House
extensions
in Hampstead Garden Suburb, NW11
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Hampstead Chartered Surveyors & Building ConsultancyGarden-room, kitchen and family-room extensions for Suburb houses, drawn to the rear-elevation, roofline and group tests the Trust and Barnet apply, with trees, hedges and neighbours mapped before the first sketch.
The joint guidance begins its extension advice plainly: an extension permanently alters a house, some extension can often be allowed without harm, and in some cases it may not be possible to extend at all.
Our first question on any Suburb extension is therefore how much the house has already grown, and what the original architect meant it to look like from the garden.
Source: Hampstead Garden Suburb Trust and Barnet Council: Conservation Area Design Guidance (2010)
The Tests Barnet and the Trust Apply
Extensions that stay inside an imaginary line continuing the main roof slopes down to the ground are preferred, and every previous extension is taken into account.
A rear extension should generally be no wider than half the width of the rear elevation, and in most cases less; front extensions are unlikely to be acceptable.
Extensions that intrude on well-established views or the space between houses, such as two-storey side extensions or rooms above garages, are not normally approved.
New windows to habitable rooms that significantly increase overlooking will not normally be acceptable.
Source: Hampstead Garden Suburb Trust and Barnet Council: Conservation Area Design Guidance (2010)
Houses Designed as Groups
Many Suburb houses were composed as groups around greens and closes. The guidance warns that altering one house can destroy the balance of the whole, and that such changes are likely to be refused if they harm the group.
Unwin designed the backs of houses as carefully as the fronts, and they can often be seen from footpaths and allotments, so lower standards of design are not acceptable at the rear.
Even the smallest cottages were designed with the same care as the larger houses.
We photograph the house within its group, from the street and from any public path behind, before sketching an extension.
Source: Hampstead Garden Suburb Trust and Barnet Council: Conservation Area Design Guidance (2010)
Conservatories, Sun Rooms and the Garden Around Them
Conservatories are generally considered harmful to the Suburb's character and will not normally be approved; a glazed sun room with a tiled or lead roof may be possible on some houses.
The garden is controlled too. More paving, retaining walls, steps or changed levels need Trust consent, and boundary hedges and trees must not be removed without it.
Decking is not characteristic of the Suburb and will not generally be approved.
Sources: Hampstead Garden Suburb Trust and Barnet Council: Conservation Area Design Guidance (2010), Hampstead Garden Suburb Trust: Planning FAQs
Trees, Hedges and Foundations
Plans must show the species, size and position of trees and significant planting, and applicants should take account of British Standard BS5837.
The guidance advises employing an architect and, where appropriate, an arboricultural consultant, and keeping the architect on to supervise the work on site.
Tree work needs the Trust's written consent and Barnet's approval, and hedges cannot be removed or replaced without the Trust's written consent.
The Planning Portal notes that clay soils can need deeper foundations, and trees on clay can push them deeper than first expected.
Sources: Hampstead Garden Suburb Trust and Barnet Council: Conservation Area Design Guidance (2010), Hampstead Garden Suburb Trust: Works to Trees and Hedges on the Suburb, Planning Portal: Extensions, Building Regulations: Foundations
What a Trust Extension Application Contains
The Trust asks for full plans and elevations at 1:100 or 1:50 showing the neighbouring houses, sections through the extension, and engineer's drawings for major structural work.
Its staff will discuss a scheme before you apply, free of charge, though they can only indicate what may be acceptable; the decision rests with the Trust Council after its Property and Plans Committee.
The programme depends on the agreed scope, approvals, site conditions and procurement. Discuss the sequence of work at a feasibility visit.
Sources: Hampstead Garden Suburb Trust and Barnet Council: Conservation Area Design Guidance (2010), Hampstead Garden Suburb Trust: Planning FAQs
Building Regulations for the New Rooms
The Planning Portal says most extensions need building regulations approval.
Opening the back wall into the extension means carrying the masonry above on new beams, usually two, each with proper bearings at either end, and the Planning Portal says a steel beam normally needs fire protection.
Building regulations approval from Barnet is needed for structural alterations and additions.
Sources: Planning Portal: Is building regulations approval needed for an extension?, Planning Portal: Extensions, Building Regulations: Structural Opening, Hampstead Garden Suburb Trust and Barnet Council: Conservation Area Design Guidance (2010)
Extensions in and near the Suburb
Questions about extending a Suburb house
How wide can a rear extension be?
The joint guidance says it should generally be no wider than half the width of the rear elevation, and in most cases less.
Can I build a two-storey side extension?
Normally not. The Trust and Barnet do not normally approve extensions that intrude on the space between houses, such as two-storey side extensions or rooms above garages.
Will Trust staff decide my extension application?
Usually not. Staff can decide replacement windows and doors, like-for-like sheds, pipework and other minor changes under delegated powers; applications are otherwise considered first by the Property and Plans Committee and decided by the Trust Council.
Do my neighbours have a say?
Yes.
Is a conservatory possible?
Not normally. The guidance says conservatories will not normally be approved, although a glazed sun room with a tiled or lead roof may be possible on some houses.
Sources: Hampstead Garden Suburb Trust and Barnet Council: Conservation Area Design Guidance (2010), Hampstead Garden Suburb Trust: Planning FAQs
Sources
- Hampstead Garden Suburb Trust and Barnet Council: Conservation Area Design Guidance (2010)
- Hampstead Garden Suburb Trust: Planning FAQs
- Hampstead Garden Suburb Trust: Works to Trees and Hedges on the Suburb
- Planning Portal: Extensions, Building Regulations: Foundations
- Planning Portal: Is building regulations approval needed for an extension?
- Planning Portal: Extensions, Building Regulations: Structural Opening
Guides & Local Reading
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