Appeal 6004187

The appeal is dismissed.

On 16 December 2025 the Government published a consultation National Planning Policy Framework (the Framework). Whilst the format of the consultation version of the Framework is modified, the policies guidance pertinent to this appeal, including that relating to the extension or alteration of an existing building in the Green Belt remain unchanged, except for their regrouping and renumbering. Therefore, there is no need to invite further comments from the Council or the appellant on the revisions as they do not affect this appeal. Where references are made to paragraph numbers of the Framework, these relate to the December 2024 version.

The main issues are: • whether or not the proposal would be inappropriate development in the Green Belt; • the effect on the openness of the Green Belt; and • whether any harm to the Green Belt by reason of inappropriateness is clearly outweighed by other considerations so as to amount to the very special circumstances necessary to justify it.

The Framework identifies that the fundamental aim of Green Belt policy is to prevent urban sprawl by keeping land permanently open. It goes on to state that inappropriate development is, by definition, harmful to the Green Belt and should not be approved except in very special circumstances. Development within the Green Belt is regarded as inappropriate, subject to a number of exceptions listed in paragraphs 154 to 156 of the Framework. One such exception, at paragraph 154(c), is the extension or alteration of a building, provided that it does not result in disproportionate additions over and above the size of the ‘original building’1.

Policies GB1 and GB10 of the South Bucks District Local Plan (adopted March 1999, consolidated September 2007 and February 2011) (SBLP) indicate that if extensions, together with all previous extensions, are of a small scale in relation to the original dwelling they will normally be permitted in the Green Belt. The supporting text explains that in this connection, extensions or alterations which would result in the original dwelling having increased its floor space by more than half will not be regarded as small scale.

The Framework does not provide a definition of what would amount to a ‘disproportionate’ addition over and above the size of the original dwelling. Whilst the wording in policies GB1 and GB10 is slightly different to the Framework, defining disproportionate as ‘small scale’ extensions to the original building, I find the two policies to be broadly consistent with the Framework, insofar as they pertain to residential extension in the Green Belt.

The appeal property is a detached, two storey dwelling which has been subjected to various extensions and alterations.

Including the floorspace of the property’s garage, the officer’s delegated report assesses the original dwelling as having an approximate floor area of 140sqm which has subsequently been extended over time resulting in a floorspace of approximately 375sqm, or 168% over and above its original size. The appeal scheme would increase the size of the single storey ground floor extension by approximately 12sqm, resulting in a dwelling which has a floor area of approximately 387sqm. The delegated report says this would equate to a 176% enlargement of the original dwelling.

I note the appellant has queried the veracity of the figures in the officer’s delegated report, suggesting that other historic alterations or lawful development may exist beyond the single permission2 referenced by the Council. However, in the absence of any alternative calculations or plans to the contrary provided by the appellant, I have relied upon the calculations provided by the Council.

Based on the above, I find that the totality of the appeal proposal and the previous extensions to the building would result a significant increase in the size of the original building which would amount to disproportionate additions over and above the size of the original building. The proposal would therefore be inappropriate development in the Green Belt as defined by Policies GB1 and GB10 of the SBLP and the Framework.

In coming to this conclusion, I have considered the four appeal decisions provided by the appellant in support of the proposal. [name] accept floorspace is one aspect of determining proportionality, with respect of the extension to Chedley3, when combined with previous extensions, that proposal resulted in overall additions that 1 [name] 2: Glossary of the NPPF: Original building: A building as it existed on 1 July 1948 or, if constructed after 1 July 1948, as it was built originally. 2 Application Reference 94/00139/FUL 3 Appeal Ref: APP/N0410/D/24/3349362 were much less than in this appeal scheme before me (81% increase as opposed to 176%). It is therefore not directly comparable.

In respect of the other three appeal decisions put to me, whilst the Inspector described the extension to Nuestras4 as “a fairly significant increase” there is little to no empirical evidence in that decision to help me understand the scale of the extensions. The same is true for the Trees5 and Mull Cottage6 appeal decisions. In the absence of empirical evidence or any plans to show the original dwelling relative to the extensions already carried out and the proposed extensions for any of the three appeal decisions, I cannot make a proper comparison in relation to this appeal.

Consequently, none of appeal decisions cases referred to by the appellant have led me to alter my overall decision.

Openness is an essential characteristic of the Green Belt that has spatial as well as visual aspects.

As it would increase the volume and massing of the existing property the development would inevitably have an effect on the spatial openness of the Green Belt. There would also be a material impact on the visual openness of the Green Belt.

However, as the extension would be single storey and would be contained within the small space in between two existing two storey rear additions it would be screened on three sides by the existing property. The fourth side would consolidate the existing rear elevation and would be concealed to a great extent by the property’s well vegetated garden boundaries and adjacent woodland. The extension would therefore not be prominently visible to the adjoining neighbour or discernible beyond the property’s boundary.

For these reasons, whilst the proposed development would impact both the spatial and visual openness of the Green Belt, given the above mitigating factors, I find that it would result in very minor harm to the openness of the Green Belt. Nevertheless, this harm still weighs against the proposal.

The appellant contends a fallback position exists whereby a ground floor extension could be built under permitted development rights7 which would be similar in size to the appeal development, apart from providing a 10mm standoff from the existing rear additions. Following its construction, the appellant suggests that planning permission could be secured to join the extensions together, and that this would result in the same development as the proposal.

Having regard to the relevant case law, if the development taking place is more than a theoretical possibility, then it is material. Secondly, only if it satisfies that requirement does any assessment of its weight fall to be determined. 4 Appeal Ref: APP/N0410/D/22/3292666 5 Appeal Ref: APP/N0410/D/25/3369282 6 Appeal Ref: APP/N0410/D/22/3310838 7 Schedule 2, Part 1, Class A of The Town and Country Planning (General Permitted Development) (England) Order 2015 (as amended).

I have not been provided with any plans to show the original building, nor have I been provided with a plan to show how the fallback could be built under Class A. For these reasons I cannot be certain that there is a realistic prospect of such a fallback, and that it would result in the same or greater harm than I have identified with the scheme before me. Consequently, this limits the weight I can attribute this purported fallback position as a very special circumstance in favour of the appeal scheme.

I have found that the proposal would be inappropriate development in the Green Belt contrary to Policies GB1 and GB10 of the SBLP and the provisions of the Framework. The proposal would also result in very minor harm to the openness of the Green Belt.

The Framework requires that any harm by reason of inappropriateness be given substantial weight and that inappropriate development should not be approved except in very special circumstances. Very special circumstances will not exist unless the harm to the Green Belt and any other harm is clearly outweighed by other considerations.

In this case, I find that the weight of these other considerations does not clearly outweigh the harm arising to the Green Belt. Consequently, the very special circumstances that are necessary to justify inappropriate development in the Green Belt do not exist.

The proposal conflicts with the development plan taken as a whole and there are no material considerations, including the Framework, to suggest the decision should be made other than in accordance with the development plan. Therefore, for the reasons given, and having regard to all other matters raised, the appeal is dismissed.