House
extensions
in Bushey, WD23
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Three things settle whether a Bushey extension can be built without an application, and how large Hertsmere will let it be when one is needed: the house type, the conservation area and the space around the house.
Pairs of semis set the pattern across much of Bushey: at the 2021 Census they housed 38.0% of households in Bushey North and 30.5% in Bushey Park, while detached houses were commonest in Bushey Heath, at 34.1%. Hertsmere's design guide names Bushey among the places where the street scene depends on open gaps between houses, and it expects those gaps to survive an extension.
Under the gardens lies clay. The borough's flood assessment describes Bushey's soils as clays of low permeability that are waterlogged for part of the year, which bears on how deep the foundations go and where rainwater from a new roof can be sent.
Sources: ONS Census 2021 TS044 accommodation type via Nomis (NM_2062_1), 2022 wards for bushey; Hertsmere Borough Council: Planning and Design Guide Part E: Guidelines for Residential Extensions and Alterations (adopted 2006)
Does a Bushey extension need an application?
Under Class A of the householder rules, a rear addition of a single storey may go ahead as permitted development: it may project beyond the original rear wall by up to 4 metres where the house is detached, 3 metres where it is not, and may be no taller than 4 metres. Within 2 metres of a boundary its eaves are capped at 3 metres, outbuildings and extensions together may not cover more than half the curtilage outside the original house, and the materials must look like the existing ones.
Bushey's four conservation areas count as article 2(3) land, where the rules close two doors: nothing built out beyond the original house's side walls, nor any rear addition taller than one storey, unless permission is granted. Hertsmere's conservation page singles out side extensions as one of the extra restrictions.
An Article 4 direction can take the remaining rights away. The direction on the Reveley Almshouses withdraws the building of extensions and porches, and the two directions on the Warren Estate roads in Bushey Heath, each worded differently, are read for the exact property before anything is drawn.
Bushey, in the High Street appraisal's words, stands within an area of greenbelt. For a house inside the Green Belt itself, Policy SADM26 asks whether an extension, alone or together with earlier ones, is disproportionate to the original building; our Hertsmere page sets out the test.
Sources: legislation.gov.uk: GPDO 2015 (SI 2015/596), Schedule 2 Part 1, development within the curtilage of a dwellinghouse (latest available revised); legislation.gov.uk: Town and Country Planning (General Permitted Development) (England) Order 2015 (SI 2015/596), article 2 (latest available revised); legislation.gov.uk: GPDO 2015 (SI 2015/596), Schedule 1 Part 1, Article 2(3) land (latest available revised); Hertsmere Borough Council: Conservation areas in Hertsmere; Hertsmere Borough Council: Site Allocations and Development Management Policies Plan (adopted November 2016); Hertsmere Borough Council (BEAMS Ltd): Bushey High Street Conservation Area Appraisal 2008, main report; Hertsmere Borough Council: Article 4 Directions - Conservation
What Hertsmere's design guide asks of a Bushey extension
Part E of the council's Planning and Design Guide, adopted in 2006 as a supplementary planning document, is used whenever Hertsmere assesses an application. Its first test is the 45-degree line: an extension should stay comfortably inside a 45-degree line projected from the nearest edge of a neighbour's front or rear windows, counting only habitable rooms and kitchens.
On single-storey work the guide is relaxed about flat roofs at the back, unless a pitched or hipped roof would suit the house and street better, and limits height to 3 metres with a flat roof or 4 metres with a pitched one. Any side windows should be high level and non-opening or obscure glazed, and the house should keep most of its garden.
Where spacing defines the street, as the guide says it does in parts of Bushey, the gap must be kept: a two-storey side extension keeps a gap of at least 2 metres to the side boundary and sits 1 metre or more behind the main front wall. More bedrooms can mean more parking, and losing healthy trees or hedges that add to the area will count against a scheme.
At Farm Way, the former Ministry of Defence housing south-west of Bushey Heath, Policy SADM31 adds its own tests. Additions must not dominate or overbear the house's original proportions, new work should match the existing buildings in height, bulk, roof design, front projections and ridge and eaves heights, and the soft landscaping in front should stay.
Sources: Hertsmere Borough Council: Planning and Design Guide SPD; Hertsmere Borough Council: Planning and Design Guide Part E: Guidelines for Residential Extensions and Alterations (adopted 2006); Hertsmere Borough Council: Draft Planning and Design Guide SPD Part D (draft for DM use and public consultation, October 2016); Hertsmere Borough Council: Site Allocations and Development Management Policies Plan (adopted November 2016)
Clay, brooks and the Colne under a Bushey extension
The 2023 flood assessment finds Bushey's soils to be clays of low permeability, seasonally waterlogged and producing medium to high runoff, and the High Street appraisal records sand, gravels and clays beneath the old village. On clay a soakaway may barely drain, and nearby trees affect how deep foundations go, so the ground is tested before anything is sized.
