House Extensions in South Hampstead, NW6
Behind South Hampstead's terraces lie long gardens and shared green spaces that whole streets overlook, so an extension here is judged from the back as much as from the road.
Camden notes that only a handful of South Hampstead back elevations show from the street, while far more are seen from the private open spaces and from the backs of neighbouring houses.
Our extension drawings therefore start at the garden end: what the neighbours look at, where the trees stand and how much lawn will be left.
Source: Camden: South Hampstead Conservation Area Character Appraisal and Management Strategy (February 2011)
Rear gardens and the communal greens behind them
For the appraisal, the long and unbuilt back gardens and the private open spaces sit at the heart of the conservation area, and protecting them comes first.
It lists them by name: Broadhurst Gardens Meadow; the Maryon Wilson Green Triangle, reached from the backs of Fairhazel Gardens and Goldhurst Terrace; and three enclosed lawns, one between Canfield and Greencroft Gardens, one between Compayne and Canfield, and one between Fairhazel and Compayne.
Camden values these gardens, with the green front gardens, as wildlife corridors that also help to reduce flood risk.
Its tree survey describes continuous bands of trees across the back gardens and only intermittent cover at the front.
Source: Camden: South Hampstead Conservation Area Character Appraisal and Management Strategy (February 2011)
How much garden an extension can take
Camden reports a large number of applications here for big rear extensions and paved gardens, resists schemes that ignore the garden setting, and asks owners to keep as much planting as they can.
Building that eats into private open space is not likely to be approved, and an addition in a back garden has to leave the greater part of it as it is.
Borough-wide, Camden asks for a rear addition that stays secondary to the house in where it sits, its footprint, scale and detailing, and that leaves a garden of reasonable size.
At the first garden visit we plot a few alternative footprints on the survey and measure the open ground each would leave, and only one goes forward.
Sources: Camden: South Hampstead Conservation Area Character Appraisal and Management Strategy (February 2011), Camden Planning Guidance: Home Improvements (January 2021)
Corner plots and gardens beside the communal spaces
Gardens on corner sites or next to the communal amenity spaces get particular care, because an extension there is easier to see.
Many houses east of Fairhazel Gardens back directly onto those spaces, and there and on Compayne Gardens some upper floors have very large windows that may once have lit studios.
Rear alterations should follow the historic pattern of development and keep each house's historic features.
Towards the eastern end of Broadhurst Gardens, terraces were laid out to pass for pairs, a slim gap between neighbours concealing that the houses meet at the rear.
We mark gaps, back bays and original openings on the survey drawing, so the new work is shaped around them from the start.
Source: Camden: South Hampstead Conservation Area Character Appraisal and Management Strategy (February 2011)
Gaps between houses and side infill
In the central wedge of Aberdare, Broadhurst, Canfield, Compayne and Greencroft Gardens, the appraisal counts the gaps between houses as part of the character.
Seeing mature trees between buildings from the road gives these streets their open feel and hints at the long gardens behind.
Camden's home improvements guidance generally keeps a side extension to a single storey, though a taller one is possible in some cases.
Where a side passage is the only route to the garden, we keep bin and bicycle access in the design rather than filling it.
Sources: Camden: South Hampstead Conservation Area Character Appraisal and Management Strategy (February 2011), Camden Planning Guidance: Home Improvements (January 2021)
Planning permission and permitted development
Inside a conservation area, government guidance takes cladding, side extensions and rear extensions of more than one storey out of permitted development.
Flats have no householder permitted development rights at all, which counts for a lot in South Hampstead, where most homes, around 70% by Camden's survey, are flats.
Where a house qualifies, a larger single-storey rear extension uses the prior approval process, measured from the house as first built or as it stood on 1 July 1948.
A Lawful Development Certificate can confirm that a proposal needs no application.
Sources: MHCLG: Permitted development rights for householders, Technical Guidance (September 2019), Camden: South Hampstead Conservation Area Character Appraisal and Management Strategy (February 2011), Planning Portal: Extensions, Prior approval
Daylight, light spill and the flats upstairs
Camden expects a rear extension to pass the 45 degree and 25 degree tests in its amenity guidance, or to show compliance with BRE daylight guidance.
It also wants no excessive light spill onto neighbours, including people living above in a divided house, and asks for rooflights set back from the building line or obscured.
For the flat roof, Camden's guidance prefers a biodiverse green roof on a 100mm substrate to a sedum mat.
In a converted house we show the upstairs owners where the rooflights will sit before the application is lodged.
Source: Camden Planning Guidance: Home Improvements (January 2021)
Footings, drains and trees
Because clay moves as its moisture changes, footings are taken deeper, and trees nearby can push them much deeper than first planned.
Beside a neighbour's footing the dig goes at least to its depth in short sections, and excavating close to their foundations needs a party wall notice.
A recorded sewer within 3m of the new walls brings Approved Document H's building-over provisions into play.
Felling or cutting back a garden tree thicker than 75mm needs six weeks' notice to Camden first.
Sources: Planning Portal: Extensions, Building Regulations: Foundations, GOV.UK: Party walls and building work, GOV.UK: Approved Document H, Drainage and waste disposal (2015 edition), Camden: South Hampstead Conservation Area Character Appraisal and Management Strategy (February 2011)
From garden survey to a closed-in extension
Trial pits dug against the back wall show our engineer what the old footings rest on, and the new foundation design follows from what they reveal.
The rear wall is opened only when the steel and props are on site, and a temporary screen seals the house each evening.
Before work starts we fence off the part of the garden that will stay, agree a route for spoil and set aside a corner for materials.
Questions about extending a South Hampstead house
How far into a South Hampstead garden can an extension go?
There is no fixed depth; Camden asks that most of the garden is kept and the garden setting respected.
Will Camden judge my extension from the communal garden?
Yes. Many rear elevations are seen from the private open spaces, and gardens next to them get particular care.
Could I add two storeys at the back without applying?
No. Anything over one storey at the rear of a house in a conservation area needs planning permission.
May a garden-floor flat be extended?
With an application only, as flats carry no householder rights; check too whether your lease needs the landlord to agree.
Must Camden hear about a garden tree before it is cut?
Usually, yes. GOV.UK says that for trees in a conservation area you must notify the council 6 weeks before carrying out certain work, unless an exception applies, and much of South Hampstead is a conservation area. One exception is a tree whose diameter does not exceed 75 millimetres, measured over the bark at 1.5 metres above ground. An extension's footings can also reach roots well beyond the trunk, so it is worth raising early with Camden.
How will the neighbours' daylight be tested?
By Camden's 45 and 25 degree rules, or a BRE daylight assessment.
Sources: Camden: South Hampstead Conservation Area Character Appraisal and Management Strategy (February 2011), MHCLG: Permitted development rights for householders, Technical Guidance (September 2019), LEASE: alterations and home improvements, Camden Planning Guidance: Home Improvements (January 2021)
Sources
- Camden: South Hampstead Conservation Area Character Appraisal and Management Strategy (February 2011)
- Camden Planning Guidance: Home Improvements (January 2021)
- MHCLG: Permitted development rights for householders, Technical Guidance (September 2019)
- Planning Portal: Extensions, Prior approval
- Planning Portal: Extensions, Building Regulations: Foundations
- GOV.UK: Party walls and building work
- GOV.UK: Approved Document H, Drainage and waste disposal (2015 edition)
- LEASE: alterations and home improvements
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