Basement
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in Swiss Cottage, NW3
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A Swiss Cottage basement is decided by Camden's Policy A5 and by the water that still runs beneath these slopes, so the ground is studied before any room is drawn.
The Fitzjohns/Netherhall appraisal records that its streets were laid over feeder streams of the Fleet, Tyburn and Westbourne, which now flow underground.
Every basement enquiry we take in Swiss Cottage starts with an engineer's desk study and the plot's history, and only after that do we say whether a basement is realistic.
Source: Camden: Fitzjohns/Netherhall Conservation Area Character Appraisal and Management Plan (December 2022)
What Camden Local Plan Policy A5 allows
Policy A5 of Camden's 2017 Local Plan is the test: a basement is allowed only once the council is satisfied that neighbouring houses, the ground and groundwater, the street's character and the host building will come to no harm.
The same policy caps a Swiss Cottage basement at one storey, never beneath an existing basement, under half of each garden, below 1.5 times the footprint of the house and stepped back from neighbouring boundaries.
Camden's guidance treats that single storey as an excavation of about 3 to 4 metres, measured on the outside.
Its Basement Impact Assessment has to show damage to neighbours no worse than Burland category 1, very slight.
Sources: Camden Local Plan 2017, Camden Planning Guidance: Basements (January 2021)
Why every basement here needs an application
Since 1 June 2017 a Camden Article 4 Direction has removed permitted development for basements, so digging any basement or lightwell in the borough now means a planning application.
If the house is listed, a new or extended basement also requires listed building consent.
In the Elsworthy Conservation Area, which takes in houses along King Henry's Road, the council normally resists basements that front the road.
Near Fitzjohn's Avenue, extending into basement areas is acceptable only without harm to the house or its setting, keeping lightwells minimal and leaving enough topsoil for planting.
Sources: Camden Planning Guidance: Basements (January 2021), Camden: Elsworthy Road Conservation Area Appraisal and Management Strategy (adopted 14 July 2009), Camden: Fitzjohns/Netherhall Conservation Area Character Appraisal and Management Plan (December 2022)
Ground and water under Swiss Cottage
Camden's appraisal follows the River Tyburn from under Shepherd's Well, through conduits past Swiss Cottage, Regent's Park Lake and Buckingham Palace, down to the Thames.
Its basement guidance counts any ground where London Clay is not at the surface as an aquifer, including the Claygate Member and the Bagshot Formation.
Modelling quoted there shows parts of South Hampstead, West Hampstead and Hampstead Town at greater risk of surface water flooding.
In flood-prone ground, Camden refuses basements containing bedrooms or other habitable rooms.
Sources: Camden: Fitzjohns/Netherhall Conservation Area Character Appraisal and Management Plan (December 2022), Camden Planning Guidance: Basements (January 2021), Camden Local Plan 2017
Lightwells, railings and front gardens
According to the Elsworthy strategy, a new lightwell can weaken the tie between a house and its street and eat into the garden, and railings round it clutter the frontage.
Glazed panels let into a front garden over a basement can leak light and spoil the garden's setting.
Camden's basement guidance warns that in a shallow front garden a lightwell is likely to swallow most of it, and favours side or rear lightwells kept off the neighbouring boundary.
On King Henry's Road the appraisal records basement areas and boundary walls lost to sloping parking bays at Nos 135 and 139.
Sources: Camden: Elsworthy Road Conservation Area Appraisal and Management Strategy (adopted 14 July 2009), Camden Planning Guidance: Basements (January 2021)
Houses that already have a lower floor
A lot of local houses have one: King Henry's Road townhouses are often raised on semi-basements, and buildings on Fellows Road and Winchester Road commonly rise three storeys over a basement.
With A5 ruling out a basement beneath an existing basement, houses that have one are usually better served by improving the lower floor they already have.
Upgrading an old cellar or semi-basement involves tanking, a new slab, insulation and better light, and we survey it with the same care as a new excavation.
Sources: Camden: Elsworthy Road Conservation Area Appraisal and Management Strategy (adopted 14 July 2009), Camden: Belsize Conservation Area Statement (agreed 20 November 2002), Camden Local Plan 2017
Gardens and trees over a basement
Where the basement runs out under the garden, Camden expects at least a metre of soil on top so planting can grow.
Lightwells and swimming pools both appear on the Fitzjohns/Netherhall appraisal's list of causes of lost back garden.
Works to trees in that conservation area must be notified to Camden, and many of them have preservation orders requiring consent.
The Belsize statement asks applicants on Eton Avenue and Fellows Road to identify trees within 10 metres of underground works.
Sources: Camden Planning Guidance: Basements (January 2021), Camden: Fitzjohns/Netherhall Conservation Area Character Appraisal and Management Plan (December 2022), Camden: Belsize Conservation Area Statement (agreed 20 November 2002)
The Basement Impact Assessment
Camden's assessment moves through five steps: screening, scoping, site investigation and study, impact assessment, and review.
Its technical chapters are written by a chartered engineer or chartered geologist, and a plain summary sets out the findings for readers with no engineering background.
We commission the boreholes and the groundwater readings the assessment calls for, and tell neighbours in advance when the drilling rig will arrive.
Sources: Camden Planning Guidance: Basements (January 2021), Camden Council: Basement developments and planning applications
Running a basement site in Swiss Cottage
Camden generally asks for a Construction Management Plan for basements, and expects one in a conservation area or beside a listed building.
Excavation is loud, and Camden keeps it to weekdays from 8am to 6pm and Saturday mornings up to 1pm unless authorised.
Fitzjohn's Avenue is heavy with traffic for Hampstead village, so spoil lorries there are timed outside the busiest periods.
Sources: Camden Local Plan 2017, Camden Planning Guidance: Basements (January 2021), Camden Council: noisy building works, Camden: Fitzjohns/Netherhall Conservation Area Character Appraisal and Management Plan (December 2022)
A basement we have built on Fitzjohns Avenue
Questions about Swiss Cottage basements
Can a Swiss Cottage basement run under the garden?
Partly: Policy A5 keeps it under half of each garden and below 1.5 times the house's footprint.
Is planning permission always needed for a basement in Camden?
Yes. Camden withdrew permitted development for basements in 2017.
Could I go down two levels?
No. Policy A5 allows a single storey, which Camden takes as about 3 to 4 metres of excavation.
Will a lightwell at the front be accepted?
Seldom: Camden resists lightwells that consume a shallow front garden, and in the Elsworthy area basements facing the road.
Who writes a Camden Basement Impact Assessment?
A chartered engineer or chartered geologist belonging to the relevant professional body.
How is possible damage next door measured?
On the Burland Scale, where the assessment must show category 1, very slight, or better.
Sources: Camden Local Plan 2017, Camden Planning Guidance: Basements (January 2021), Camden: Elsworthy Road Conservation Area Appraisal and Management Strategy (adopted 14 July 2009), Camden Council: Basement developments and planning applications
Related pages
Sources
- Camden: Fitzjohns/Netherhall Conservation Area Character Appraisal and Management Plan (December 2022)
- Camden Local Plan 2017
- Camden Planning Guidance: Basements (January 2021)
- Camden: Elsworthy Road Conservation Area Appraisal and Management Strategy (adopted 14 July 2009)
- Camden: Belsize Conservation Area Statement (agreed 20 November 2002)
- Camden: Belsize Conservation Area Statement (agreed 20 November 2002)
- Camden Council: Basement developments and planning applications
- Camden Council: noisy building works
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Background on the streets, buildings and conservation history of Swiss Cottage: Why Is It Called Swiss Cottage?