Basement
conversions
in St John's Wood, NW8
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Westminster's city-wide basement Article 4 direction has applied since 31 July 2016 and removes permitted development rights for basement development everywhere in the city.
Every basement we design in St John's Wood therefore goes to Westminster as a planning application, with its engineering and construction plan prepared alongside the drawings.
Source: Westminster City Council: Article 4 Directions in Westminster
How large Policy 50 allows
Policy 50 supports basements that extend beneath no more than 50% of the garden land.
On small sites, where the garden is 8 metres or less at its longest, a basement may reach up to 4 metres out from the original building in that direction.
The City Plan treats one storey, about 2.7 metres floor to ceiling below the lowest original floor, as the most appropriate form, with exceptions only for large sites that can take plant and construction access without harming neighbours.
The older CM28.1 basement policy is superseded; the 2026 City Plan's Policy 50 is the one we design to.
Source: Westminster City Plan 2019-2040 (2026, adopted January 2026)
Soil, drainage and trees above the basement
Policy 50 looks for at least one metre of soil, plus a drainage layer of at least 200mm, over the top of the basement.
Westminster's 2008 audit says below-ground work must allow for existing trees and leave room for new trees to grow.
The same audit notes a recent trend for subterranean extensions beneath gardens in St John's Wood.
St John's Wood houses usually sit in large plots with generous gardens, so the garden design, the soil depth and the tree protection are drawn into the basement scheme from the start.
Sources: Westminster City Plan 2019-2040 (2026, adopted January 2026), Westminster City Council: St John's Wood Conservation Area Audit SPD
Heritage, lightwells and plant
Basements should protect heritage assets and, in a listed building, not upset the original hierarchy of spaces where that matters to its significance.
Lightwells, plant, vents, skylights and means of escape should be sensitively designed and discreetly placed, so the building, its garden setting and the area are conserved.
Where a basement runs under the pavement, Policy 50 limits it to 1.8 metres under the highway, with at least 900mm between the road surface and the vault.
Source: Westminster City Plan 2019-2040 (2026, adopted January 2026)
What goes with the application
A structural methodology statement is required for every basement in Westminster.
In flood zone 2 or 3, or a surface water flood risk hotspot, a site-specific Flood Risk Assessment and a structural statement are also needed.
A signed Appendix A of the Code of Construction Practice should be submitted with the application, and Westminster strongly encourages talking to neighbours before applying.
Source: Westminster City Plan 2019-2040 (2026, adopted January 2026)
Starting from the lower ground floor you have
Westminster's audit describes most houses here as two or three storeys standing over a basement.
So the first question on many St John's Wood jobs is not whether to dig, but how much more the existing lower floor can give. Lowering its floor slightly, opening its front vaults and adding a lightwell at the back can turn a dark service floor into rooms people want to use, often without new excavation under the garden.
We survey that floor first, measure its headroom, find the foundation depths of the walls around it and price the refurbishment before any larger scheme is drawn.
Source: Westminster City Council: St John's Wood Conservation Area Audit SPD
What the rooms below a villa are used for
Clients here usually ask for a family room or playroom that can be closed off, a guest bedroom with its own shower room, a gym, or a utility room with laundry, boot storage and space for the boiler and water cylinder.
Bedrooms below ground need daylight, ventilation and a safe way out, so they sit against a lightwell; rooms without windows are better given to storage, plant and laundry. We arrange the plan so the stair arrives in the middle, with the noisy rooms away from the neighbours' walls.
Keeping a basement dry
Waterproofing is designed to BS 8102 from the outset. Most of our basements combine a structural concrete box with a drained cavity membrane inside it, which carries any water that gets through to a sump and a pump with a battery backup.
The pump, its alarm and the inspection points stay accessible after the rooms are finished, and we hand over a maintenance schedule so the system keeps working for the life of the building.
Westminster's Code of Construction Practice
Projects that build a basement and are not Level 1 or Level 2 fall into the Code's Level 3.
A Level 3 project prepares a Construction Management Plan covering environmental management, training and community engagement, and submits Checklist B with it.
The programme depends on the agreed scope, approvals, site conditions and procurement. Discuss the sequence of work at a feasibility visit.
Work, including site preparation, does not start until the plan has been approved.
Source: Westminster City Council: Code of Construction Practice (May 2026)
Section 61 and working hours on a basement
Noisy work outside the set hours needs prior consent under Section 61 of the Control of Pollution Act 1974, Westminster's Code says.
On a Level 3 project without that consent, the contractor is served a Section 60 notice setting the working hours before work starts.
Construction traffic, including lorries collecting spoil, keeps to the agreed site hours unless the council agrees otherwise.
Source: Westminster City Council: Code of Construction Practice (May 2026)
Excavation days and neighbours
Westminster does not permit demolition, excavation or piling on Saturdays without special permission.
A building owner proposing work under the Party Wall etc Act 1996 must give the adjoining owners notice in the way the Act sets down.
Before skips or heavy equipment stand over vaults beneath the pavement, those structures need careful consideration.
Spoil removal is the heaviest part of a basement job, so lorry times, conveyors and parking bays are agreed in the construction plan before excavation begins.
Sources: Westminster City Council: noise problems we can investigate, GOV.UK: Party Wall etc. Act 1996 guidance, Westminster City Council: Code of Construction Practice (May 2026)
A St John's Wood villa we have worked on
Questions about basements in St John's Wood
Is a basement permitted development in St John's Wood?
No. Westminster's city-wide Article 4 direction has removed basement permitted development rights since July 2016.
How much of my garden can a basement go under?
Policy 50 supports basements under no more than 50% of the garden land, with a 4 metre limit on small sites.
Can I build two storeys down?
The City Plan prefers one storey, about 2.7 metres floor to ceiling, with exceptions only for large sites.
What documents does Westminster need?
A structural methodology statement, a signed Code of Construction Practice Appendix A and, in flood risk areas, a Flood Risk Assessment.
Can excavation happen on Saturdays?
Not without special permission: Westminster does not permit demolition, excavation or piling on Saturdays.
What does a basement conversion in St John's Wood cost?
Pricing: quoted after a feasibility visit.
Sources: Westminster City Council: Article 4 Directions in Westminster, Westminster City Plan 2019-2040 (2026, adopted January 2026), Westminster City Council: noise problems we can investigate
Related pages
Sources
- Westminster City Council: Article 4 Directions in Westminster
- Westminster City Plan 2019-2040 (2026, adopted January 2026)
- Westminster City Council: St John's Wood Conservation Area Audit SPD
- Westminster City Council: Code of Construction Practice (May 2026)
- Westminster City Council: noise problems we can investigate
- GOV.UK: Party Wall etc. Act 1996 guidance
More Services in St John's Wood
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St Johns Wood history & architecture
Background on the streets, buildings and conservation history of St Johns Wood: Avenue Road History · How St John's Wood Became NW8
Completed renovation project examples
