Heritage harm and mitigation

First published by LexisNexis

When considering the impact of a proposed development on the significance of a designated heritage asset, chapter 16 of the National Planning Policy Framework states that the level of harm is to be categorised as either 'substantial' or 'less than substantial'. In cases where the developer has proposed mitigation measures within their planning application, should the level of harm be determined before or after the mitigation measures have been considered by the Planning Officer?

Paragraphs 189–192 of chapter 16 of the National Planning Policy Framework (NPPF) are entitled 'Proposals affecting heritage assets' and paragraphs 193–202 'Considering potential impacts'. These paragraphs do not refer to 'mitigation measures', but it is nonetheless clear that the assessment to be undertaken by the local planning authority (LPA), as to whether the development proposal causes substantial or less than substantial harm, is to be conducted after mitigation measures have been taken into account.

Paragraph 196 states: 'Where a development proposal will lead to less than substantial harm…' (emphasis added).

Paragraph 197 states: 'The effect of an application on the significance of a non-designated heritage asset…' (emphasis added).

These extracts make it clear that it is the 'development proposal' and the 'application' that is to be considered. A development proposal/application will normally be presented to the LPA as a complete package that includes measures that avoid, minimise and mitigate heritage harm. In fact, there is an onus on the applicant to do just this.

Paragraph 6 of Historic England’s guidance ‘Managing Significance in Decision-Taking in the Historic Environment: Historic Environment Good Practice Advice in Planning: 2’ sets out a suggested structured approach to assessment by applicants. This is as follows:

• 'Understand the significance of the affected assets
• Understand the impact of the proposal on that significance
• Avoid, minimise and mitigate impact in a way that meets the objectives of the NPPF
• Look for opportunities to better reveal or enhance significance
• Justify any harmful impacts in terms of the sustainable development objective of conserving significance and the need for change
• Offset negative impacts on aspects of significance by enhancing others through recording, disseminating and archiving archaeological and historical interest of the important elements of the heritage assets affected'

Reference should also be made to Historic England’s guidance 'The Setting of Heritage Assets: Historic Environment Good Practice Advice in Planning: 3', which includes paragraphs 26–29 entitled 'Maximising enhancement and minimising harm'. Examples are given of measures that enhance, minimise and mitigate harm.

Measures that 'avoid' harm form part of the initial scheme design, for example the orientation of a block, or the distance of a block from a boundary. The Planning Practice Guidance refers to this in the following terms:

'Understanding the significance of a heritage asset and its setting from an early stage in the design process can help to inform the development of proposals which avoid or minimise harm… appraisals or investigations can identify alternative development options, for example more sensitive designs or different orientations…' (Paragraph: 008 Reference ID: 18a-008-20190723).

Measures that 'minimise' harm will be design features that form part of the overall package, such as selecting a coloured render to match that of an adjacent listed building, or an ironmongery detail that takes design clues from the listed building.

Examples of measures that 'mitigate' harm are planting screening, or asset management.

Other mitigation will be conditions on a consent such as recording, reporting and written schemes of investigation.

The entire approach to assessment of harm by the applicant is therefore one that requires 'mitigation measures' to be considered holistically. It would be bizarre if the assessment of the application to be undertaken by the LPA required it to strip out from its consideration some or all of these measures.

If the NPPF author had intended that assessment of heritage harm should not be of the application or development proposal as a whole, then this would have needed to have been made much clearer. The common sense reading of NPPF paragraphs 196 and 197 is that it is the entire development proposal that is to be considered by the LPA when assessing heritage harm.

For further guidance, see Practice Note: Heritage issues in determining planning applications.