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The design envelope approach

Wind turbine technology is developing rapidly in Ireland. Developers normally seek flexibility in their permitted designs to allow them to procure the most cost-effective and efficient technology available at the point of construction. This can be years after the designs for the planning application were prepared. The design envelope approach to planning applications is based on a range of potential designs. This process is also commonly known as the “Rochdale envelope” and may include the precise location of the turbines; the cable route; the foundation type; the turbine heights and blade lengths within an “envelope”.

A 2020 European Commission guidance document on wind energy developments and EU nature legislation advised that the “Rochdale envelope” is a proven and acceptable approach to granting permission where there is uncertainty in the design. This is provided the environmental impact assessment (EIA) and appropriate assessment (AA) evaluates the worst-case design possible.

Proposed wind farm at Derryadd

Peter Sweetman brought a case to challenge An Bord Pleanála’s (the Board) decision to grant permission to Bord na Móna PowerGen Ltd to develop a windfarm on bogland in Derryadd, near Lanesborough, Co Longford in June 2020. If constructed to the maximum dimensions allowed, the turbines would have been the joint tallest structures in Ireland. The judgement noted that the turbines would stand “higher than the Gherkin Tower in London”, along with “extensive rail networks”. The planning application was lodged with the Board under the strategic infrastructure development (SID) procedure.

The applicant brought a challenge based on alleged deficiencies in the EIA and AA, including making use of infrastructure constructed without EIA or AA where such assessments would have been required by EU law. Justice Humphreys didn’t consider the need to decide those “EU law points”. He held the SID permission was unlawful on the basis that the plans and particulars were not sufficiently precise.

Inadequate design detail

Article 214 of the Planning and Development Regulations 2001 (as amended) (the PDR) require “plans and particulars of the proposed development” to be submitted with an SID application. The Board’s General Guidance Note for submitting SID applications states that material must “generally accord” with the requirements for a planning application as set out in the PDR. Mr Sweetman complained that the plans and particulars lodged showed “virtually no detail and no site-specific detail”, leaving core elements of the design of the project to the post-consent stage. The Judge accepted that this broad complaint amounted to a breach of Article 214. This was the case even though the applicant did not reference this article in his pleadings until final replying submissions were delivered.

Justice Humphreys agreed with Mr Sweetman, stating, “in particular, the turbine heights and blade lengths are expressed in terms of maxima, not the actual proposed dimensions. That is equivalent to applying for planning permission for a house on the basis that it could be anything from a one-storey bungalow to a ten-storey mansion”.

The Judge found that while the concept of “plans and particulars” is not defined by the legislation, it nonetheless requires something specifically measured. In particular, something capable of being drawn on a plan. Crucially, this cannot include a widely variable design envelope. The Judge referred to case law where modest variations between the plans submitted and the structures constructed have been allowed. However, he considered that this didn’t apply to a case where a scale is open at one end.

Justice Humphreys considered that “even the English doctrine of the Rochdale envelope is not a blanket acceptable of variable applications, and the facts in Rochdale are a world away from the facts here.” Furthermore, the concept of the design envelope has a written basis in English law in the national guidelines. It is not simply a question of assessing a project by reference to a “worst case scenario” alone, but by reference to those parameters and any flexibility they involve.

At several points in the judgment, it was mentioned that planning law is an area of growing complexity. The judge said, “to construct such a procedure out of whole cloth would be a hazardous, if not quixotic venture for a court to embark on, particularly at this stage of the evolution of planning law.”


Given that a design envelope approach is a popular method to accommodate emerging technologies without the need for alterations to the consent, this judgment is likely to have significant implications for wind turbine planning applications. It is clear that the balance between flexibility and certainty in design particulars has swung towards the latter.

Developers must give reasonably precise plans for what they intend to build in order for third party objectors and other interested people to advocate for their own concerns. This judgment raises the concern that lack of specificity in design parameters could be fatal to a carefully crafted planning application. Furthermore, it leaves open the question of to what extent the design envelope approach is lawful in the context of an EIA or AA.

Developers will need to carefully consider how to approach this issue in applications.

If you wish to discuss the impact of the Level 5 restrictions may have on your project, contact a member of our Renewable Energy team.

The content of this article is provided for information purposes only and does not constitute legal or other advice.

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