House Extensions Amersham

Amersham's built-up area is excluded from the Green Belt, which changes the question you are asking. Inside the town the local plan's ordinary extension policies apply rather than the tighter Green Belt rules. Those policies are specific about roof form, materials and side boundaries, so the design work is worth doing properly before anyone prices a foundation.

For Amersham, on London-derived ranges a single-storey rear extension typically starts from £40,000, or £2,000 to £2,800 per m²; Buckinghamshire work generally runs below that. GS Renovation Ltd, a building contractor based in Potters Bar, does the work in Amersham: the structural engineer we appoint designs the structure, we build it, and building control signs it off.

The Green Belt stops at the edge of the built-up area

Amersham's built-up area is excluded from the Green Belt, though it is enclosed by it. The adopted local plan lists the built-up areas of Amersham and Chesham Bois among those excluded, so the plan's ordinary built-up area extension policies apply inside the town rather than the Green Belt rules that apply outside it.

There is also no neighbourhood plan for Amersham. Buckinghamshire Council's list of neighbourhood plans carries no Amersham entry, while neighbouring Chesham Bois and Little Chalfont sit at the neighbourhood area designation stage. That leaves the Chiltern District Local Plan, adopted on 1 September 1997, as the document your design is measured against.

Housing in Amersham

For Amersham the Council Tax list gives about 7,670 homes; by type 22% flats and 78% houses, by age 68% post-war, 21% interwar and 11% older than 1919. A detached house in Amersham often extends far enough from the boundary that no party wall notice is needed, and 31% of homes here are detached.

What Policies H15 and H17 ask of an extension

Roof form comes first. Under adopted Policy H15 a two storey or first floor extension should normally have a hipped or pitched roof integrated into the existing roof. A flat roofed one will not be permitted unless it is surrounded by existing pitched roofs, is subordinate to the main roof, and is not prominent in the street scene or locality.

Policy H15 also requires that external materials, windows and doors match or harmonise with those of the existing dwelling. Policy H17 allows a single storey side extension to be built up to the side boundary. The exception is areas characterised by spacious layouts, where relatively large distances matter in the street scene and a gap must be kept.

The ground the foundations go into

It depends which of the two Amershams you are in. Across Amersham-on-the-Hill the British Geological Survey maps the Clay-with-flints Formation over chalk bedrock, at Sycamore Road, Hill Avenue, Woodside Road, Chestnut Lane and Highfield Close. BGS describes that formation as orange-brown and red-brown sandy clay with abundant nodules and rounded pebbles of flint, up to about 10 metres thick.

BGS also notes that the thickness is very variable where the formation has been let down into dissolution pipes in the chalk beneath. On the valley floor the picture differs. Under Amersham High Street the mapped superficial deposit is Alluvium, clay, silt, sand and gravel laid down by the River Misbourne, over New Pit Chalk Formation bedrock. Mapping tells you what to expect. A trial hole on your plot tells you what you have.

Extending a house in Elm Close

The council has already set out what has worked there. Its Elm Close appraisal records that opportunities for sympathetic extension are limited. It also records that several properties have been given two storey side extensions with pitched roofs, set back from the front elevation and with ridge lines below that of the main roof. That is how they stayed subordinate to the original building.

Garages are treated the same way. The houses of Elm Close were built without garages, and every garage added since the 1920s has been placed in a rear garden, which the appraisal asks any further garage to follow. Points like these belong in the conversation with the council before drawings are finalised.

Kitchen extensions in Amersham

72% of the houses in Amersham are semi-detached or detached, which usually leaves room for a kitchen extension across the full rear width, with a steel beam over the opening into the house. The fit-out is priced on its own page, kitchen renovation in Amersham; the build figures are in the table above.

Side return extensions in Amersham

Side returns belong to Victorian and Edwardian terraces, and only 11% of homes in Amersham predate 1919, so they are the exception here; most extensions run across the full rear width instead. Our side return extension page covers the build in detail, with build rates of £2,400 to £3,200 per m².

Double storey extensions in Amersham

Under permitted development a two-storey rear extension can go no more than 3 metres beyond the original rear wall and must stay at least 7 metres from the rear boundary, and in a conservation area it is not permitted development at all. Many gardens are too short for the 7 metre rule, so a double storey extension in Amersham often needs planning permission from Buckinghamshire Council. With 56% of homes here semi-detached or detached, the side of the house is often an option too. Our double storey extension page explains the build, at £1,800 to £2,600 per m² across both floors.

• Drawings and the structural engineer's design coordinated for you
• Party wall process explained, and the extension built to the award
• First fix and second fix plumbing and electrics throughout

VOA Council Tax stock of properties, March 2025, for Old Amersham and Amersham-on-the-Hill & Chesham Bois. Counts rounded by the VOA.

Once you know the scope of the house extensions in Amersham, it helps to read RSJ and steel beam installation in Amersham, house extensions in Chesham, basement extensions, party walls and extensions, how we handle house extensions across London and Permitted Development Rights.

Trusted House Extensions in Amersham

An extension here is a design conversation with the council before it is a building job. We appoint the structural engineer for the foundations, beams and openings, build to the calculations, and coordinate the building control application and inspections. Where the local plan's roof and materials policies or a conservation area shape the design, we build what has been approved rather than improvising on site. Fully insured, with free no obligation quotations.

• Weathertight shell reached before the fit-out begins
• Photographs kept at each stage for your records
• Programme planned around party wall notice periods before excavation near a neighbour

Checked by Abdelaaziz Saaid, founder and director of GS Renovation Ltd (Companies House no. 14611254). Structural design is by the consulting engineer appointed to your project.