Which Old District Guide Applies to My Extension in Buckinghamshire?

A householder design guide is a supplementary planning document (SPD) or guidance note that explains how the council applies its Local Plan design policies to extensions, lofts and outbuildings. It is not law and it is not a plan policy, but officers weigh it when they decide your application.

Key Takeaways

• Find your former district first: that decides which of the four guides applies.
• Wycombe (2020), Chiltern (2013), South Bucks and Aylesbury Vale (2023) each have their own householder guide.
• All four expect first-floor side extensions to keep a gap to the boundary, usually at least 1 metre.
• Light tests differ: Wycombe and South Bucks use 60 and 45-degree lines; Aylesbury Vale uses 45 degrees; Aylesbury Vale and Wycombe set rear depth limits.

How do I know which former district my house is in?

The four districts were Wycombe, Chiltern, South Bucks and Aylesbury Vale. As a rough guide from the towns we cover: High Wycombe and Marlow sit in the former Wycombe district, Amersham and Chesham in Chiltern, Beaconsfield and Gerrards Cross in South Bucks, and Aylesbury in Aylesbury Vale. Village boundaries are less obvious, so check the former district against the council's own map or a recent decision notice for a neighbouring house: it names the local plan the officer applied, which tells you the district.

The guides at a glance:

Former district	Guide	Date	First-floor gap to side boundary	Light test to neighbours	Rear depth
Wycombe	Householder Planning and Design Guidance SPD	January 2020	At least 1 m	60° single storey, 45° two storey	Half the original house's depth
Chiltern	Residential Extensions and Householder Development SPD	September 2013	At least 1 m where gaps are modest, more where wider	Judged on outlook and light, no fixed angle	Keep a garden of 15 m or more at that depth
South Bucks	House Extensions Design Guide	Not dated on the document	At least 1 m	60° single storey, 45° first floor and two storey	No fixed figure
Aylesbury Vale	Vale of Aylesbury Design SPD	2023	Generally not less than 1 m in urban areas	45° line	Normally 3 m terraced, 4 m semi

What does the Wycombe guide test?

The Wycombe area's Householder Planning and Design Guidance SPD was adopted in January 2020 and applies to all householder development in the former district (Wycombe Householder SPD). Its figures:

• Side extensions: at least 1 metre between the extension and the boundary at first floor, more on a spacious plot (section 9.5).
• Rear extensions: no deeper than half the depth of the original house, and, with earlier extensions, no more than half the depth of the original rear garden; a lesser depth next to a shared boundary on semis and terraces (section 10.6).
• Light: a line from the mid-point of the neighbour's nearest habitable room window at 60 degrees for single storey rear extensions and 45 degrees for two storey ones. How far the extension crosses that line shows how much light may be lost (section 14).
• Dormers: on the rear where possible, set below the ridge, at least 1 metre above the eaves, at least 1 metre from the roof edge on a gabled roof and 0.5 metres from the hip (section 11).
• Privacy: side windows that would overlook a neighbour's garden obscure glazed and non-opening up to 1.7 metres above floor level, and 25 metres between the backs of houses unless design prevents overlooking (section 16).

What does the Chiltern guide test?

The Chiltern Residential Extensions and Householder Development SPD dates from September 2013 (Chiltern SPD). It sets fewer fixed numbers than Wycombe and leans on the character of the street:

• Rear extensions: should not take a disproportionate amount of garden. Where the garden is 15 metres deep or more, a single storey extension should not reduce that depth, especially where gardens in the area are long (paragraph 32(i)).
• Two storey side extensions: set in from the boundary at first floor by at least 1 metre where gaps between houses are modest, and by "significantly more" where they are wider (paragraph 34(i)).
• Side windows: none in a side wall built close to a common boundary (paragraph 32(iii)).

Inside the Chilterns National Landscape the SPD also points to the Chilterns AONB Buildings Design Guide for materials, and Green Belt rules sit on top; see our Buckinghamshire Green Belt post.

