Part single part two storey rear extension, raised terrace and steps, hardstanding and alterations to fenestration

Appeal Decision Site visit made on 1 June 2026 by Laura Cuthbert BA(Hons) MSc MRTPI an Inspector appointed by the Secretary of State Decision date: 23 June 2026 Appeal Ref: 6003032 14 Priory Way, Datchet, Slough SL3 9JQ • The appeal is made under section 78 of the Town and Country Planning Act 1990 (as amended) against a refusal to grant planning permission. • The appeal is made by Ms M Parmenter against the decision of Royal Borough of Windsor and Maidenhead. • The application Ref is 25/01843/FULL. • The development proposed is Part single part two storey rear extension, raised terrace and steps, hardstanding and alterations to fenestration. Decision 1. The appeal is dismissed. Preliminary Matter 2. The description in the banner heading above has been taken from the decision notice, as this revised description was agreed between the parties during the application process and formed the basis upon which the application was determined. However, I note the appellant's contention that the revised description was only agreed in order to avoid delaying the progression of the application. The appellant has explained that the terrace is not raised. Rather, it would be at the same level as the finished floor level of the house, with a sunken terrace effect arising from the surrounding grassed garden area being at a slightly higher level, as shown on the proposed section drawings1. I have therefore determined the appeal on that basis. Main Issues 3. The main issues are: • the effect on the character and appearance of the area, having particular regard to the effect on the Datchet Conservation Area as a designated heritage asset through development in it and the non-designated heritage asset known as 14 Priory Way; • whether the proposal would comply with local and national planning policy which seeks to steer new development away from areas at the highest risk of flooding; and • the effect of the proposed development on trees. 1Dwg Nos. 400-00 and 400-01. Appeal Decision 6003032 2 Reasons Character and Appearance 4. The appeal site relates to a detached dwelling, finished in render, situated at the end of Priory Way, a private road running off Slough Road which leads towards the school at the end of the road. Priory Way is characterised predominantly by detached dwellings set within relatively spacious plots, interspersed with two small groups of more modern three-storey terraced properties. The street derives much of its character from the informal arrangement of development, the verdant tree- lined environment, and the variety of architectural forms, scales and roofscapes. Although there is a varied appearance to the built environment, the area nonetheless displays a cohesive low-density residential character. The existing built form of 14 Priory Way reflects the evolutionary character of Priory Way, where traditional and later infill development coexist within the area. 5. The site also lies within the Datchet Conservation Area (CA). The CA Statement for Datchet (March 1995) explains that Datchet lies on the east bank of the River Thames and that its historic form has been shaped by transport routes, including the road, rail and river networks. The CA contains a varied range of architectural styles and periods of development, including 15th century timber-framed buildings, 18th century red brick buildings, 19th century decorative brick buildings and 20th century infill development. This diversity is further reinforced by the range of plot sizes and dwelling types, from modest terraced Victorian properties to larger detached dwellings occupying wide fronted plots. This description aligns with my observations during the site visit. Consequently, the significance of the CA, for the purposes of this appeal, derives from its combined topographical, historical and architectural interest. 6. The Council states that 14 Priory Way, also known as Priory Cottage, dates from the mid-19th century and was purpose-built as an ancillary stable and coachman’s lodge associated with a wider development of which Mordenholt and Ormonde House formed part. The property has also historically been known as Mordenholt Cottage and previously as The White House. 7. Taking the above into account, I consider that the character and architectural built form of 14 Priory Way contribute positively towards the significance of the CA, reinforcing a number of the characteristics identified above that contribute to its significance. In particular, the dwelling’s age, form, proportions and varied built composition reflect the layered and evolutionary development of the area and contribute to the varied architectural character that defines this part of the CA. 8. Regardless of whether the dwelling should be regarded as a non-designated heritage asset, a matter which I return to later in my decision, I find that the building nevertheless contributes positively to the character and appearance of the area. In particular, the angled projection and varied rear form add to the dwelling’s distinctive appearance and architectural interest, notwithstanding the alterations that have occurred over time. 9. The proposed development, by virtue of its design and scale, would result in an over-dominant extension to the original building. Whilst certain elements of the proposal, including the raised terrace, would not in themselves appear harmful, the proposed extensions, most notably the substantial two-storey rear addition, but also in combination with the single storey extension, would represent an overly Appeal Decision 6003032 3 dominant and disproportionate form of development. The proposal would significantly increase the bulk, scale and massing of the dwelling and would fail to appear subordinate to the original building. As a result, the development would appear visually intrusive and would fail to respect the character and proportions of the host property, contrary to the advice in the Borough Wide Design Guide (Design Guide) (adopted 2020). 