Appeal 3374500

The appeal is allowed and planning permission is granted for proposed alterations to the roof; single storey rear extension and single storey side extension at [site address] , Denham, Buckinghamshire [postcode] in accordance with the terms of the application, subject to the conditions in the attached schedule.

The description of development on the application form is worded differently to the Council’s decision notice. The evidence that I have before me does not provide details of the appellants’ agreement to change the development description, therefore I have used the description of development provided on the application form, which adequately describes the development.

On 16 December 2025 the Government published a consultation National Planning Policy Framework (the Framework). Whilst the format 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.

The main issues are: (i) whether or not the proposal would be inappropriate development in the Green Belt; and (ii) 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 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.

Whilst the Framework does not provide a definition of what would amount to a ‘disproportionate’ addition over and above the size of the original dwelling, Policies GB1 and GB10 of the South Bucks District Local Plan (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. In addition, the appeal property lies within the Denham Green Belt Settlement. In this regard, supporting text to policy GB10 explains that it may be possible to allow some extensions a little larger than would be acceptable elsewhere in the Green Belt, however any such extensions still have to comply with the criteria set out in policy GB10.

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

The officer’s delegated report assesses the original dwelling as having a gross floor area of approximately 166sqm which has subsequently been extended and a detached garage built which cumulatively amount to a gross floor area of approximately 275sqm, or 65% over and above its original size. It then refers to a previously approved scheme2 which would consolidate the development, resulting in a single building with a gross floor area of approximately 274sqm, therefore maintaining the existing 65% increase.

Like the previously approved scheme, the appeal scheme would similarly consolidate the development. However, unlike that scheme, it would increase the size of the single storey ground floor extension by a depth of 1.2m. This would increase the building footprint by approximately 17sqm, resulting in a dwelling which has a gross floor area of approximately 291.4sqm, which would equate to a 75.5% enlargement of the original dwelling.

Based on the above, it is clear that the totality of the appeal proposal would result in a development which is greater than half the size of the original building. For this reason, I agree with the Council that the development would result in disproportionate additions over and above the size of the original building whereby it would be inappropriate development in the Green Belt as defined by Policies GB1 and GB10 of the SBLP and the Framework. 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 Appeal Decision Ref APP/N0410/D/25/3361080 - Application Ref PL/24/2121/FA for the demolition of garage and conservatory, single storey side/rear extension, alterations to existing rear extension.

Openness is an essential characteristic of the Green Belt that has spatial as well as visual aspects. The appeal property is clearly visible from [site address] and [address]. Notwithstanding the existence of other dwellings in the vicinity, the openness of the Green Belt is clearly evident around the property and the wider area.

The development would extend the building to the rear and side which would increase the volume and massing of the existing property and in doing so it would result in a loss of openness.

The appellant contends a fallback position exists whereby a garden room and loft conversion3 could be built under permitted development rights which would result in buildings at the appeal site which would be equivalent in size volumetrically to the appeal development. 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.

Given that the Council have issued a certificate of lawfulness for the garden room and loft conversion I regard the appellant’s garden room and loft conversion as a fallback position were the appeal to be dismissed. Furthermore, I agree with the appellant that as the fallback would result in three separate buildings of the same volume as the appeal scheme (i.e. a garden room, a loft converted house and a detached garage), it would lead to a much greater loss of openness due to the dispersal of the buildings across the site.

For these reasons the appeal scheme would result in a more consolidated development which would have much less impact on the openness of the Green Belt than the garden room and loft conversion as a fallback position.

I am aware that the appeal site is adjacent to Denham Village Conservation Area (DVCA). Paragraph 219 of the Framework states that proposals that preserve those elements of the setting that make a positive contribution to, or which better reveal the significance of such heritage assets should be treated favourably. The special character of the DVCA as a whole is derived from its assortment of buildings of different dates, scale, styles and materials and its green spaces including fields alongside the [name]. Given the appeal site’s location beyond the boundary of the DVCA and the extent and nature of the development, I find that the development would have a neutral impact on the setting of the DVCA. I note that the Council raised no objection in this regard either. Consequently, the lack of harm to the setting of the DVCA is a neutral consideration in this appeal.

I have found that the proposal would be inappropriate development in the Green Belt contrary to Policies GB1 and GB10 of the SBLP. As such, the Framework 3 Application Ref PL/25/1253/SA - Certificate of lawfulness for proposed roof alterations to dwelling and construction of outbuilding within rear garden. 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.

Other considerations in this case exist in the form of the appellant’s garden room and loft conversion fallback position, which, if carried out would result in a cluster of separate buildings which would lead to a significant loss of openness. The likelihood of the appellant implementing this development if the appeal scheme is dismissed is a significant positive consideration that in this case clearly outweighs the harm that I have identified. I therefore conclude that these other considerations represent the very special circumstances necessary to justify the development and indicate that a decision should be made other than in accordance with the development plan. I shall therefore allow the appeal.

In the interests of certainty, I shall impose standard conditions relating to the commencement of development and requiring compliance with the approved plans.

In the interest of the character and appearance of the property I shall impose a condition requiring matching materials and in the interest of biodiversity I shall impose a condition requiring ecological enhancements. For highway safety reasons I shall impose conditions regarding access and parking. In the interest of safeguarding the privacy of neighbours I shall impose conditions prohibiting further windows at the first floor in the flank elevations of the extension and prohibiting the use of the flat roof as a balcony. Finally, as the very special circumstances are contingent on the demolition of the garage and the prevention of further buildings etc at the property, a condition is necessary to remove the garage and to withdraw the Class E permitted development rights provided by the Town & Country Planning (General Permitted Development) (England) Order 2015 (as amended).

The development hereby permitted shall begin not later than three years from the date of this decision.

The development hereby permitted shall be carried out in accordance with drawing nos: PT229PL04-1; PT229PL04-2A; PT229PL04-3; PT229PL04-4; PT229PL04-5 and PT229PL04-6A.

The materials to be used in the construction of the external surfaces of the development hereby permitted shall match those of the existing building.

No further windows shall be inserted at or above first floor level in the flank elevation(s) of the two storey extension hereby permitted.

The roof area of the single storey extension hereby permitted shall not be used as a balcony, roof garden, sitting out area or similar amenity area without the grant of further specific permission from the Local Planning Authority.

Prior to the commencement of development above ground level, details of ecological enhancements including one integrated bat box and one swift box, shall have been submitted to, and approved in writing by the Local Planning Authority. The development shall proceed in accordance with the ecological enhancements, which shall have been installed prior to the first occupation of the development and retained thereafter unless otherwise agreed in writing by the Local Planning Authority.

Notwithstanding the provisions of Article 3(1) of the Town & Country Planning (General Permitted Development) (England) Order 2015 (or any Order revoking or re-enacting that Order) no development falling within Class E of Part 1 of Schedule 2 to the said Order shall be erected, constructed, or placed within the application site unless planning permission is first granted by the Local Planning Authority.

No development shall take place until the detached garage outbuilding on site at the time of the commencement of the development hereby permitted has been demolished in its entirety. All materials resulting from the demolition of the outbuilding shall be removed from the site by the substantial completion or occupation of the development hereby permitted, whichever is the sooner.

No other part of the development shall be occupied until the means of access has been provided in general accordance with the approved planning drawing and constructed to the appropriate Buckinghamshire Council access standards.

The scheme for parking, garaging and manoeuvring indicated on the submitted plans shall be laid out prior to the initial commencement of the development hereby permitted and that area shall not thereafter be used for any other purpose. End of Schedule