Extension plans for an Amersham house cost £645 drawings + £150 survey (£795 total) with us, fixed, from the measured survey to submission and the case officer's questions. Buckinghamshire Council's own householder fee is £548 on top. What changes from one Amersham house to the next is not our fee but how much the drawings have to prove, and that depends on which of the town's several characters your street belongs to.
On this page
Which Amersham is your house in?
Amersham is two towns that grew into one. The Old Town sits in the Misbourne valley. Amersham-on-the-Hill grew up around the station after the railway arrived in 1892, slowly at first and then quickly in the 1920s, when the "Metro-land" idea brought estates built mainly in the Arts and Crafts style (Buckinghamshire Historic Towns Assessment). That history is written into the planning map.
Buckinghamshire Council lists four conservation areas in Amersham: the Old Town, Elm Close, the Weller Estate and Shardeloes Parkland (council list). The first three cover houses people extend:
- Old Amersham, designated in 1969, covers the High Street, part of Whielden Street and Church Street, and the long burgage plots behind the High Street houses.
- Elm Close, designated in 1992, is thirty Arts and Crafts semi-detached houses built in the early 1920s as social housing around a central green.
- The Weller Estate, also designated in 1992, protects early development by the Metropolitan Railway's estate company. Highfield Close, a triangle of matching 1930s semis around a green, is part of it.
Outside those boundaries, most of Amersham-on-the-Hill is ordinary residential street, and an extension there follows the general householder guidance.
What guidance will the council use?
Buckinghamshire Council replaced four district councils in 2020, but it still judges extensions against the old district guides. For Amersham that is the former Chiltern District's Residential Extensions and Householder Development SPD of September 2013 (Chiltern SPD). Its tests for two-storey side extensions are about gaps between houses. Where houses stand in a visual row with modest gaps, the first floor should be set in at least 1 metre from the boundary. Where gaps are wider, the SPD expects "significantly more than 1 metre". Eaves and ridge heights should match the existing house.
That matters on the Hill, where many 1930s semis have generous side gaps. A side extension that would pass on a tighter street can be refused for closing a gap that the street's rhythm depends on.
How does a conservation area change the drawings?
In Old Amersham, an extension is usually at the back, on a narrow plot, behind a listed or historic frontage. The council will want to see the roof, the materials and the relationship with the old building drawn accurately. Our drawings show existing and proposed elevations of every affected side, and where a heritage asset is involved Buckinghamshire's validation list asks for a heritage statement. That is a separate document, from £565 with us. Check whether your house is also listed before you plan anything. A listed house needs listed building consent as well as planning permission.
On Elm Close and the Weller Estate the issue is uniformity. These estates were designed as sets of matching houses, so the drawings need to show how a rear or side extension keeps the roof form, window pattern and brick or render of its neighbours. Front and side additions visible from the green are the hardest to justify.
What if the house is in the Green Belt?
The built-up area of Amersham is excluded from the Green Belt, so most houses in town are not affected. Houses on the edges of town, and in the surrounding hamlets, often are, and the Chiltern SPD notes that a large part of the former district is Metropolitan Green Belt.
National policy allows an extension in the Green Belt only if it is not disproportionate to the original building. The original building means the house as it stood on 1 July 1948, or as first built if later (NPPF Chapter 13, GB7). The SPD adds that the council counts every earlier extension towards that total. For a Green Belt house, Buckinghamshire asks for floor plans showing the measured volume of the gross external area (council validation guidance). We read the planning history first. If a previous owner has already used most of the allowance, we tell you before you pay for design.
Does the Chilterns National Landscape matter?
The Chilterns Area of Outstanding Natural Beauty, now called a National Landscape, wraps around the town. In one recent Amersham decision, the council described the boundary as wrapping round a site in the Misbourne valley to the south and east, and applied Core Strategy Policy CS22, which protects the setting of the area and the views into and out of it (committee report, PL/21/1309/FA). National policy says development inside protected landscapes should be limited in scale, with substantial weight on conserving their natural beauty (NPPF Chapter 19, N4).
For a house inside the boundary, permitted development rights are narrower, and the SPD points owners to the Chilterns Buildings Design Guide for materials such as flint and local brick. We confirm which side of the line your house is on before the first sketch.
How long will Buckinghamshire take, and what is the total?
In the year to 30 June 2026, Buckinghamshire decided 842 of 1,361 householder applications within eight weeks, prior approvals excluded (MHCLG live table PS2). That is a slower record than many London boroughs, so allow for more than eight weeks in your building timetable.
- Our planning drawings and submission: £645 drawings + £150 survey (£795 total).
- Buckinghamshire Council's householder fee: £548.
- A heritage statement, where the house is in a conservation area or near a listed building: from £565.
- After approval, building regulations drawings and structural calculations. Our planning, building regulations and structural package is from £1,245 drawings + £150 survey (£1,395 total) for one extension.
Our Buckinghamshire Council page sets out the council's validation rules, and the Buckinghamshire page covers the county. For a two-storey scheme in the next town up the valley, see two-storey extension plans in Chesham. For a loft in the Wycombe area, where a different guide applies, see loft conversion drawings in High Wycombe.
Frequently asked questions
Is all of Amersham-on-the-Hill a conservation area? No. Only the Weller Estate and Elm Close are, plus Shardeloes Parkland on the edge of the Old Town. Most streets on the Hill are outside any conservation area, though the council still expects an extension to respect the street.
Does the Wycombe householder guide apply in Amersham? No. Amersham was in the former Chiltern District, so the Chiltern Residential Extensions and Householder Development SPD (2013) applies.
How does the council measure a Green Belt extension? Against the house as it stood on 1 July 1948, counting earlier extensions. Your floor plans must show the measured volume, and we prepare the original, existing and proposed figures.
Can I extend a house in Old Amersham at all? Often yes, usually at the rear. The drawings must show how the extension sits behind the historic frontage, and a heritage statement goes with the application.
If the application goes through the Planning Portal, the Portal adds its own service charge: nothing, £99 or £149 including VAT, depending on the application type and complexity, paid to the Portal at submission and not normally refunded with a council fee (Ashford Borough Council, Planning Portal service charges, 11 September 2026). It is not ours and not the council's. Other submission routes exist; where your council accepts one without a charge, we can use it.
