before submitting, and may ask for evidence of it along with a timetable of the works.
Under the pavement a basement may reach no further than 1.8m, keeping at least 900mm between the surface and any vault.
The engineer's statement, the construction plan and the pack for neighbours are written together, so all three describe the same excavation.
Source: Westminster City Plan 2019-2040 (2026, adopted January 2026)
Digging safely next door to neighbours
Under Westminster's Code of Construction Practice, a basement job that is not Level 1 or 2 is Level 3 and needs a Construction Management Plan.
The programme depends on the agreed scope, approvals, site conditions and procurement. Discuss the sequence of work at a feasibility visit.
Excavation is barred on Saturdays unless special permission has been given.
Any vault beneath the pavement has to be considered before a skip or heavy plant is set down above it.
Excavating close to and below a neighbour's foundations triggers party wall notice.
Muck-away drives the whole site plan: conveyor positions, skip swaps and lorry slots are agreed with the neighbours before the first spade goes in.
Sources: Westminster City Council: Code of Construction Practice (May 2026), Westminster City Council: noise problems we can investigate, GOV.UK: Party walls and building work
Questions about basements in Maida Vale
Is planning permission needed for a Maida Vale basement?
Always. Westminster's city-wide Article 4 direction took away permitted development rights for basements in 2016.
What depth will Westminster accept?
One storey, about 2.7m floor to ceiling, beneath the lowest original floor.
What share of the garden can a basement take?
Half of the garden land at most, with an undeveloped margin all round the boundary.
Is there a buried stream in Maida Vale?
Westminster's directory says the Bayswater Rivulet was culverted in the mid 19th century and cannot be seen from the street.
Can digging happen at weekends?
Not on Saturdays, unless Westminster grants special permission.
What does the Code of Construction Practice add?
A basement job is usually Level 3, which brings a Construction Management Plan.
Sources: Westminster City Council: Article 4 Directions in Westminster, Westminster City Plan 2019-2040 (2026, adopted January 2026), Westminster City Council: Maida Vale Conservation Area directory (scanned PDF; quotes transcribed), Westminster City Council: noise problems we can investigate, Westminster City Council: Code of Construction Practice (May 2026)
Related pages
Sources
- Westminster City Council: Article 4 Directions in Westminster
- Westminster City Plan 2019-2040 (2026, adopted January 2026)
- Westminster City Council: Maida Vale Conservation Area directory (scanned PDF; quotes transcribed)
- Westminster City Council: Listed building consent
- Westminster City Council: Trees and high hedges
- Westminster City Council: Code of Construction Practice (May 2026)
- Westminster City Council: noise problems we can investigate
- GOV.UK: Party walls and building work
Guides & Local Reading
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Maida Vale history & architecture
Background on the streets, buildings and conservation history of Maida Vale: Maida Vale's Mansion Blocks · Formosa Street: The Village High Street of Little Venice