House
extensions
in Dartmouth Park, NW5
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Hampstead Chartered Surveyors & Building ConsultancyBehind Dartmouth Park's villas the backs are seen from the next road and through the gaps between pairs, so an extension here is designed for those views.
The neighbourhood plan sees a rear extension as a low-impact way of giving a growing family room, provided it does not eat disproportionately into the garden.
We start an extension from the garden end: what has to stay, which trees are close, and how the back of the house is seen from the street behind.
Source: Dartmouth Park Neighbourhood Plan (made by Camden, 2 March 2020)
What Policy DC4 asks of an extension
Policy DC4 backs small extensions at the side, rear or roof that are subordinate to the original house and match its design, proportions, materials and detail, without harming the neighbours' privacy, outlook or light or the street scene.
For a rear extension it adds that the garden should not lose an excessive share, nor the green space that gives the area its character.
Every plan we submit shows the remaining garden as a measured area, so that test can be judged straight from the drawings.
Source: Dartmouth Park Neighbourhood Plan (made by Camden, 2 March 2020)
The historic backs
Camden's appraisal notes many interesting historic rear elevations here, a good number of them in public view from surrounding streets.
It will not accept rear extensions that depart significantly from the original pattern of backs in a street or group.
Behind Boscastle Road, for instance, Nos 8 to 24 show uniform three-storey closet wings, and Crockett's houses on Laurier Road have three-storey rear extensions finished with a curved parapet.
Our survey photographs the backs of the whole group, so the new room is designed to sit inside a pattern rather than against it.
Source: Camden: Dartmouth Park Conservation Area Appraisal and Management Statement (adopted 22 January 2009)
Gaps between the houses
Camden will resist building in the gaps between semi-detached and detached houses, beside road junctions, at the ends of terraces and where a corner garden runs along a side road.
Policy DC4 says the same of side extensions to detached and semi-detached houses where the gap adds to local character.
In Dartmouth West those gaps reveal shrubs and trees, and York Rise offers long views over the back gardens.
Where a side addition is proposed on a villa, we keep it low and well back so the gap still reads from the pavement.
Sources: Camden: Dartmouth Park Conservation Area Appraisal and Management Statement (adopted 22 January 2009), Dartmouth Park Neighbourhood Plan (made by Camden, 2 March 2020)
End-of-terrace houses
The neighbourhood plan allows that a site may exceptionally justify an extension that is not subordinate, giving the example of an end-of-terrace house extended in the style of the original.
If a client's house ends a group, we test both routes: a modest addition, and a continuation of the terrace's own design.
Source: Dartmouth Park Neighbourhood Plan (made by Camden, 2 March 2020)
Garden rooms and backland
Under Policy DC4, building in a back garden is limited to uses that serve the house, such as sheds, conservatories and greenhouses, that do not take an excessive part of it.
The appraisal lists unsympathetic rear and side extensions, inappropriate roof terraces and building on large green backland plots among the area's problems.
A garden room for study or work is drawn as part of the house's use, not as a separate home, and placed to keep the garden's trees.
Sources: Dartmouth Park Neighbourhood Plan (made by Camden, 2 March 2020), Camden: Dartmouth Park Conservation Area Appraisal and Management Statement (adopted 22 January 2009)
Trees, hedges and root zones
Hedges and trees in private gardens give the area its semi-rural feel, and gardens that can be seen open long views between groups of houses.
Where trees stand on or next to a site, street trees included, an arboricultural report must go with the application, explaining how they will be protected and justifying any felling.
Policy ES2 of the neighbourhood plan asks for significant trees to be kept and cared for during the work in line with BS5837:2012.
An arboriculturist joins us before the foundation design, so footings are drawn around the roots rather than through them.
Sources: Camden: Dartmouth Park Conservation Area Appraisal and Management Statement (adopted 22 January 2009), Dartmouth Park Neighbourhood Plan (made by Camden, 2 March 2020)
Grain, plot width and materials
Policy DC3 asks new work to respect the street's orientation, grain, set-backs, front gardens and walls, and its plot widths.
It also wants extensions subordinate and in keeping with adjoining houses, in materials that complement those nearby.
