House
extensions
in Muswell Hill, N10
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Hampstead Chartered Surveyors & Building ConsultancyMuswell Hill's terraces sit on long plots with narrow frontages, many on sloping ground, so an extension here is shaped by the garden behind and the backs that neighbouring streets can see.
Haringey's appraisal foresees owners wanting to extend at the back and into the roof, and urges care wherever rear walls are visible across gardens from other streets.
We measure the garden, the back wall and the neighbours' windows first, and then draw the smallest addition that gives the family the room it needs.
Source: Haringey Council: Muswell Hill Conservation Area Character Appraisal (Conservation Area No. 3, adopted 11 February 2008)
Long plots and narrow frontages
Between Colney Hatch Lane and The Avenue, the streets form a grid of fairly wide roads lined with family terraces and linked semis on long, narrow plots.
A long, narrow garden suits a modest rear or side-return addition that leaves most of the plot as garden.
We set out the extension against the back additions of the houses either side, so that it sits in the same rhythm.
Source: Haringey Council: Muswell Hill Conservation Area Character Appraisal (Conservation Area No. 3, adopted 11 February 2008)
What Haringey's Policy DM12 expects
Policy DM12 asks extensions to respect the form, period and details of the original house, down to its chimneys and porches.
Haringey wants them subordinate to the house and respectful of the block or terrace they join.
Its supporting text says a rear extension across the full width of the house is not normally acceptable, and that one should sit lower than the ridge and be no deeper than keeps neighbours free of overlooking and lost light.
Source: Haringey Council: Development Management DPD (Haringey Local Plan, adopted July 2017)
Which extensions need permission in a conservation area
In a Haringey conservation area a house needs permission for a single-storey rear extension beyond 3 metres, or 4 metres if detached, for any rear extension of more than one storey and for any side extension.
Off designated land, a single-storey rear extension of over 3 and up to 6 metres on most houses can use the prior approval route instead.
In that process the council consults the adjoining neighbours and decides whether the effect on them is acceptable.
Measurements run from the original house: the house as first built, or as it stood on 1 July 1948, so a previous owner's addition already counts.
Sources: Haringey Council: Works that need planning permission (conservation areas), Planning Portal: Extensions, Prior approval
Side extensions and the gaps between pairs
On Queens Avenue the paired houses have wide frontages separated by small gaps that define their form in the street.
On Kings Avenue the gaps between the houses keep the pattern of the street regular.
The appraisal calls the substantial side extension at No 2 Queens Avenue over-dominant in the street.
Where a side addition is wanted, we set it well back from the front and keep it low, so that the gap still reads from the pavement.
Source: Haringey Council: Muswell Hill Conservation Area Character Appraisal (Conservation Area No. 3, adopted 11 February 2008)
Backs that can be seen from the street
From Dukes Avenue the backs of houses on Elms Avenue and Methuen Park are on open view, and two Methuen Park houses carry bulky three storey rear extensions with mansards.
At No 40 Hillfield Park a large two storey rear extension turns the corner and is plain to see from St James's Lane.
For a corner house or a plot with an open back, we add the view from the road to our drawings and design the extension to be looked at.
Source: Haringey Council: Muswell Hill Conservation Area Character Appraisal (Conservation Area No. 3, adopted 11 February 2008)
Extending on a sloping garden
In the Collins streets off Grand Avenue the land falls southwards, and the houses climb the slope in steps.
On Dukes Avenue much of the housing sits raised above the street, and the gardens behind follow that level.
A falling garden can give a lower kitchen floor with steps up to the lawn, or a level link with a retaining wall; we draw both before choosing.
Source: Haringey Council: Muswell Hill Conservation Area Character Appraisal (Conservation Area No. 3, adopted 11 February 2008)
Foundations in Muswell Hill clay
Haringey's history of the area describes heavy clay at the rim of a plateau, once threaded with streams that kept builders away.
Clay soils swell and shrink with moisture, so foundations need to go deeper, and nearby trees can push them deeper still.
