Basement
conversions
in Primrose Hill, NW1
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Plenty of Primrose Hill houses were built with a lower ground floor behind front railings; going deeper or further out is where Camden's basement policy begins.
Most properties here have railed front lightwells, and the statement asks for original lightwells, railings and vaults to be kept.
Across Camden, digging a basement or a lightwell has needed a planning application since 1 June 2017, when an Article 4 Direction took the permitted development right away.
Sources: Camden: Primrose Hill Conservation Area Statement (adopted December 2000, published January 2001), Camden Planning Guidance: Basements (January 2021)
Lightwells, vaults and the entrance bridge
Infilling or extending a lightwell will not normally be acceptable, and a new lightwell is unlikely to be accepted where it is not characteristic of the building or street, such as at the side of a terrace house.
A stair inside an existing lightwell may be acceptable where the group already has them and the lightwell is wide enough, built in painted metal or stone.
Infilling the area under the entrance bridge may be acceptable where that is already established in the group.
Source: Camden: Primrose Hill Conservation Area Statement (adopted December 2000, published January 2001)
Camden's basement policy
Policy A5 permits basements only where the Council is satisfied they would not harm neighbouring properties, ground and water conditions, the area's character or heritage assets.
It limits a basement to one storey, no more than half of each garden and less than one and a half times the building's footprint, and sets limits on depth from the rear and on boundaries.
Habitable rooms are not permitted in basements in areas prone to flooding.
Source: Camden Local Plan 2017
The Basement Impact Assessment
Camden requires a Basement Impact Assessment showing that the risk of damage to neighbouring properties is no higher than Burland Scale 1, very slight.
The assessment moves through five stages, from screening and scoping to site investigation, impact assessment and review, and it must include a summary a non-specialist can understand.
Its technical reports should be prepared by a chartered engineer or chartered geologist in the relevant professional body.
Sources: Camden Local Plan 2017, Camden Planning Guidance: Basements (January 2021), Camden Council: Basement developments and planning applications
Ground, water and trees
Camden's basement guidance treats ground where London Clay does not outcrop at the surface as an aquifer, and notes that springs can form where the geological layers meet.
If the basement runs out under the garden, Camden wants a metre or more of soil left on top for planting.
Trees within 10 metres of the work should be identified in the application, and those that contribute to the conservation area kept and protected.
Sources: Camden Planning Guidance: Basements (January 2021), Camden: Primrose Hill Conservation Area Statement (adopted December 2000, published January 2001)
Managing basement construction
Camden generally requires a Construction Management Plan for basement developments, and expects one where basement work is proposed in a conservation area.
Digging below and near a neighbour's foundations is work that must be notified under the Party Wall Act.
We agree spoil removal, deliveries and monitoring with the engineer and the neighbours before excavation starts.
Sources: Camden Local Plan 2017, Camden Planning Guidance: Basements (January 2021), GOV.UK: Party walls and building work
Refurbishing an existing lower ground floor
Many of these houses were built with semi-basements and raised ground floors, so a lower ground floor already exists beneath the front lightwell.
Bringing that floor up to modern standards is a different job from digging a new basement: it usually means curing damp, improving the floor, adding ventilation and replanning the rooms, with no excavation beyond the existing footprint.
We survey the existing walls and floor first, so the client can see whether a refurbishment of the lower ground floor meets the brief before any basement is considered.
Source: Camden: Primrose Hill Conservation Area Statement (adopted December 2000, published January 2001)
Depth, pools and listed houses
Camden's guidance treats one basement storey as roughly 3 to 4 metres, measured as the total external depth of the excavation.
Part of a basement may go deeper for a swimming pool only where it would not harm neighbours or the ground and water conditions.
A listed house needs listed building consent for any new basement, or to enlarge the one it has, whether or not planning permission is also required.
Source: Camden Planning Guidance: Basements (January 2021)
Where a new lightwell can go
Camden's guidance says a lightwell in a shallow front garden is likely to take most or all of it, and is unlikely to be accepted where lightwells are not part of the street.
Daylight often comes better from the side or the back, where a lightwell can open onto the garden and keep its distance from next door's boundary.
In Primrose Hill the front lightwell usually already exists, so new light is more often found at the back.
Source: Camden Planning Guidance: Basements (January 2021)
A basement conversion nearby
Questions about basements in Primrose Hill
Does a basement need planning permission in Primrose Hill?
Yes. Camden's Article 4 Direction, in force since 1 June 2017, removed permitted development for basements across the borough.
How big can a basement be?
Policy A5 limits it to one storey, no more than half of each garden and less than one and a half times the building's footprint, among other limits.
Can I add a lightwell at the side of my house?
It is unlikely to be accepted where side lightwells are not characteristic, such as on a terrace house.
What is a Basement Impact Assessment?
A staged study of the ground, water and structure that must show the risk to neighbours is no higher than Burland Scale 1, very slight.
Can I put a staircase in my front lightwell?
Possibly, where the building group already has them and the lightwell is wide enough, in painted metal or stone.
What does a basement conversion in Primrose Hill cost?
Pricing: quoted after a feasibility visit.
Sources: Camden Planning Guidance: Basements (January 2021), Camden Local Plan 2017, Camden: Primrose Hill Conservation Area Statement (adopted December 2000, published January 2001)
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Background on the streets, buildings and conservation history of Primrose Hill: The Queen’s · Sylvia Plath at 23 Fitzroy Road · The Creation of Regent’s Park · The Shakespeare Oak · The Panorama · The Lady in the Van
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