Proposed development is mansard roof to form loft conversion

Appeal Decision Site visit made on 9 September 2025 by P B Jarvis DipTP MRTPI an Inspector appointed by the Secretary of State Decision date: 26 September 2025 Appeal Ref: APP/B1930/D/25/3368569 342 London Road, St Albans AL1 1EA • The appeal is made under section 78 of the Town and Country Planning Act 1990 against a refusal to grant planning permission. • The appeal is made by Mr and Mrs Arain against the decision of St Albans City and District Council. • The application Ref. is 5/24/0946. • The proposed development is mansard roof to form loft conversion. Decision 1. The appeal is allowed and planning permission is granted for mansard roof to form loft conversion at 342 London Road, St Albans AL1 1EA in accordance with the terms of application ref: 5/24/0946 and subject to the following conditions: 1) The development hereby permitted shall be begun within three years of the date of this decision. 2) The development hereby permitted shall be carried out in accordance with the following approved plans: 1:1250 site location plan, drawing number 100 (block plan), drawing number drawing number 201 (existing loft room), drawing number 220 (existing and proposed roof), drawing number 301 (existing and proposed elevations and floor plans). 3) The materials to be used in the construction of the external surfaces of the development hereby permitted shall match those used on the existing building. Applications for Costs 2. An application for costs was made by Mr and Mrs Arain against St Albans City and District Council. An application for partial costs was also made by St Albans City and District Council against Mr and Mrs Arain. These applications are the subject of a separate decision. Main Issue 3. The main issue is whether the proposal would be inappropriate development in the Green Belt having regard to relevant development plan policy and the National Planning policy Framework (the Framework). Appeal Decision APP/B1930/D/25/3368569 2 Reasons 4. The Framework states at paragraph 154 that development in the Green Belt is inappropriate unless one of a number of listed exceptions apply. These include at (c) 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. However, neither the Framework nor the accompanying Planning Policy Guidance (PPG) define what is to be considered as a ‘disproportionate addition’. 5. Policy 1 of the St Albans Local Plan (1994) (SALP) sets out the development types that may be permitted in the Green Belt including where there are ‘very special circumstances’ but its wording is not wholly consistent with the Framework and it makes no reference to the extension or alteration of a building. SALP Policy 13 relates to the extension or replacement of dwellings in the Green Belt but the wording of the section relating to extensions is also not wholly consistent with Framework paragraph 154c, using the phrases “significantly larger” or “different in character” rather than disproportionate additions. In accordance with Framework paragraph 232, this reduces the weight that can be given to the above policies. 6. However, the Council’s Residential Extensions and Replacement Dwellings in the Green Belt Supplementary Planning Guidance (2004) (SPG) provides some supporting guidance to Policy 13. Whilst it also predates the Framework, it does note that relevant national guidance had been updated since the adoption of the local plan to include the use of the phrase ‘disproportionate additions’. In this context, it sets out some guidance regarding the size of extensions that may be allowable, though confirms that the figures provided are guidelines with some flexibility in application having regard to how specific proposals perform in respect of a number of criteria, (i) – (viii). 7. In respect of the allowable size of extensions, part (i) a) of the SPG relates to side and rear extensions. Table 1 provides a range of indicators depending on how well individual proposals perform against the remaining criteria and this then determines the size of extension that will be permissible within the range as set out in Table 2. Table 2 indicates that increases in cubic content between 90 and 180 cubic metres or an increase in floorspace between 20 to 40% may usually be acceptable, subject to an overall maximum of 300 cubic metres. 8. However, part b) of this criterion relates to ‘other extensions’ and given that the appeal proposal would involve alterations only to the roof of the dwelling, this would seem to be the more relevant part of the guidance. It does not include any size ranges or limits but states that “the size of extensions permitted will generally be considerably smaller than with side and rear extensions” and confirms that proposals should also be assessed against all the remaining criteria. Whilst there is some dispute regarding the exact figures, the appeal proposal would add between 37-38 cubic metres volume and 15-18 square metres in floor area which, in my view, can be considered to be considerably smaller than the sizes allowable for side and rear extensions and thus criteria (i)b) is satisfied. 9. However, criteria (ii) of the SPG indicates that the cumulative impact of any previous and proposed extensions to the dwelling will also be assessed. Again, the figures are not agreed with the appellant suggesting that the original floorspace is some 40 square metres greater than that used by the Council whose figures suggest an overall increase of 185 cubic metres and a 118% increase in Appeal Decision APP/B1930/D/25/3368569 3 floorspace. The SPG is not entirely clear what these figures should be assessed against, but if Table 2 is to be used, footnote * states that whichever is the greater of the two ranges will be regarded as the top of the range. As such the cubic content increase would only be marginally above it. Applying the guidelines flexibly, even on the Council’s figures, this would be acceptable. 10. Criteria (iii) sets out the type of extensions that may be acceptable, noting that roof extensions which significantly raise the eaves or increase the ridge or bulk of the roof will normally be resisted. The proposal would add bulk to the roof but not significantly. Criteria (iv) states that the position of extensions in relation to public viewpoints will be a material factor and the appeal site and the proposed mansard roof would be visible within the street scene. However, given that the new roof would not add significant bulk and would be seen within the context of the row of detached dwellings within which it sits, screened to an extent by mature trees from the main road, its visibility would not be a detracting factor. The proposal performs well against both of these criteria. 11. Criteria (vii) relates to Policy 72 constraints which should be carefully addressed. The proposed mansard roof would introduce a slightly different roof form compared to the predominant hipped roofs, but due to its design and relatively small crown roof, would relate well to the scale and character of the street and would be compatible with the original building. It would not seriously diminish the space around the building nor have an adverse effect on adjoining properties. Overall, the policy constraints would be satisfied. 12. Criteria (v) relating to extensions in gaps between dwellings, (vii) landscaping and tree preservation and (viii) conservation areas and listed buildings are not relevant. 13. Taking all the above into account, I find that the proposal would not result in a significantly larger building on the appeal site nor a building of different character. Overall, it would not result in disproportionate additions over and above the size of the original building. It would thus satisfy Framework paragraph 154(c) and as such it would not be inappropriate development in the Green Belt. As such it is not necessary to consider the impact on Green Belt openness any further, nor is it necessary for very special circumstances to be demonstrated. 14. The proposal would comply with SALP policies 1 and 13 and the SPG guidance. In addition, for the reasons set out above, there would be no conflict with SALP policies 69 and 72 which, amongst other things, seek to ensure development of a high quality design that in the case of residential extensions seek to ensure that it relates to the scale and character of an area, is compatible with the original building, does not seriously diminish the space around it nor result in adverse impacts on neighbouring properties. Conditions 15. The Council has suggested a number of conditions which I have reviewed in the light of Framework paragraphs 56 and 57. A condition to refer to the approved plans is necessary in the interests of clarity and proper planning. A condition to require matching materials is also necessary in the interests of visual amenity. The Council has also suggested a condition to prevent the use of the flat roof to the front of the balcony as an amenity area / roof garden. However, I see no need for such a condition given the very small area involved and that access to it would, in Appeal Decision APP/B1930/D/25/3368569 4 any event, be prevented by the railings to be attached in front of the door. A condition relating to biodiversity net gain is also unnecessary given that the type of development proposed is exempt from such requirements. Conclusion 16. I therefore conclude that this appeal should be allowed. P B Jarvis INSPECTOR