10. Having regard to the scale, siting and cumulative extent of the proposed additions, it would be a disproportionate enlargement and incongruous development, which would fail to reflect or enhance local patterns of development and neighbouring buildings. Consequently, it would be harmful to the character and appearance of the area and would undermine the positive contribution that the appeal site makes towards the significance of the CA as a designated heritage asset. 11. The appellant places significant weight on the fallback position established through the approved Certificate of Lawfulness application2, particularly in relation to the removal of the existing angled wall feature to the rear. However, a Certificate of Lawfulness confirms only that certain works would be lawful and does not amount to an assessment of the acceptability of those works in design or heritage terms. Moreover, whilst I have not been provided with exact details of what was approved under the Certificate of Lawfulness, it appears that the current proposal extends substantially beyond the scope of that fallback position. Consequently, the fallback position attracts only limited weight in these circumstances. 12. I have also considered the appellant’s assertion that the proposal has been carefully designed to appear subservient through the inclusion of a link element and through reflecting the roof form and detailing of the existing dwelling. Whilst these measures would soften some visual impacts, they would not overcome my fundamental concerns regarding the cumulative scale and bulk of the additions. The proposed two-storey rear extension would represent a substantial enlargement that would fail to be subordinate to the host dwelling and would appear as a dominant addition. 13. The development would be located to the rear of the site and would have limited visibility from the public realm. However, this does not diminish its effect on the character and appearance of the site or the CA, the significance of which derives not only from public views but also from the collective architectural character and evolution of the built environment. The proposal would erode that character through the introduction of an overly large and visually intrusive form of development that would fail to preserve or enhance the character or appearance of the CA. 14. I have carefully considered the evidence regarding whether the appeal property should be regarded as a Non-Designated Heritage Asset. Whilst it is recognised that local planning authorities may identify such assets during the determination of applications, there is no substantive evidence before me to demonstrate that the appeal site has been formally identified as such through any adopted policy or supporting document. In particular, the appellants have advised that the Datchet Neighbourhood Plan (May 2023) includes a comprehensive list of Non-Designated Heritage Assets and the appeal site is not included within this list. Consequently, 2 Application Ref. 24/00866 Appeal Decision 6003032 4 on the basis of the available evidence before me, I conclude that the appeal property cannot reasonably be regarded as a Non-Designated Heritage Asset. 15. However, this does not diminish the importance of the site's contribution to the character and appearance of the surrounding area, including the CA. The proposal would nonetheless result in harm to the character and appearance of the area, for the reasons set out above. 16. The harm that I have found to the significance of the CA would be localised. Accordingly, the harm would be less than substantial. Nevertheless, I afford considerable importance and weight to that harm. The National Planning Policy Framework 2024 (the Framework) also requires that great weight should be given to heritage assets’ conservation. As required by paragraph 215 of the Framework, this harm must be weighed against the public benefits of the proposed development. 17. I recognise that the proposal would assist in the preservation of a heritage asset as well as the maintenance of its long-term viable use. In addition, there would be some economic benefits associated with the purchase of materials and the construction of the development. Taking all the above into consideration, I am of the view that taken together, the public benefits would not outweigh the harm I have found to the heritage assets. 18. Accordingly, I conclude that the proposal would harm the character and appearance of the area and would cause less than substantial harm to the significance of the Datchet CA as a designated heritage asset, through development in it. It would conflict with Policies QP3 and HE1 of the Borough Local Plan 2013-2033 (the Local Plan) (adopted 2022), the objectives of the Design Guide, and the objectives of Sections 12 and 16 of the Framework, which together seek to secure high quality design and requires great weight to be given to heritage assets’ conservation. The historic environment should be conserved and enhanced in a manner appropriate to its significance, and development should preserve or enhance local character and heritage significance. Flooding 19. The appeal site lies wholly within Flood Zone 2 and partly within Flood Zone 3, affecting the western part of the site. Given that the proposal relates to extensions to an existing dwelling, the development would constitute minor development for the purposes of national planning policy relating to flood risk. 20. The Council’s concerns relate primarily to the lack of sufficient information originally submitted to demonstrate that the proposal would not be subject to an unacceptable risk of flooding. In response, the appellant has submitted a Flood Risk Assessment (FRA) as part of the appeal. 