On a stock brick villa that means matched or reclaimed brick with timber joinery, or a light structure that is plainly new and sits below the closet wing.
Source: Dartmouth Park Neighbourhood Plan (made by Camden, 2 March 2020)
Permitted development and Article 4
In a conservation area, government guidance takes side extensions, cladding and rear additions of more than one storey out of permitted development.
Camden's 2009 strategy saw a need for Article 4 directions here; the only one it records was made in 1980 to keep a painted sign at 33 York Rise.
A Lawful Development Certificate gives certainty that a scheme needs no application.
Sources: MHCLG: Permitted development rights for householders, Technical Guidance (September 2019), Camden: Dartmouth Park Conservation Area Appraisal and Management Statement (adopted 22 January 2009)
Building on a slope
The land drops some 35 metres across the area, and smaller valleys run across that fall.
On Dartmouth Park Avenue most villas have a basement that the slope turns into a garden floor.
Where the garden sits below the ground floor, the extension can open from the lower level, with steps or a terrace taking up the change in height.
Source: Camden: Dartmouth Park Conservation Area Appraisal and Management Statement (adopted 22 January 2009)
Light for the neighbours
Camden tests neighbours' daylight with its 45-degree and 25-degree rules, or with a BRE study instead.
A rear extension should not throw excessive light at neighbours after dark, including flats above in a divided house.
We model the neighbour's nearest window and garden before fixing the height of the new roof.
Source: Camden Planning Guidance: Home Improvements (January 2021)
Ground, drains and the old stream
A culverted tributary of the Fleet follows the line of Brookfield Park, York Rise and Burghley Road.
On clay that swells and shrinks, footings must go deeper, and deeper again near trees.
Building within 3 metres of the centreline of a sewer brings in Approved Document H.
A drainage survey and trial pits come before the structural design, never after it.
Sources: Camden: Dartmouth Park Conservation Area Appraisal and Management Statement (adopted 22 January 2009), Planning Portal: Extensions, Building Regulations: Foundations, GOV.UK: Approved Document H, Drainage and waste disposal (2015 edition)
Walls, pipes and a heat pump
Camden's 2012 guidance says external wall insulation is likely to be acceptable on rears that are not highly visible, and where long views run along the backs, usually at garden level only.
New rainwater goods should be black painted metal.
A heat pump is best freestanding in the rear garden, and an application for one needs a noise impact statement.
Source: Camden: Energy efficiency planning guidance for Dartmouth Park Conservation Area (adopted 23 August 2012)
Questions about extending a Dartmouth Park house
How big can my rear extension be?
There is no fixed size: the neighbourhood plan asks that it stays subordinate and does not take an excessive part of the garden.
Can I fill the gap beside my semi-detached house?
Camden will resist building in the gaps between pairs and at the ends of terraces.
Do I need planning permission for a side extension?
Yes, in a conservation area side extensions and rear additions of more than one storey fall outside permitted development.
Will Camden want a tree report?
Yes, wherever trees stand on or next to the site, street trees included.
Can I build a studio in the garden?
Policy DC4 accepts garden buildings tied to the house's domestic use, such as sheds and greenhouses, if they do not take an excessive part of the garden.
Can an end-of-terrace house be extended in the original style?
Exceptionally yes, the neighbourhood plan says, even where the result is not subordinate.
Sources: Dartmouth Park Neighbourhood Plan (made by Camden, 2 March 2020), Camden: Dartmouth Park Conservation Area Appraisal and Management Statement (adopted 22 January 2009), MHCLG: Permitted development rights for householders, Technical Guidance (September 2019)
Related pages
Sources
- Dartmouth Park Neighbourhood Plan (made by Camden, 2 March 2020)
- Camden: Dartmouth Park Conservation Area Appraisal and Management Statement (adopted 22 January 2009)
- MHCLG: Permitted development rights for householders, Technical Guidance (September 2019)
- Camden Planning Guidance: Home Improvements (January 2021)
- Planning Portal: Extensions, Building Regulations: Foundations
- GOV.UK: Approved Document H, Drainage and waste disposal (2015 edition)
- Camden: Energy efficiency planning guidance for Dartmouth Park Conservation Area (adopted 23 August 2012)
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