What does the South Bucks guide test?

The South Bucks House Extensions Design Guide is based on the old South Bucks District Local Plan policies H10 to H13, EP3 and GB10 (South Bucks Design Guide). It says:

• One metre rule: two storey extensions, or any extension at or above first floor, at least 1 metre from the flank boundary, to stop a terracing effect. More may be needed in a Residential Area of Exceptional Character (paragraph 3.1).
• Roofs: a two storey extension's roof should match the house; flat roofs on two storey extensions are unacceptable (paragraph 3.2).
• Light: extensions should project no further than a 60-degree line for single storey and 45 degrees for first floor and two storey, drawn from the mid-point of the nearest ground floor habitable room window next door. Kitchens, living rooms and bedrooms count; bathrooms, halls and landings do not (paragraph 7.5).

What does the Aylesbury Vale guide test?

The Vale of Aylesbury Design SPD was adopted in 2023 and covers far more than extensions; chapter 8 deals with household extensions (Vale of Aylesbury Design SPD). It is the only one of the four that caps the depth of a rear extension itself in metres:

• Rear depth (Principle DES62): normally no more than 3 metres from the original rear wall for a terraced house and 4 metres for a semi-detached house.
• Two storey rear: not normally permitted if any part crosses a 45-degree line from the centre of the nearest habitable room window next door.
• Side extensions (Principle DES60): subservient and set back from the front; a gap to the boundary generally not less than 1 metre in urban areas, or the first floor set back at least one third of the house's depth.
• Front extensions (Principle DES61): not normally beyond a 45-degree line from the nearest neighbouring window; halls, bathrooms and utility rooms are discounted.

For example (illustrative, not a real job): a semi-detached house in Aylesbury and an identical semi in Marlow both want a 5 metre single storey rear extension needing planning permission. In Aylesbury, DES62's 4 metre norm means the drawings must justify the extra metre. In Marlow, the Wycombe guide asks instead that a rear extension is no deeper than half the depth of the original house, so on a house 9 metres deep the 5 metre extension also needs justifying, and the 60-degree line from the neighbour's window is tested too.

Do I need planning permission at all?

Not always. None of these guides decides that: national permitted development rights do, and they still apply in Buckinghamshire unless an Article 4 direction, a planning condition or the house being a flat removes them. In a conservation area or the Chilterns National Landscape the national rules are tighter: side extensions, two-storey rear extensions and roof enlargements need permission there (GPDO 2015, Schedule 2, Part 1). A single storey rear extension within the national limits needs no application. Check your project with our tool before paying for drawings.

How long does Buckinghamshire take to decide?

Buckinghamshire decided 842 of 1,361 householder applications within 8 weeks without an agreed extension of time between 1 July 2025 and 30 June 2026, and made 1,494 of its 2,855 householder decisions under an agreed extension (MHCLG live table PS2). Allow for a request for more time in your programme.

Our Buckinghamshire Council page covers validation and fees, and the Buckinghamshire page the wider county. Planning drawings for an extension are £895 on our house extensions page. Town examples are in our posts on Amersham and Aylesbury.

Frequently asked questions

Has Buckinghamshire Council replaced the old district guides with one county guide? Not for householder design. The council's local planning guidance page still lists the Wycombe, Chiltern, South Bucks and Aylesbury Vale documents separately.

Is the 1 metre gap a strict rule? No. Each guide presents it as a design expectation, and South Bucks says it can be waived next to land that will stay open, such as a field or a road. Officers still expect a reason if you build closer.

Does the 45-degree line apply to single storey extensions? It depends on the district. Wycombe and South Bucks use a wider 60-degree line for single storey extensions; Aylesbury Vale applies 45 degrees to two storey rear and front extensions.

Which guide applies if my house is in a conservation area? The district guide still applies, alongside the conservation area appraisal and the heritage policies of the local plan, which usually ask for more care with materials and visible changes.