Next to an existing footing, good practice is to dig at least to its depth, in short sections so it is not undermined.
Sources: Haringey Council: Muswell Hill Conservation Area Character Appraisal (Conservation Area No. 3, adopted 11 February 2008), Planning Portal: Extensions, Building Regulations: Foundations
Drains and sewers behind the house
Building within 3 metres of an existing drain or sewer brings in the building-over-sewers provisions of Approved Document H.
Building over a sewer deeper than 3 metres or wider than 225mm needs the sewerage undertaker's permission.
Haringey's plan lists Muswell Hill among the places where sewers have flooded.
We find the drain runs with a camera survey before the design is fixed, so the footprint does not have to move later.
Sources: GOV.UK: Approved Document H, Drainage and waste disposal (2015 edition), Haringey Council: Development Management DPD (Haringey Local Plan, adopted July 2017)
Garden trees
Haringey asks for six weeks' warning before work to a conservation-area tree with no preservation order, once its trunk measures 7.5cm or more at 1.5 metres above the ground.
Working on such a tree without consent is an offence, and a protected tree needs an application.
If a tree stands near the new footprint, an arboriculturist sets out its root area before we choose foundations.
Source: Haringey Council: Tree work in a conservation area
Matching red brick, tile and timber
In the Collins streets red brick is set off by red tile or slate, red-tiled porch roofs and white render and joinery, a uniformity that small changes can upset.
The appraisal puts good external materials, especially good facing brickwork, first among design considerations.
Policy DM9 asks extensions in conservation areas to complement the scale, proportions, materials and details of the house.
Sources: Haringey Council: Muswell Hill Conservation Area Character Appraisal (Conservation Area No. 3, adopted 11 February 2008), Haringey Council: Development Management DPD (Haringey Local Plan, adopted July 2017)
Building control and the neighbours
Most extensions need building regulations approval, the Planning Portal says.
A wall built on the boundary, or a trench dug close to the house next door, has to be notified to that neighbour under the Party Wall Act.
We send the party wall notices with drawings that match the planning set, so the neighbours see one scheme.
Sources: Planning Portal: Is building regulations approval needed for an extension?, GOV.UK: Party walls and building work
Muswell Hill extension questions
Do I need planning permission for a rear extension in Muswell Hill?
In a Haringey conservation area, yes for a single-storey extension beyond 3 metres (4 metres detached) and for any rear extension of more than one storey.
Can I build a side extension on my Muswell Hill semi?
It needs permission in a conservation area, and Haringey's appraisal values the gaps between paired houses.
Will Haringey accept a full-width rear extension?
Not normally; its policy expects extensions to be subordinate and below the ridge.
Why do foundations go deeper here?
Muswell Hill sits on heavy clay, and clay that swells and shrinks needs deeper footings, more so near trees.
Is building regulations approval needed?
For most extensions, yes.
Can I cut back a garden tree for the extension?
In a conservation area, give Haringey six weeks' notice first, or apply if the tree has a preservation order.
Sources: Haringey Council: Works that need planning permission (conservation areas), Haringey Council: Muswell Hill Conservation Area Character Appraisal (Conservation Area No. 3, adopted 11 February 2008), Haringey Council: Development Management DPD (Haringey Local Plan, adopted July 2017), Planning Portal: Extensions, Building Regulations: Foundations, Planning Portal: Is building regulations approval needed for an extension?, Haringey Council: Tree work in a conservation area
Related pages
Sources
- Haringey Council: Muswell Hill Conservation Area Character Appraisal (Conservation Area No. 3, adopted 11 February 2008)
- Haringey Council: Development Management DPD (Haringey Local Plan, adopted July 2017)
- Haringey Council: Works that need planning permission (conservation areas)
- Planning Portal: Extensions, Prior approval
- Planning Portal: Extensions, Building Regulations: Foundations
- GOV.UK: Approved Document H, Drainage and waste disposal (2015 edition)
- Haringey Council: Tree work in a conservation area
- Planning Portal: Is building regulations approval needed for an extension?
- GOV.UK: Party walls and building work
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