Watercourses run through the town. The Hilfield Brook crosses North Bushey from east to west, the Environment Agency's warning area for the River Colne at Watford is described as including Bushey, and residents have reported flooding around Little Bushey Lane and Finch Lane. Work within 9m of any watercourse needs the borough's prior consent, and anything that could affect the flow of an ordinary watercourse needs consent from Hertfordshire County Council as the lead local flood authority.
The Environment Agency says that householders planning a straightforward, low-risk extension may be able to get the flood risk information from its Flood Map for Planning on their own. We run that check for the address and add a flood risk assessment to the application where it is needed.
Before any work on or right at the boundary line, or any digging below the neighbour's foundation level close to their house, the neighbour must be told. They have no power to block lawful building, though they can influence the way it is done and its timing, and silence after a notice does not count as agreement.
Sources: Hertsmere Borough Council / AECOM: Level 1 Strategic Flood Risk Assessment (2023); Hertsmere Borough Council (BEAMS Ltd): Bushey High Street Conservation Area Appraisal 2008, main report; Environment Agency flood-monitoring API: flood warning area 062FWF28Watford; Environment Agency (GOV.UK service): Get flood risk information for planning in England (Flood map for planning); GOV.UK: Party walls and building work (printable guide); GOV.UK: Party walls and building work - work you must tell your neighbour about
From survey to sign-off on a Bushey extension
Our London team takes on extensions in Bushey: in-house architects and designers draw the scheme, our structural engineers design the foundations and steels, and we work with Hampstead Chartered Surveyors & Building Consultancy. Planning goes to Hertsmere Borough Council, and the building regulations, which cover the extension of buildings, go to Hertfordshire Building Control or a private registered building control approver.
Trial holes dug beside the house show us the existing footings and the clay before the engineer designs, and the drainage runs and any soakaway are placed from what the holes reveal.
On site the new foundations and structure go in before the existing back wall is opened, so the house stays closed to the weather until the new frame can carry the roof.
Outside Bushey, and in London rather than Hertfordshire: Project example: Hampstead Garden Suburb, NW11. That project of ours added a rear extension of a single storey to an Arts and Crafts house, and had to win consent from both the Hampstead Garden Suburb Trust and the council, as its case study records.
Sources: GOV.UK: Building regulations approval - when you need approval; Hertsmere Borough Council: Hertfordshire Building Control Limited; GOV.UK: Building regulations approval (printable guide); Hampstead Renovations: Meadway, NW11 case study
House Extensions in Bushey: Questions
Can I build a rear extension in Bushey under permitted development?
Often, if the house is outside a conservation area and free of any Article 4 direction. Depth is the main limit for a one-storey rear extension: on a detached house it may run 4 metres out from the original rear wall, on others 3 metres. It must also stay at or under 4 metres high, with eaves no higher than 3 metres within 2 metres of a boundary. Earlier extensions joined to it count towards the limits, so we check what has been built before.
Does an extension in one of Bushey's conservation areas need planning permission?
Yes for a side extension, and yes for a rear extension rising above one storey: the householder rules treat conservation areas as article 2(3) land and allow neither there. A single-storey rear extension may still be permitted development, except where an Article 4 direction removes that right, as the Reveley Almshouses direction does. Hertsmere does not normally accept outline applications in conservation areas, so the application goes in with full drawings.
Where does flood risk come into a Bushey extension?
It starts with location. The Environment Agency's warning area for the River Colne at Watford is described as including Bushey, the Hilfield Brook runs through North Bushey, and the council's records put Bushey among the localities most often affected by flooding. On simple house extensions, the Environment Agency notes that owners may be able to fetch the flood information from its Flood Map for Planning without help, and work within 9m of a watercourse needs the borough's consent.
Who signs off building regulations for an extension in Bushey?
Hertfordshire Building Control, or a private registered building control approver. The Building Regulations 2010 cover the extension of buildings, so an extension needs approval even when planning permission is not required, and the certificates matter when the house is sold.
Does the Farm Way character area in Bushey Heath limit extensions?
Policy SADM31 covers the former Ministry of Defence housing there. The council counts the absence of extensions to the original houses among the reasons the area is distinctive, and it permits new work that complements their height, bulk and roof design without dominating the original proportions. The area is less tightly restricted than a conservation area, and we design additions there to stay subordinate to the house.
What should I have ready when you visit about a Bushey extension?
Have the deeds plan, any past planning permissions and drawings to hand, and tell us about earlier extensions or conservatories, since those count towards the permitted development limits. Clear a way to the back of the house so we can see the rear wall, the drains and the boundary, and point out any large trees near where the extension would go.
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