House
extensions
in Gerrards Cross, SL9
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Many Gerrards Cross houses were first extended in the 1920s, by architects still at home in the Arts and Crafts idiom. A new addition is judged against that work, and against the plots, gaps and trees the local plans protect.
Approved building plans show the appraisal's authors that many garden-village houses were extended long ago, often in the 1920s, when architects still knew the Arts and Crafts language and made their additions sympathetic to the Edwardian originals. Where houses have since been extended or given garages, the gaps between them have narrowed, though they are generally still wider than average.
Detached houses held 1,950 of the ward's 3,408 households at the 2021 Census, so the typical extension here is added to a house standing on its own plot. Spacing, roof form, trees and the street therefore shape the design more than any shared rear wall.
Sources: South Bucks District Council: Gerrards Cross Common and Centenary Conservation Areas Character Appraisal (April 2009); ONS/Nomis: Census 2021 TS044 Accommodation type, 2022 ward Gerrards Cross (E05013145)
Saved policy H11 and the house extensions guide
Where planning permission is needed, saved policy H11 of the 1999 Local Plan is the test, and the neighbourhood plan lists it among the policies it relies on. An addition has to be integral to the dwelling and harmonise with it in form, height, scale and design, without harming neighbours through overlooking, overdominance, obtrusiveness or lost daylight.
Two of its rules decide the shape of most schemes. Any extension above one storey, or reaching first-floor level, keeps a gap of one metre or more to each flank boundary; and the council's practice is to require extensions to pitched-roof houses to be pitch-roofed themselves, to match.
The plan's Appendix 8 guide fills in the detail. An extension should normally be indistinguishable from the original dwelling, with roof tiles and facing bricks of the same size, colour and design and windows aligned with the existing ones; where an exact match cannot be found, the front wall is better set back to give a visual break. Single-storey projections stay within a 60° line from the middle of a neighbour's nearest habitable-room window, first-floor and two-storey ones within 45°.
The guide applies the same principles to conservatories, and it treats flat roofs on two-storey extensions as usually unacceptable.
Sources: South Bucks District Council: South Bucks District Local Plan, adopted March 1999, consolidated September 2007 and February 2011; Gerrards Cross Town Council / Buckinghamshire Council: Gerrards Cross Neighbourhood Plan 2017-2040, Made Plan (December 2025)
Extending in the conservation areas and areas of exceptional character
Both conservation areas fall within article 2(3) land, where the householder right to extend is narrower. Without planning permission, nothing may go beyond a wall forming a side elevation of the original house, and nothing of more than one storey may extend beyond its rear wall.
Away from them, Class A lets a single-storey addition reach 4 metres beyond the rear wall of a detached house, or 3 metres for other houses; a side extension may be no wider than half the original house; and buildings other than the original house may not cover more than half the curtilage.
The two Residential Areas of Exceptional Character are tested harder still. Policy H10 asks that the siting of any extension follows the spacing and layout of the houses around it, that its design is of a high standard compatible with nearby development, and that features such as trees, hedges, verges and the absence of kerbs are kept; the extensions guide warns that even greater gaps to the boundary than one metre may be required there.
For the Hillcrest Way area, the 2017 Townscape Character Study notes that some newer developments run close to the side boundaries, leaving little room for planting and weakening the landscape. We treat a generous flank gap as part of the design, not a concession.
Sources: 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); legislation.gov.uk: GPDO 2015 (SI 2015/596), Schedule 2 Part 1, development within the curtilage of a dwellinghouse (latest available revised); South Bucks District Council: South Bucks District Local Plan, adopted March 1999, consolidated September 2007 and February 2011; Chiltern and South Bucks District Councils: Chiltern & South Bucks Townscape Character Study Part 3, South Bucks settlements (November 2017)
Green Belt, flood risk, trees and neighbours
Gerrards Cross itself is excluded from the Green Belt, which wraps around it, but houses beyond the settlement's edge are governed by saved policy GB10. National policy accepts an extension there only if it is not disproportionate to the original building, which means the building as it stood on 1 July 1948, or as first built if later. How GB10 measures size is set out on our South Bucks page.
Along the eastern boundary the River Misbourne leaves several properties and land in Flood Zone 3a. For a simple, low-risk development like a house extension, the Environment Agency's flood map for planning says owners may be able to prepare the flood information themselves; we include it with the drawings.
