An extension adds floor area, and in Chesham it now has a written design code to satisfy as well as the building regulations. We handle the build: foundations, structure, roof, envelope, and the building control application and inspections. We appoint a structural engineer for the steelwork and build to their calculations, and we never produce those calculations ourselves. This page covers the local planning framework, the material and roof rules, the ground and radon position, and the inspection programme.
Chesham now has its own neighbourhood plan and design code
The Chesham Neighbourhood Plan 2024 to 2040 was approved at a referendum on 6 November 2025, with 89 per cent of votes cast in favour of Buckinghamshire Council using it to decide planning applications in the parish. Policy CHESH4 requires development proposals in the defined Chesham Design Code Area to respond positively to the relevant development and design principles in the Chesham Design Code. The code applies mainly to the Tightly Formed Centre, Town Centre Fringes and Suburban Roads design character areas, and does not cover the modern outer suburbs of the town.
Two wider constraints sit around all of it. Growth around Chesham was restricted by the designation of the Metropolitan Green Belt in 1958, and restricted again by its extension in 1972. Buckinghamshire Council's published list of current Article 4 Directions covers nine locations across the county, and none of them is in Chesham.
The design code names the materials a street facing elevation may use
The Chesham Design Code states that only brick, timber, flint, painted brick or painted render will be permitted for street facing facades. It allows systems that accurately mimic them, such as mathematical tiles or brick slips. It also requires all bricks on building facades or street facing elevations to be moulded or stock bricks, and states that wire cut or extruded bricks must not be used where they are visible.
Roofs are covered as well. The code requires roof tiles to be plain clay tiles or slate tiles, and states that pan tiles, concrete tiles and plastic tiles must not be used. It gives the historic roof pitch used in Chesham and the Chilterns as either 42.5 degrees or 47.5 degrees, and says new roof pitches should never be lower than 40 degrees. That floor of 40 degrees sets your ridge height, which belongs on the drawing rather than on site.
Foundations and radon both depend on where in the town you are
The British Geological Survey maps the bedrock beneath Chesham town centre and the floor of the Chess valley as the New Pit Chalk Formation. It describes that formation as principally blocky, white, firm to moderately hard chalk with numerous marls or paired marl seams. On the plateau ground above the town at Botley, Chartridge Lane and Asheridge, the mapped superficial deposit is the Clay-with-flints Formation. The survey describes that as unbedded and heterogeneous, dominated by orange brown and red brown sandy clay with abundant nodules and rounded pebbles of flint.
Radon varies across the town too. The BGS Radon Indicative Atlas gives a maximum radon potential of 5 to 10 per cent for the one kilometre squares covering northern and north western Chesham. It gives 1 to 3 per cent for the squares covering the south and east of the town. UKHSA states that when extensions are made to existing buildings in high radon areas, the Building Regulations require protective measures against radon entering the building.
Buckinghamshire Council's own building control service inspects the work
Buckinghamshire Council runs its own building control service, and site inspections in Chesham are booked through the former Chiltern and South Bucks district area booking form. The council states that a house extension normally requires five building control inspections, and that the number is usually agreed before work begins. It names foundations, damp proofing, roof structure and drainage as intermediate stages, alongside the completion inspection.
Those stages are the spine of the programme. We make the application, agree the inspection stages with the council before work starts, and book each visit so the trench, the membrane, the roof structure and the drains are all seen open. Covering work before it has been inspected is the expensive mistake on an extension.
- Roof works and structural alterations at roof level
- Levels, drainage and landscaping made good around the new build
- Full fit-out, finishing and making good
- Drainage diversion and build-over agreements with the water authority
- Bi-fold, sliding and French door openings to the garden
The GS Renovation Difference in Chesham
An extension in Chesham is now judged against design rules written down locally rather than left to officer judgement. That helps if you read them early, because the code decides what a street facing elevation can be built and roofed in, and those are drawing decisions rather than first fix decisions. We coordinate the building control application and the inspections, agree the stages with the council before work starts, and appoint the structural engineer for any steelwork. We never produce structural calculations ourselves. GS Renovation Ltd is fully insured, registered in England, company number 14611254, and quotations are free and without obligation.
- Free follow-up visit after completion if anything needs attention
- Building control applications and inspections coordinated for you
- Aftercare and snagging support once the job is finished
- Building control inspected at foundation, damp course and steel stages
- Scaffolding and site set-up planned for tight London plots
- Insulation and thermal detailing to current regulations