21. The FRA identifies the site as being at low residual risk from groundwater and reservoir flooding and finds no substantive evidence of significant flood risk arising from other sources. Whilst finished floor levels could not reasonably be raised above the predicted flood level, the proposal would maintain floor levels no lower than existing and would incorporate flood resilience and mitigation measures based on a ‘water exclusion’ strategy. The FRA further confirms that existing access and egress arrangements would remain unchanged and that future occupiers would be able to register for relevant flood warning systems. Appeal Decision 6003032 5 22. Having regard to the scale and nature of the proposal as extensions to an existing dwelling, I am satisfied that the mitigation measures identified within the FRA would provide an appropriate level of flood resilience for the lifetime of the development. I acknowledge that some residual flood risk would remain, particularly given that finished floor levels could not reasonably be raised above predicted flood levels. However, the development would maintain the existing residential use, would not materially increase the vulnerability of the site, and would incorporate measures intended to reduce potential flood impacts. Therefore, any residual risk associated with the proposal could be safely managed. Moreover, there is no persuasive evidence before me that the proposal would increase flood risk elsewhere or materially worsen existing circumstances for future occupiers. 23. Consequently, I conclude that the proposal would accord with Policy NR1 of the Local Plan, which sets out that within designated Flood Zones 2 and 3, development proposals will only be supported where an appropriate flood risk assessment has been carried out and it has been demonstrated that development is located and designed to ensure that flood risk from all sources of flooding is acceptable in planning terms. It would also be consistent with the flood risk objectives of the Framework, notably those set out in paragraph 181. Trees 24. The garden of the appeal site has a number of mature trees within it, which contribute to the local character of the area. These consist of 9 individual trees, and a group of Cedar trees. The Council’s concerns relate primarily to the proximity of the proposed extension to the trees in close proximity to the development, and the perceived lack of supporting arboricultural information at application stage. To address this matter, a Tree Survey and Arboricultural Impact Assessment (AIA) has been submitted with the appeal. 3 25. The closest trees would be an Ash tree (identified as T3 within the AIA) and a Yew tree (identified as T2 within the AIA), both categorised as BS 5837 Category C trees. The proposed extension, notably the two-storey element, would be approximately 7.23 metres from the Ash tree and 5.1 metres from the Yew tree. The AIA confirms that the proposed extension itself would be situated outside the Root Protection Areas (RPA’s) of all the trees and therefore these trees would pose no below-ground constraints on the proposed extension itself. The AIA also confirms that no trees would be removed as part of the proposal, and that the proposed building works could progress safely without the need for any pruning. I have no substantive evidence before me to come to a different conclusion. 26. The AIA recognises that there would be a small encroachment into the RPAs of a Spruce Tree (T1 in the AIA) (6.2% encroachment), the Yew Tree (T2) (8.8% encroachment) and the Ash Tree (T3) (1% encroachment) from the new sunken terrace. However, the report explains that this level of encroachment falls within recognised tolerances and would not adversely affect the health, stability, or longevity of the trees. Given the distance between these trees and the location of the proposed retaining wall, no significant roots (over 25mm in diameter) would be affected. I also note the report’s findings that Tree T3 is already affected by ash dieback and is likely to require removal in the foreseeable future irrespective of the 3 Prepared by GHA Trees Arboricultural Consultancy, dated 8 December 2025 Appeal Decision 6003032 6 proposed development. Again, I have no substantive evidence to come to a different conclusion. 27. Drawing the above matters together, I am satisfied that the appellant has now demonstrated that the proposal would not result in harm to the retained trees. Subject to the use of appropriate tree protection measures during construction, which, had I been minded to allow the appeal, would have been secured by a suitably worded planning condition, the development would safeguard the health and longevity of those trees. 28. Accordingly, for the reasons set out above, I find that the proposal would comply with the requirements of Policy NR3 of the Local Plan in respect of trees, which requires development proposals to consider the impact of development on existing trees and to protect and retain trees, including those that make a contribution to local character and distinctiveness. Other Matters 29. I note the criticisms made by the appellant in relation to the Council’s reasons for refusal concerning trees and flood risk, including the suggestion that these matters were unsupported by formal evidence or specialist consultation and had not been raised in connection with earlier applications at the site. Whilst I appreciate the appellant’s frustrations in this regard, each application and appeal must be determined on its own merits and on the basis of the information available at the time the decision is made. The fact that concerns may not previously have been raised does not preclude the Council, from considering such matters where they are relevant to the assessment of the proposal before them. 30. I also acknowledge the appellant’s concerns regarding the Council’s assessment of the appeal property as a non-designated heritage asset, including the allegation that planning policy has been applied inconsistently through the absence of any formal identification of the building within the Neighbourhood Plan or other local heritage documentation. However, the absence of formal designation does not prevent decision-makers from considering whether a building nevertheless contributes positively to the character and appearance of a CA. Ultimately, I have reached my own conclusions on these matters based on the evidence before me and my observations during the site visit. 31. I further note the absence of objection from the Parish Council. However, this does not outweigh my concerns regarding the effect of the development on the character and appearance of the site and the wider CA. Conclusion 32. The appeal scheme would conflict with the development plan. There are no material considerations, including the approach of the Framework, worthy of sufficient weight, that would indicate a decision other than in accordance therewith. The appeal is therefore dismissed. Laura Cuthbert INSPECTOR