" Development is not permitted by Class A if - ..... (f) subject to paragraph (g), the enlarged part of the dwellinghouse would have a single storey and - (i) extend beyond the rear wall of the original dwellinghouse by more than 4 metres in the case of a detached dwellinghouse, or 3 metres in the case of any other dwellinghouse, or (ii) exceed 4 metres in height."
"7 The proposed single-storey rear extension would project some 2.3 metres beyond the existing rear wall of this previously extended semi-detached house. As the proposed extension, together with the existing extension, would project some 5.1 metres to the rear of the rear main wall of the original dwelling, the overall enlargement of the house would not exceed six metres. On this basis, and because the maximum height of the new extension would be around 2.8 metres, the appellant submits that it would be permitted development. 8 There is, however, some disagreement between the parties concerning the enlarged part of the dwellinghouse. There is no dispute that the existing extension includes both two-storey and single-storey elements. As such, the council maintains that even though the additional extension now proposed would have only a single storey the enlarged part of the house would include more than a single storey, whereas the appellant contends that the enlarged part would have a single storey."
"12 Moreover, the question of whether existing extensions are part of the enlargement of a building was examined in Kensington & Chelsea Royal Borough Council v SSCLG[2015] EWHC 2458 (Admin) . It was held that the 'enlarged part of the dwellinghouse' does not include the 'original' building, but does include previous enlargements. 13 In this appeal, the proposed extension would, taken together with the existing extension, not be a single-storey enlargement to the dwellinghouse. It would not, therefore, be permitted development under the terms of Part 1 Class A.1(g)(i) of the GPDO. Furthermore, as the enlarged part of the house would exceed 4 metres in height on account of part of the existing extension having two storeys, the proposal would not be permitted development under the terms of Part 1 Class A.1 (g)(ii) of the GPDO. 14 Since the proposal would not be permitted development, it is not necessary to consider the effect on the amenity of the neighbouring occupiers in this case."
"(5) The local planning authority must notify each adjoining owner or occupier about the proposed development by serving on them a notice which - (a) describes the proposed development, including - ..... (ii) the maximum height of the enlarged part of the dwellinghouse; and (iii) the height of the eaves of the enlarged part of the dwellinghouse."
"Development is not permitted by Class B if - ..... (b) any part of the dwellinghouse would, as a result of the works, exceed the height of the highest part of the existing roof."
" ..... the roof space as enlarged, taking into account any enlargement to the original roof space, whether permitted by this Class or not."
" ..... whether the phrase 'the enlarged part of the dwelling house would have more than one storey' in paragraph A.1 (f) is referring to the dwelling house as enlarged by development, i.e. to include the original dwelling house, or whether it is referring to that part of the dwelling house permission for which is given by Class A of the GPDO."
"[29] Within paragraph A.1 (f) the draftsman has drawn a distinction between 'the enlarged part of the dwelling house' and the 'original dwelling house'. That has clearly been done with a purpose and, in my judgment, is to clarify the interpretation of the paragraph. [30] They refer to two different things. The 'enlarged part' is referring to the development permitted under the GPDO. The 'original dwelling house' is the dwelling house as defined in accordance with Article 1 of the GPDO. ‘Original' is defined in Article 1 of the GPDO: ''Original' means, in relation to a building existing on1 July 1948 , as existing on that date and, in relation to a building built on or after1 July 1948 , as so built.' [31] The Claimant's submission that 'enlarged part' incorporates the original is artificial and, in my judgment, offends the natural language used in Class A.1(f). [32] Further, when Class A is read as a whole it is clear that 'it' refers either to the subject immediately preceding, i.e. the enlarged part of the dwelling house, or back to the opening words 'development is not permitted by Class A.1 (f)'. [33] The purpose of the GPDO is to compare what is proposed with what existed prior to the proposal to ascertain whether the exceptions are engaged. That is why it is important to have a definition of the 'original' under Article 1. [34] The Claimant contends that such an approach will not catch 'piggybacking' or incremental development. I reject that submission. Article A.1(f) is dealing with the enlargement or alterations to the original dwelling house. Each step of incremental development has, therefore, to be judged against that baseline so that incremental development is caught each time it is proposed. [35] I accept the submissions of the Defendant that 'part' cannot be characterised as meaning the whole of the dwelling house as enlarged. The original dwelling house and the enlarged part of the house may combine to make a dwelling house as enlarged, but they are two separate components. That interpretation has the advantage of being both straightforward and consistent with the language used."
"[43] It follows that the 'enlarged part of the dwelling house' is referring solely to that which is the subject of permission granted under the development order. The first issue, therefore, I determine in favour of the Defendants."