Basement conversions near South End Green and Parliament Hill
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Basement work near South End Green and Parliament Hill begins with the ground: Camden's screening for the Heath Ponds catchment, a Basement Impact Assessment and Policy A5's limits on size.
Near the Heath, Camden's screening process calls for a hydrogeological assessment when the geology, the Hampstead Heath Ponds catchment or any planned dewatering comes into play.
For a basement near the Heath we therefore commission ground and water investigation before any layout is drawn.
Source: Camden Planning Guidance: Basements (January 2021)
Groundwater, Springs and Clay
Camden's guidance counts the Claygate Member, the Bagshot Formation and other ground where London Clay is not the top layer as aquifers.
Springs can rise at the junctions between those layers: Bagshot over Claygate, and Claygate over London Clay.
A basement in a flood-prone location cannot hold bedrooms, living space or other sensitive uses, Camden says.
We plan trial holes and groundwater monitoring with the engineer so that readings cover more than one season where the design depends on them.
Sources: Camden Planning Guidance: Basements (January 2021), Camden Local Plan 2017
What Policy A5 Allows
Policy A5 tests a basement against harm to neighbours, to structural, ground and water conditions, to the area's character and amenity, to the host building's architecture and to heritage assets.
It allows one storey only, never under an existing basement, with no more than 50% of any garden used and a footprint below 1.5 times that of the house.
A deeper section for a swimming pool is possible only if it harms neither neighbours nor ground and water conditions and the extra depth holds nothing but the pool.
Sources: Camden Local Plan 2017, Camden Planning Guidance: Basements (January 2021)
The Basement Impact Assessment and the Burland Scale
Camden sets out five stages for the assessment, starting with screening and scoping and ending with review and a decision, with site investigation and the impact assessment between.
Predicted damage to nearby buildings is graded on the Burland Scale, which ranks cracking by how readily it could be put right.
The authors should be engineers or chartered geologists belonging to their professional body.
Sources: Camden Planning Guidance: Basements (January 2021), Camden Council: Basement developments and planning applications
Lightwells and Gardens
At the front, Camden warns that a lightwell can swallow a shallow garden and is unlikely to be accepted in a street that has none.
At the side or back, a lightwell can bring daylight and a way out to the garden, provided it stays clear of the boundary with next door.
Under the garden, a basement that runs beyond the house needs a metre of soil over it, Camden says, for planting and to limit the effect on infiltration.
Source: Camden Planning Guidance: Basements (January 2021)
Listed Buildings and Pre-Application Advice
Under a listed building, digging a basement or enlarging basement rooms that already exist always calls for listed building consent, whatever the planning position.
Camden's more detailed tier of homeowner pre-application advice is the one that covers basement schemes.
The assessment should start with a summary written for readers without technical training.
Sources: Camden Planning Guidance: Basements (January 2021), Camden Council: Pre-planning application advice for homeowners
Construction Management and Neighbours
Camden normally asks for a Construction Management Plan on basement schemes, and expects a demolition or construction management plan for basement works in a conservation area or next to a listed building.
Digging below and near the foundations of a neighbouring property is party wall work that requires notice to the neighbour, GOV.UK says.
We share the construction programme and the monitoring arrangements with the neighbours before excavation starts.
Sources: Camden Local Plan 2017, Camden Planning Guidance: Basements (January 2021), GOV.UK: Party walls and building work
Basement projects we have completed nearby
Questions about a basement near the Heath
Will a hydrogeological assessment be required?
Where Camden's screening points to the geology or the Hampstead Heath Ponds catchment, yes.
How big can a basement be under Policy A5?
A single storey, not beneath another basement, using at most half of each garden and with a footprint under 1.5 times the house's.
Can a basement include a swimming pool?
Camden allows extra depth for a pool only where it causes no harm to neighbours or to ground and water conditions and is used only for the pool.
Who prepares the Basement Impact Assessment?
engineers or chartered geologists who are members of the relevant professional body.
Is a construction management plan needed?
Normally, for any basement in Camden, and especially in a conservation area or beside a listed building.
Sources: Camden Planning Guidance: Basements (January 2021), Camden Local Plan 2017, Camden Council: Basement developments and planning applications
Basements near South End Green and Parliament Hill
Camden's basement Article 4 direction applies to the whole borough, so every basement excavation needs planning permission. For a new or extended basement, Camden asks for a Basement Impact Assessment specific to the site that assesses the effect on drainage, flooding, groundwater conditions and structural stability.
The Hampstead Neighbourhood Plan, adopted by Camden on 21 July 2025, reaches South End Green. It explains that hard standing and larger building footprints on Hampstead's sloping streets add surface run-off, increasing flood risk in storm periods for lower areas such as South End Green and Fleet Road. Its Policy BA1 asks basement proposals for a construction method posing a risk of damage to neighbouring properties no higher than Burland Scale 1, 'very slight', and requires new basements connected to the sewer network to be fitted with a positive pumped device or similar against sewer flooding.
On South Hill Park, in the same conservation area as Parliament Hill, Camden's statement records that the 1988 designation report noted public concern about excessive excavation at the rear of a house backing onto the No.1 pond, and it lists the excavation of basement areas for additional accommodation among the pressures that followed the conversion of houses to flats.
Sources: Camden Council — Article 4 directions for other development (basements); Camden Council — Basement developments and planning applications; Camden Council — Hampstead Neighbourhood Forum and Neighbourhood Plan page; Hampstead Neighbourhood Plan 2025–2040, as adopted by Camden Council; Camden Council — South Hill Park Conservation Area Statement (scanned PDF; quotes transcribed from the page images, printed page numbers)
For homes in Hampstead village itself, see basement conversions in Hampstead, NW3.
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