House
extensions
in Swiss Cottage, NW3

New building, garden rooms included, should not bite deeply into back gardens, the Fitzjohns/Netherhall appraisal says, and it names the gardens beside street frontages along Nutley Terrace as especially sensitive.

Nutley Terrace crosses all four parallel avenues, so for long stretches it is lined with side walls and back gardens, not front doors.

Camden lists back extensions, swimming pools, lightwells, outbuildings and over-generous paving as the ways rear garden space has been lost in that area.

Garden trees and hedges should stay, and where a tree has to go, a similar one should be planted close by; tree work there must be notified to Camden first, and many trees also have preservation orders.

Belsize's statement goes further for Eton Avenue and Fellows Road: applications should identify every tree within 10 metres of the works, underground works included.

Sources: Camden: Fitzjohns/Netherhall Conservation Area Character Appraisal and Management Plan (December 2022), Camden: Belsize Conservation Area Statement (agreed 20 November 2002), Camden: Belsize Conservation Area Statement (agreed 20 November 2002)

To the Elsworthy strategy the historic pattern of backs is integral to the place, and rear extensions that break it will not be accepted.

Near Fitzjohn's Avenue, an addition that disrupts the uniform elevations of a group is not acceptable, and side extensions or infill are resisted where a gap is closed or a building's symmetry spoiled.

The spaces between houses should remain wide enough to see the trees behind and to get round the side for maintenance.

In Belsize, rear extensions are refused where they would spoil the even back of an unspoilt terrace or group, because rear elevations are often seen from neighbouring streets.

Along King Henry's Road the houses have limited front gardens and more generous back ones, which is where any addition would have to fit.

Sources: 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), Camden: Belsize Conservation Area Statement (agreed 20 November 2002)

Inside a conservation area, cladding, side extensions and back extensions of more than one storey all fall outside permitted development under government guidance.

Flats have none of these householder rights.

Where a house does qualify, a larger single-storey rear addition goes through prior approval, measured from the house as first built, or as it stood on 1 July 1948.

If the route is unclear, a Lawful Development Certificate settles that no application is needed.

West of Finchley Road the Article 4(1) factsheet leaves the rear untouched, and points readers wanting to extend to Camden's website.

Sources: MHCLG: Permitted development rights for householders, Technical Guidance (September 2019), Planning Portal: Extensions, Prior approval, Camden: Swiss Cottage Conservation Area, what the new planning measures mean for you (Article 4(1) factsheet, 1 September 2010, updated June 2026)

Trial pits dug beside the house show the engineer what the existing footings rest on before the new foundations are drawn.

The back wall is only broken through once the steels are on site and the props are standing, and every evening a temporary screen closes the house.

We agree the garden access, the spoil route and a storage corner with the client before starting, so the lawn that will remain is fenced off from day one.