What is a Heritage Impact Assessment and when is it required?
For all applications relating to a heritage asset, (designated or non-designated) or for works within their setting, a Heritage Impact Assessment is required. When submitting an application, the National Planning Policy Framework (NPPF) at policy HE5, parts 1-3 requires applicants to assess both the significance of any assets affected by the development proposals, and the effects of development proposals on the significance of those heritage assets. Whilst the detail should be proportionate, that proportionality is to the effect on a heritage asset’s significance rather than the scale of the development proposal
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HE5: Assessing effects on heritage assets
Development proposals affecting heritage assets should be accompanied by an assessment of the significance of the assets affected (including any contribution made by their setting) and of the potential effect of the proposal on their significance. The level of detail should be proportionate to the assets’ importance and no more than is necessary to understand the potential effect of the proposal on their significance. The relevant historic environment record should be referred to in making this assessment, and appropriate expertise employed where necessary.
Assessments of the potential effects of development proposals on the significance of heritage assets (including through effects on their setting) should identify whether proposals would be likely to: a. Have a positive effect, which is where the significance of a heritage asset would be enhanced, or better revealed; or b. Have no effect on the significance of a heritage asset; or c. Result in harm to the significance of a heritage asset, either from work affecting the asset itself or from development within its setting. The degree of harm should be identified: substantial harm would occur where the development proposal would seriously affect a key element of the asset’s significance; or d. Cause the total loss of the significance of a heritage asset.
In making this assessment it is the effect on a heritage asset’s significance rather than the scale of the development which should be considered.
Decision-makers should be satisfied that assessments accurately reflect the effects on heritage assets caused by development proposals.
Where a development proposal involves, or has the potential to involve, a heritage asset with archaeological interest, an appropriate desk-based assessment should be undertaken and, where necessary, a field evaluation. These should be used to help understand the asset’s significance and the potential effect of the proposal on this, which should inform the design, mitigation and implementation of the development.
National Planning Policy Framework, August 2026
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Part 1 of HE5 sets out that appropriate expertise should be employed where necessary. The following extract is taken from Historic England Advice Note 12 (HEAN12) on Statements of Heritage Significance:
“Where the significance is not obvious, appropriate expertise would need to be used, as the NPPF points out (paragraph 189)*. Analysis would generally be undertaken by a suitably qualified specialist, expert in an appropriate branch of conservation, architectural history, garden history and/or archaeology, or, in more complex circumstances, group of specialists, who can describe significance in a way which is acceptable to the local planning authority and which therefore assists a successful application. For further information, see Managing Significance in Decision-Taking in the Historic Environment: Historic Environment Good Practice Advice in Planning 2, which lists established registers that can be used to identify appropriately qualified specialists or organisations, depending on the nature of the project.”
Statements of Heritage Significance: Analysing Significance in Heritage Assets
(*The requirements of para 189 of the previous NPPF are reflected in the requirements of Policy HE5 of the new NPPF 2026).
Appropriately qualified specialists also include the use of a Structural Engineer identified within the Conservation Accredited Register of Engineers (CARE).
The guidance also advises that the understanding of significance should generally come before the design of proposals. It states ‘Taking decisions about a proposal out of sequence can lead to abortive work, raised costs and delays. Assessing significance before a proposal is planned can lead to better outcomes for the applicant by influencing the design by mitigating harmful impacts on significance, enhancing significance where possible, and thereby showing how any remaining harm is justified.’
Under part 5 of HE5, where a development proposal involves, or has the potential to involve, a heritage asset with archaeological interest – including archaeological interest in standing building. There is a common misconception that archaeology relates to below ground remains only. Buildings are also archaeology as they hold evidence of past human activity and are a primary source of evidence about the substance and evolution of places and the people and cultures that made them. Archaeological recording of standing buildings is a standard practice in order to help to understand significance, particularly where development is likely to impact upon a heritage asset through alteration or demolition, and to investigate the most appropriate routes for mitigation of harm where this can be achieved. Further information on Archaeological Interpretative Surveys of standing buildings is available on the East Sussex County Council website (ESCC) .
What should you include within a Heritage Impact Assessment (HIA)?
A Heritage Impact Assessment must show firstly that you understand the significance of the heritage asset(s) affected, and secondly identify any effects on that significance – whether they are positive or negative. You should also use the HIA to demonstrate how your understanding of the significance of the heritage asset has been used to inform the changes proposed in order to provide benefits and/or avoid harm, or where harm cannot be avoided, how any harm has been minimised. The assessment should be proportionate to the works proposed, but the information required will depend on the asset’s significance rather than the scale of development proposed.
In order to do this, the following steps should be followed:
- Analyse and understand the special interest (significance) of the heritage asset through its history, form and materials (archaeological, architectural, artistic and historic interest), and the contribution made by setting where relevant.
- Using the understanding of its significance, show how the proposed changes to the heritage asset conserve the heritage asset and identify the resulting potential effects using the terminology in policy HE5(2).
- Show what alternatives have been considered to avoid (or if that is not possible, minimise harm) on special interest and how the proposals take opportunities to better reveal or enhance the significance of the heritage asset.
Advice has been published by Historic England in Advice Note 12: Statements of Heritage Significance – Analysing Significance in Heritage Assets.
Further advice is also available in this section through the tabs on the right-hand side of the page (to be updated).
The Historic Environmental Record (HER)
In addition, the NPPF requires the relevant Historic Environment Record (HER) to be referred to in making the assessment of significance. Any correspondence with the HER should fomr an appendix to your Heritage Impact Assessment. The absence of information on the HER does not signify that there is no special interest or significance to a heritage asset.