House
extensions
in Great Missenden, HP16

Both village points fall within the Chilterns National Landscape on Natural England's own map, which makes a house at either one article 2(3) land. On such land the Class A householder rights stop at the side walls of the original house, so nothing may project past one without consent, and no addition taller than one storey may project past the original back wall.

Ground-floor additions at the back are still possible without applying, up to the ordinary depths: four metres out from a detached house and three from any other kind, because the larger allowance does not reach article 2(3) land. Any earlier addition the new work joins onto is counted in when the side and two-storey limits are measured.

Outside finishes on permitted work have to look like the house's existing ones, and on this land the rights do not stretch to facing any wall in stone, render, timber boarding, plastic or tile.

Sources: Natural England Open Data: Areas of Outstanding Natural Beauty (England), point query at the OS Open Names point for Great Missenden; Natural England Open Data: Areas of Outstanding Natural Beauty (England), point query at the OS Open Names point for Prestwood; 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)

Within the village envelope the test is Policy H13: no significant harm to the neighbours' amenities, and nothing that spoils the look of the street or locality. Policy H14 spells the harm out as an overbearing bulk, a marked loss of daylight to next door's garden or main windows, or a marked loss of privacy.

Policy H15 deals with design. The addition should keep to the proportions of the house and stay below its height, with outside materials, windows and doors that match or sit comfortably with the original. Upstairs additions normally get a hipped or pitched roof joined into the main one, while a ground-floor addition may have a flat top unless it would stand out from the street or another public place.

In the old village, where the Great Missenden Village Centre conservation area applies, Policy CA1 goes further and refuses an extension that would leave the area's character or appearance neither preserved nor enhanced.

Sources: Chiltern District Council: Chiltern District Local Plan, adopted 1 September 1997 (alterations 29 May 2001; consolidated September 2007 and November 2011)

Past the edge of the built-up area the Green Belt chapter of the 1997 plan applies. Its Policy GB4 lists particular frontages of houses inside the Green Belt; locally they include London Road with Rookwood Way, Wycombe Road at Prestwood and the houses at Peterley. Extensions on those frontages come under Policy GB12, which sends them back to the ordinary H13 to H17 policies.

Further out, Policy GB13 lets an extension through only if it stays subordinate in size and scale to the original dwelling and does not intrude on the landscape, adding any earlier extensions into that judgement. The national test of a disproportionate addition looks back to the building that stood on 1 July 1948, or to the building as first put up where it is newer. Our Chiltern page has the full tests.

Sources: Chiltern District Council: Chiltern District Local Plan, adopted 1 September 1997 (alterations 29 May 2001; consolidated September 2007 and November 2011); MHCLG (GOV.UK): NPPF Chapter 13, Protecting Green Belt land (GB1-8) (August 2026)

Big sheets of glass are the commonest sticking point. The board's lighting guidance doubts that glazed gables or floor-to-ceiling glass will be acceptable in the National Landscape without a design that holds back light spill, and names recessed windows, generous eaves and anti-reflective glass among the remedies. Its design guide wants extensions kept to the back, out of public view, and counts PVC conservatories as inappropriate.

Church Street is the place to be careful. The 2018 assessment counts several of its properties in Flood Zone 2, and Policy GC12 guards the Misbourne's character and banks against harmful building. The Environment Agency's planning flood map shows which zone a plot is in, and for something as simple and low-risk as a house extension the Agency says owners may be able to write the flood risk assessment themselves.

Building close to or on a shared boundary means telling the neighbours first. Extending a building sits squarely within the Building Regulations 2010, so structure, insulation and drainage are checked by Buckinghamshire Council's building control service or by a private registered building control approver.

On an extension here our London team carries the whole job: its in-house architects and designers draw the scheme, its structural engineers size it, and Hampstead Chartered Surveyors & Building Consultancy surveys the house. The application goes to Buckinghamshire Council, and the build is run from the Finchley Road studio in Hampstead, NW3.

Outside Great Missenden, 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: Chilterns Conservation Board: Chilterns Lighting Planning Guidance (June 2025); Chilterns Conservation Board: Chilterns Buildings Design Guide (published February 2010); Chiltern and South Bucks District Councils: Strategic Flood Risk Assessment Level 1 (November 2018); Chiltern District Council: Chiltern District Local Plan, adopted 1 September 1997 (alterations 29 May 2001; consolidated September 2007 and November 2011); Environment Agency (GOV.UK service): Get flood risk information for planning in England (Flood map for planning); GOV.UK: Party walls and building work - overview; GOV.UK: Building regulations approval - when you need approval; GOV.UK: Building regulations approval (printable guide); legislation.gov.uk: The Buckinghamshire (Structural Changes) Order 2019 (SI 2019/957), Part 2, as made (22 May 2019); Hampstead Renovations: Meadway, NW11 case study