Appeal 6002662

The appeal is dismissed.

The main issue is whether in the absence of condition no.4, the development would make appropriate provision for water management and contribute to biodiversity.

Policy 31 of the Cambridge Local Plan (CLP) 2018, seeks a water sensitive approach to the design of new development. It requires compliance with 11 criteria including but not limited to, a) surface water being managed close to its source and f) any flat roof is a green or brown roof, providing it is acceptable in terms of its context in the historic environment of Cambridge. Criterion f) is clear that it does not encourage biodiverse roofs, rather it requires them where roofs are proposed to be flat.

The supporting text to Policy 31 explains that green and brown roofs are a key measure in addressing climate change and delivering sustainable development. It highlights their role in managing surface water run-off, reducing peak flow rates, improving thermal performance and contributing to biodiversity by supporting a range of plant and animal species.

The approved plans show that the extension would have an almost flat roof. In these circumstances, the provision of a flat roof without a green or brown roof covering would be at odds with the requirements of Policy 31, particularly given that there are no heritage constraints to warrant a different approach. Given the terms of that policy, condition 4 is therefore necessary to make the development acceptable in planning terms. The specification of planting, substrate depth, maintenance arrangements and restrictions on use would ensure that the roof functions effectively in terms of both water management and biodiversity. Consequently, the condition is relevant to planning and to the development, is sufficiently precise and would be enforceable. I consider that it does not go beyond what is reasonably required by the development plan.

The appellant suggests that compliance with condition 4 would lead to excessive structural loading, requiring disproportionate reinforcement works and an increase in the overall height of the extension. However, no structural calculations or technical drawings have been submitted, to demonstrate that the roof could not reasonably accommodate a biodiverse roof of the specification required by the condition. In the absence of such evidence, I am not persuaded that the requirements of the condition would be unnecessary or unreasonable.

The appellant also contends that a soakaway system would achieve comparable surface water management objectives. While sustainable drainage systems are encouraged more generally, the wording of Policy 31(f) makes it clear that green or brown roofs are the expected solution for flat roofs. In this case, there are no heritage or site-specific constraints which would justify departing from the approach set out in the policy.

Whether or not the development would be located on a previously developed footprint, Policy 31 is concerned with securing positive contributions to biodiversity, rather than simply avoiding harm. A flat roofed extension provides an opportunity to deliver such benefits, and the condition seeks to secure a modest but policy-compliant gain.

Taking all matters together, I find that condition 4 would secure compliance with Policy 31 of the CLP and reflects the development plan’s approach to flat-roofed development. It also meets the tests for conditions set out in national planning policy and guidance1. Without the condition, the development would fail to make appropriate provision for water management and biodiversity. My findings are consistent with those of the Inspector in the [address] appeal referred to by the Council2.

The appellant suggests that if the extension did not have external cladding it could be constructed under permitted development rights, which would not require a green roof. However, no specific details have been provided to demonstrate that such a scheme would meet the relevant criteria for permitted development, and there is no certificate of proposed lawful development before me. Even if it could 1 Paragraph 57 of the National Planning Policy Framework and paragraph: 003 [name]: 21a-003-20190723 of the Planning Practice Guidance. 2 be considered as a fallback position, there is insufficient evidence to show that it would have a realistic prospect of being implemented. Given that the appellant has pursued planning permission for the proposed scheme, I attach only limited weight to the suggested fallback position.

The development with condition no.4 removed, would conflict with the development plan. The limited weight attached to the suggested fallback position would be insufficient to outweigh the harm in respect of water management and biodiversity. Accordingly, the appeal is dismissed.