Trees weigh as much as brick in this town. The neighbourhood plan wants protected trees and hedgerows retained and enough space left for the crowns and roots of existing trees, and the extensions guide observes that keeping trees and hedges often reduces an extension's impact on the area around it.
The plan also makes surface water the developer's responsibility, to be drained to ground, a watercourse or a surface water sewer and never to the foul sewer. Building near or on a shared boundary means notifying the neighbours under the party wall rules, which sit apart from both planning and building regulations.
Sources: South Bucks District Council: South Bucks District Local Plan, adopted March 1999, consolidated September 2007 and February 2011; MHCLG (GOV.UK): NPPF Chapter 13, Protecting Green Belt land (GB1-8) (August 2026); Chiltern and South Bucks District Councils: Strategic Flood Risk Assessment Level 1 (December 2018); Environment Agency (GOV.UK service): Get flood risk information for planning in England (Flood map for planning); Gerrards Cross Town Council / Buckinghamshire Council: Gerrards Cross Neighbourhood Plan 2017-2040, Made Plan (December 2025); GOV.UK: Party walls and building work - overview; GOV.UK: Party walls and building work (printable guide)
Designing and building a Gerrards Cross extension
For an extension in Gerrards Cross, our London team brings the whole design in house: architects and designers draw the scheme, structural engineers size the foundations and steel, and Hampstead Chartered Surveyors & Building Consultancy surveys the existing house. We submit the planning application to Buckinghamshire Council, and building regulations approval comes through Buckinghamshire Council's building control service or a private registered building control approver.
The plot is drawn first: flank gaps, the neighbours' nearest windows, the trees and their roots, the drive and the levels. The extension is shaped within those lines before a single room is planned.
Brick, tile and joinery samples are compared on site against the house itself, and where a match is uncertain we detail the junction so that the change of material reads as intended.
Design and management run from our Finchley Road studio in Hampstead, NW3, with no premises in the county; the project manager who planned the sequence of work is the one you meet on site.
Outside Gerrards Cross, and in London rather than Buckinghamshire: 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; Hampstead Renovations: Meadway, NW11 case study
House Extensions in Gerrards Cross: Questions
Is my Gerrards Cross house in the Green Belt, and what is the council's test for an extension?
Probably not if it stands within the town, because the 1999 plan lists Gerrards Cross among the settlements excluded from the Green Belt. Houses beyond that edge are in it, and there saved policy GB10 applies, read with the national policy that an extension must not be disproportionate to the original building. We check the line for your address; the test itself is explained on our South Bucks page.
Does an extension in one of Gerrards Cross's conservation areas need planning permission?
Often it does. A conservation area counts as article 2(3) land, where the householder right does not cover an extension beyond a side wall of the original house or one of more than one storey beyond its rear wall. A single-storey rear addition within the national limits can still be permitted development, though the appraisal lists flat-roofed side extensions among the threats to the Centenary area.
What does the Gerrards Cross Neighbourhood Plan say about extensions?
It works with the 1999 extension policies rather than replacing them, listing H11 on alterations and extensions and GB10 for the Green Belt among the saved policies it relies on. Its own policies add design expectations for residential schemes in the settlement, protection for trees and hedgerows, and conservation of heritage assets above and below ground, which matters near Bulstrode Camp.
How does flood risk affect an extension in Gerrards Cross?
River flooding is mapped along the eastern edge, where the Misbourne leaves several properties and land in Flood Zone 3a. The Environment Agency's flood map for planning shows whether your address needs flood information with the application, and for a simple extension owners can often prepare it themselves. Rainwater from the new roof has to drain to ground, a watercourse or a surface water sewer, not the foul sewer.
Who signs off building regulations for an extension in Gerrards Cross?
The Building Regulations 2010 cover the extension of buildings, so the work is checked by Buckinghamshire Council's building control service or by a private registered building control approver. A small single-storey domestic extension can go in on a building notice, and some conservatories and porches may be exempt; for anything larger we normally submit full plans.
How should I prepare my Gerrards Cross home for a feasibility visit about an extension?
Have the title plan to hand, with any earlier planning decisions and drawings and a note of past extensions and their dates, since at the edge of town the Green Belt test starts from the house as it stood on 1 July 1948. Clear a way to the garden boundaries and any manholes so we can see the levels, trees and drainage.
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