What Is a Heritage Impact Assessment?

A Heritage Impact Assessment only makes sense once two things already exist: a Statement of Heritage Significance for the asset, and a confirmed design. It measures the second against the first. Without a significance baseline, an impact assessment has nothing to measure impact against, and reads as an unsupported assertion rather than an evidenced conclusion.

What does an HIA cover?

• A summary of the asset's established significance, drawn directly from the Statement of Heritage Significance.
• A description of the proposed works, in enough detail to assess against that significance.
• An assessment of effect — whether the proposal has a positive effect, no effect, or causes harm to significance, and to what degree.
• Where harm is identified, an explanation of why it is outweighed by the public benefits of the proposal, and what has been done to minimise it.
• Any mitigation measures, further research or recording proposed as part of the works.

How is harm categorised under current policy?

Under the National Planning Policy Framework published in August 2026, the familiar phrase "less than substantial harm" is no longer used as a policy test. Effects on a designated heritage asset are instead assessed on a scale from positive effect or no effect, through to harm, and, in the most serious cases, total loss of significance. [GPS TO VERIFY: confirm the exact current wording of the harm scale in the August 2026 NPPF before this guide is published, and cite the specific policy reference.] Whatever the current terminology, the underlying exercise is the same: any harm identified has to be weighed against the public benefits the proposal delivers, and the weighing has to be shown in the document, not just asserted.

Do retrofit and energy efficiency works count differently?

Where the proposed works involve energy efficiency or low-carbon heating measures, or bring a vacant or underused listed building back into use, current NPPF heritage policy names these specifically as public benefits to be weighed in the balance against any harm identified — see our retrofit guide for what this means in practice.

Who prepares one, and when?

An HIA is normally required alongside a Listed Building Consent application for anything beyond minor works, and is standard practice for any application likely to affect the setting of a heritage asset as well as the asset itself. It should be prepared once the design is fixed enough to assess, but early enough that the findings can still influence detail design if a problem is identified — not as a final tick-box exercise once drawings are submitted.

What if the assessment finds harm — does that mean refusal?

Not necessarily. Finding harm is not the same as recommending refusal; it is the starting point for the balancing exercise the NPPF requires. A well-evidenced HIA that identifies harm honestly, explains why it is the minimum necessary to achieve the proposal's aims, and sets out the public benefits that weigh against it, gives a case officer something they can actually assess and potentially support. An HIA that glosses over or understates harm to make the numbers look better tends to be spotted by an experienced conservation officer, and damages the credibility of the rest of the application.

How does an HIA differ from a Design and Access Statement?

A Design and Access Statement (DAS) explains the design process and access arrangements for a wider range of applications, and is a general planning requirement, not a heritage-specific one. An HIA is heritage-specific and goes into far more depth on significance and harm than a DAS typically would. The two are often submitted alongside each other, with the DAS able to reference the HIA's findings rather than repeating the heritage analysis in full.

Does an HIA need to consider the setting of the building, not just the building itself?

Yes, where setting is relevant. A proposal does not have to touch a listed building's fabric to affect its significance — a new structure nearby, a change to its immediate surroundings, or the loss of an open aspect the building was designed to relate to, can all affect how the asset is experienced and understood. Historic England's Good Practice Advice Note 3 sets out a staged approach to assessing setting: identifying the heritage assets potentially affected, assessing the contribution setting makes to significance, and then assessing the effect of the proposed change. An HIA for a proposal near a heritage asset, rather than to it directly, should address this explicitly rather than assuming setting is out of scope simply because the works are off-site.