House
extensions
in Highgate, N6
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Hampstead Chartered Surveyors & Building ConsultancyA Highgate extension is judged against the house, the garden and the gaps between houses, under Camden's or Haringey's rules and the neighbourhood plan.
Under Policy DH3, a Highgate rear extension should stay secondary to the original house, follow its design and materials, spare the neighbours and leave a garden in proportion to theirs.
Our first drawings show the extension beside the neighbours' backs and gardens, because that is how the council will look at it.
Source: Highgate Neighbourhood Plan (adopted by Haringey in July 2017 and Camden in September 2017)
Rear gardens and how far to build
The plan says rear gardens contribute to Highgate's character, amenity and ecology, so extensions should not take a disproportionate share of them.
Camden's guidance similarly expects a reasonably sized garden to remain.
In Camden's appraisal, the historic pattern of rear elevations is part of the area's character, and extensions that compromise it will not be acceptable.
Sources: Highgate Neighbourhood Plan (adopted by Haringey in July 2017 and Camden in September 2017), Camden Planning Guidance: Home Improvements (January 2021), Camden: Highgate Conservation Area Appraisal and Management Strategy (adopted October 2007)
Side extensions and the gaps between houses
Policy DH4 says side extensions, including enlarged garages, should not block or largely infill the gaps between buildings, and should stay subordinate.
The plan explains why: gaps between houses, often with views of mature gardens, are a valued feature of many Highgate streets.
Camden's guidance generally expects side extensions to be single storey.
Sources: Highgate Neighbourhood Plan (adopted by Haringey in July 2017 and Camden in September 2017), Camden Planning Guidance: Home Improvements (January 2021)
Each borough's own rules
Haringey's Policy DM12 asks for high-quality residential extensions that take account of neighbours' privacy and amenity.
For daylight, Camden measures a rear extension with two angle tests, at 45 and 25 degrees, or accepts a BRE study instead, and it wants the addition to read as secondary to the house in shape, size and detail.
Where the extension has a flat top, Camden would rather see a biodiverse roof, on 100mm or more of growing medium, than a sedum mat.
Sources: Haringey: Development Management DPD (adopted July 2017), Camden Planning Guidance: Home Improvements (January 2021)
Glazing, rooflights and light spill
Camden's guidance asks that rear extensions do not cause light pollution or excessive light spill on neighbours, including flats above where a house has been divided.
Rooflights on a ground-floor extension should sit away from the building line or use obscured glass to limit that spill.
We show the glazing in the evening as well as the day on our drawings, so neighbours can see how the extension will look after dark.
Source: Camden Planning Guidance: Home Improvements (January 2021)
Permitted development in Highgate
In conservation areas, government guidance takes side extensions and rear extensions of more than one storey out of permitted development.
A flat, or a building of flats, has no householder permitted development rights.
Where a proposal may need no application, a Lawful Development Certificate gives certainty.
Source: MHCLG: Permitted development rights for householders, Technical Guidance (September 2019)
Trees near the extension
On the Camden side, work to a tree in a conservation area with a trunk wider than 75mm at 1.5 metres needs advance notice.
Clay soils swell and shrink with moisture, so foundations near trees may need to go deeper.
The neighbourhood plan stresses protecting mature trees to limit effects on the water table.
Sources: Camden Council: Conservation areas, Planning Portal: Extensions, Building Regulations: Foundations, Highgate Neighbourhood Plan (adopted by Haringey in July 2017 and Camden in September 2017)
Foundations, drains and structure
Most extensions need building regulations approval.
Building over or within 3 metres of a drain or sewer engages Approved Document H, and deeper or larger sewers should not be built over at all without agreement.
Beside a neighbour's wall, excavating at least to the bottom of their foundation is good practice.
On Highgate's slopes we also check the level change across the garden, which can mean steps or a retaining wall in the extension's cost.
Sources: Planning Portal: Is building regulations approval needed for an extension?, GOV.UK: Approved Document H, Drainage and waste disposal (2015 edition), Planning Portal: Extensions, Building Regulations: Foundations
Pre-application advice
Camden's advice service for householders has two tiers, and the lower tier handles plain cases such as one single-storey extension at the back.
For a Haringey address we prepare the same pack of drawings and photographs and ask the council for its view before a full application.
Source: Camden Council: Pre-planning application advice for homeowners
A rear extension nearby
Questions about extending a Highgate house
How big can my rear extension be?
Highgate's plan asks for it to stay subordinate and leave a garden proportionate to the neighbours'.
Can I extend to the side?
Only where it does not block or largely infill the gap between houses, under Policy DH4.
Do I have permitted development rights?
Fewer in a conservation area: side extensions and rear extensions over one storey are excluded.
Does my flat have extension rights?
No. Householder permitted development does not apply to flats.
What roof should a flat extension have?
A biodiverse green roof on a growing layer of 100mm or more is Camden's preference.
What does a house extension in Highgate cost?
Pricing: quoted after a feasibility visit.
Sources: Highgate Neighbourhood Plan (adopted by Haringey in July 2017 and Camden in September 2017), MHCLG: Permitted development rights for householders, Technical Guidance (September 2019), Camden Planning Guidance: Home Improvements (January 2021)
Sources
- Highgate Neighbourhood Plan (adopted by Haringey in July 2017 and Camden in September 2017)
- Camden Planning Guidance: Home Improvements (January 2021)
- Camden: Highgate Conservation Area Appraisal and Management Strategy (adopted October 2007)
- Haringey: Development Management DPD (adopted July 2017)
- MHCLG: Permitted development rights for householders, Technical Guidance (September 2019)
- Camden Council: Conservation areas
- Planning Portal: Extensions, Building Regulations: Foundations
- Planning Portal: Is building regulations approval needed for an extension?
- GOV.UK: Approved Document H, Drainage and waste disposal (2015 edition)
- Camden Council: Pre-planning application advice for homeowners
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