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Mitigating Standard Design Features to be Considered at Stage 1 Appropriate Assessment?

The Court of Justice of the European Union (CJEU) issued its decision in a recent case, Eco Advocacy CLG v An Bord Pleanála and Keegan Land Holdings Limited ([2021] IEHC 265), on the question of whether standard design measures, which have mitigating effects, can be considered at the screening stage of an Appropriate Assessment.


In 2021, Mr Justice Humphreys presided over a High Court judicial review relating to a proposed development in Trim, Co. Meath, which was to consist of 320 dwellings. The proposed development was subject to a screening, a Stage 1 Appropriate Assessment. This is an environmental assessment required to comply with the Habitats Directive.

In this instance, the proposed development was in the vicinity of a special area of conservation and special protection area, namely the River Boyne and River Blackwater SAC and River Boyne and River Blackwater SPA. As a result, the project required a Stage 1 Appropriate Assessment. If the potential for significant effects cannot be excluded at the screening stage for the development, alone or in combination with other plans and projects, a Stage 2 Appropriate Assessment must be carried out. This is a relatively light trigger and must be based on the precautionary principle.

By a decision in October 2020, An Bord Pleanála (the Board) authorised the proposed development and issued the requested planning permission, taking the view that a Stage 2 Appropriate Assessment was not required.

The design of the proposed development incorporated a surface water run-off from the development to be collected below ground in storage tanks and be treated before out-falling to a stream around 100 metres south of the development. This would result in reducing the potential for effects on the protected sites. The question was whether this was a mitigation measure which could not be taken into account in a Stage 1 Assessment and could only be considered in a Stage 2 Appropriate Assessment.

This question arose because since the ruling of the CJEU in case C-323/17 People Over Wind and Peter Sweetman v Coillte, it has been understood that mitigation measures cannot be taken into account at Stage 1 of an Appropriate Assessment.

Referral to the CJEU

In this case in the High Court, Mr Justice Humphreys stated:

“the real question here is whether the surface water drainage system constitutes a mitigation measure or not to be regarded as such because it is simply a standard feature of the design that has nothing to do with the nearby European sites.”

Accordingly, Mr Justice Humphreys referred a question to the CJEU to provide clarity on this issue. Broadly, the Court asked whether a competent authority is entitled to take account of project features that:

  • Are not intended to reduce harmful effects on a European site even if they have that effect, and
  • Would have been incorporated into the design as standard features

Read here for further details of the High Court matter.

The CJEU issued its decision on this issue on 15 June 2023 and stated as follows:

“….in order to determine whether it is necessary to carry out an appropriate assessment of the implications of a plan or project for a site, account may be taken of the features of that plan or project which involve the removal of contaminants and which therefore may have the effect of reducing the harmful effects of the plan or project on that site, where those features have been incorporated into that plan or project as standard features, inherent in such a plan or project, irrespective of any effect on the site”


This is good news for developers. The CJEU has provided clarity on this point and concluded that standard design features, which have mitigating effects on sites protected under the Habitats Directive, and which have been incorporated into the design of the project can be considered at the screening stage of an Appropriate Assessment. It also confirms that this does not automatically require a Stage 2 Appropriate Assessment. It is important to remember however that the assessment of any such design features will be based on objective criteria and developments which feature mitigating measures at the screening stage of an Appropriate Assessment as part of the design of the development will likely be scrutinised by the Board and the Court.

To note: This decision follows the Opinion of the Advocate General on the matter which was issued in January 2023.

For more information, please contact a member of our Planning & Environment team.

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

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