Yes, in most cases. But Buckinghamshire Council still applies the Green Belt policy of the old district where your house is, and the three tests are quite different:
On this page
- Former Wycombe district: Policy DM43 sets volume bands. A house of 240 to 720 cubic metres as originally built can grow to its original volume plus 50%.
- Former South Bucks district: Policy GB10 treats an increase of more than half the original floorspace as too big.
- Former Chiltern district: Policy GB13 asks that the extension stays subordinate to the original house, with no figure.
Planning drawings for the application are £645 drawings + £250 survey (£895 total) with us, fixed, survey included. The householder fee of £548 is paid to the council separately.
Which rule applies to my house?
The old district boundary decides. High Wycombe, Marlow, Princes Risborough and the villages around them use the Wycombe District Local Plan, adopted in August 2019. Beaconsfield, Gerrards Cross, Burnham, Farnham Common and the Ivers use the South Bucks District Local Plan of 1999. Amersham, Chesham, the Chalfonts and Great Missenden use the Chiltern District Local Plan of 1997. These old plans stay in force until the new Buckinghamshire Local Plan replaces them.
Then check whether the house is in the Green Belt at all. Many towns and larger villages are excluded from it, such as Marlow Bottom in the Wycombe area and Farnham Common in South Bucks.
How does Wycombe's volume test work?
Policy DM43 is the clearest Green Belt rule in the county. An extension or replacement is acceptable if it meets one of these conditions:
- It accords with a made neighbourhood plan.
- The house is within a built-up village shown on the Policies Map.
- The house is in a ribbon of houses with a built-up frontage, and the result is no bigger than the average volume of its two neighbours.
- The original house is under 240 cubic metres and the result is no more than 360.
- The original house is 240 to 720 cubic metres and the result is no more than the original plus 50%.
- The original house is over 720 cubic metres and the result is no more than 1,080.
- A replacement is no larger than the house it replaces.
Volume means gross external volume, basement included, measured against the house as it stood on 1 July 1948 or as first built (paragraphs 6.228 and 6.229). Existing outbuildings are left out of the sum. Wycombe moved from floorspace to volume because double-height voids and roof designs produced anomalies.
So a semi of 400 cubic metres as built can reach 600. If a 1970s extension already added 120, about 80 cubic metres remain. That is roughly a single-storey rear room of 4 by 7 metres, depending on the roof.
How does South Bucks' floorspace test work?
Policy GB10 permits extensions that are "of a small scale" in relation to the original house. Paragraph 3.45 sets the line: extensions taking the floorspace up by more than half are not small scale, and smaller ones can still fail on design. The original house is the one standing on 1 July 1948, or as first built.
Three details catch people out:
- Everything counts, including basements and extensions built as permitted development (paragraph 3.46).
- Outbuildings within 5 metres of the house, built since it was, count as extensions.
- Roof space is encouraged. Paragraph 3.47 says only work that adds volume, such as dormers, counts. Converting the existing loft does not.
In the Green Belt settlements the plan names, an extension "a little larger" may be allowed (paragraph 3.49).
How does Chiltern's test work?
Policy GB13 permits extensions that are subordinate to the size and scale of the original house and not intrusive in the landscape, with earlier extensions counted together. There is no published percentage, so the case rests on the drawings. Houses in the Green Belt settlements under Policy GB5, such as Jordans, Hyde Heath and Little Kingshill, or the rows of houses under Policy GB4, fall under Policy GB12 instead. That policy does not apply the subordinate test, but it resists extensions that push built form out into open land.
Can I extend without applying?
Sometimes. Green Belt status does not remove permitted development rights, so a single-storey rear extension up to 3 metres on a semi or 4 metres on a detached house can need no application (MHCLG technical guidance). But much of the county's Green Belt is also in the Chilterns National Landscape. There, side extensions, cladding and roof extensions are not permitted development, and the larger home extension prior approval is not available.
Question 1 of up to 4
What type of property is it?
- Property
- Not answered yet
- Area
- Not answered yet
- Work
- Not answered yet
- Route
- Not answered yet
If no application is needed, the checker says so. In South Bucks, a permitted development extension still counts against the half-floorspace cap later.
A worked example
An illustrative example, not a real job: two identical 1930s detached houses of 150 square metres and 450 cubic metres, one near Lane End in the Wycombe area, one outside Burnham in South Bucks. Near Lane End, DM43 allows a total of 675 cubic metres, so 225 more. Outside Burnham, GB10 allows up to 75 square metres more floorspace, minus anything added since, and a loft conversion inside the roof does not count. Same house, different answer, because of a district line drawn decades ago.
How long does Buckinghamshire take?
Buckinghamshire decided 842 of its 1,361 householder applications within 8 weeks without an agreed extension of time between 1 July 2025 and 30 June 2026 (MHCLG live table PS2). Allow for that in your programme.
Council detail is on our Buckinghamshire page and county page. For local cases, see extension plans in Marlow Bottom, Farnham Common and Great Missenden. The service is on our house extensions page.
Work out your fee
FFP-01 · Rev AHouseholder application fee, paid to your council at submission.
Prices include one measured survey of a house of up to two storeys (£250). A flat or maisonette is £50 less; a house of three storeys or more is £50 more. One survey covers every service on the same job.
Plus the Planning Portal's own charge if the application goes through the Portal: up to £149 including VAT, depending on the application type, and some types have none (source).
Get this fee in writingor email hello@fixedfeeplans.co.uk
No obligation. Nothing is sent until you ask; your enquiry comes to us and nowhere else.
Frequently asked questions
Does Buckinghamshire have one Green Belt rule? No. Until the new Local Plan is adopted, the policy of the former Wycombe, South Bucks or Chiltern district applies, depending on the address.
How much can I add in the former Wycombe area? It depends on the original volume: up to 360 cubic metres in total for a small house, original plus 50% for a middle-sized one, and 1,080 at most for a large one.
Does a loft conversion count in South Bucks? Only the parts that add volume, such as dormers. Converting the existing roof space does not count.
Does my garden office count? In South Bucks, if it is within 5 metres of the house. In the Wycombe area, outbuildings have their own limits: 25% of the original volume and 140 cubic metres.
What date is the original house? 1 July 1948, or as first built if later, in all three areas.
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.
