Heritage Impact Assessments: Structure, Purpose and Checklist

What Is a Heritage Impact Assessment?

A Heritage Impact Assessment, often referred to as a Heritage Statement, is a report which accompanies a planning application or listed building consent application. It explains what is historically important about a building, site or area, and considers how the proposed works would affect that importance.

The central idea is significance. Before a local planning authority can make a decision, it needs to understand what is special about the heritage asset, which parts matter most, how its setting contributes to its value, and whether the proposal would preserve, enhance or harm those qualities.

An HIA is not simply a description of an old building. It is a reasoned document which links research, site inspection and an understanding of the proposed works. Its job is to show that the applicant has understood the building or place before deciding how to change it.

When Is an HIA Needed?

A Heritage Impact Assessment is normally required where a proposal would affect a heritage asset or its setting. This includes applications for listed building consent, as well as many planning applications involving listed buildings, conservation areas, scheduled monuments, registered parks and gardens, historic battlefields, archaeological remains and locally listed buildings.

It may also be needed where the application site is outside the boundary of a heritage asset but is visible from it, forms part of its historic surroundings, or affects an important view, relationship or landscape setting. A new building beside a listed church, for example, may need an HIA even though no part of the church itself is being altered.

The exact local validation requirements vary between councils. It is sensible to check the relevant council’s planning validation list at the start of a project. In practice, an HIA should be prepared early where there is any realistic possibility that heritage significance may be affected.

Why Is It Needed?

The National Planning Policy Framework requires applicants to describe the significance of heritage assets affected by a proposal, including the contribution made by their setting. The information must be proportionate to the importance of the asset and the likely impact of the proposed works.

A good assessment benefits both the applicant and the council. It identifies potential difficulties before designs are fixed, makes it easier to discuss proposals with the conservation officer, and provides a clear basis for explaining why particular repairs, alterations or materials have been chosen.

It can also avoid delay. An application supported by vague or incomplete heritage information may be made invalid, delayed while further details are requested, or refused because the authority cannot properly assess the effect of the proposal.

Who Normally Prepares an HIA?

The right person depends on the complexity of the case. A simple proposal involving a modest Grade II listed building may be dealt with by an experienced heritage contractor, conservation architect, historic-building surveyor or planning consultant with relevant expertise.

More complex cases need more specialist input. This may include a conservation-accredited architect, a heritage planning consultant, a building archaeologist, an archaeologist, an architectural historian or a specialist surveyor. Grade I and Grade II* listed buildings, scheduled monuments, substantial alterations, demolition proposals and schemes affecting several heritage assets generally require an experienced heritage professional.

The key point is not the job title but the quality of the work. The author should understand historic buildings, conservation principles, planning policy, traditional materials and the significance of the asset in question.

How Much Does an HIA Cost?

Costs vary according to the importance of the heritage asset, the complexity of the proposal, the amount of research required and the number of affected buildings or settings.

A straightforward Heritage Statement for minor works to a Grade II listed building may commonly cost around £1,000 to £2,500. A more detailed assessment involving a sensitive setting, a substantial extension, several affected heritage assets or detailed archival research may cost £3,000 to £8,000 or more.

Those figures are only broad market indications. A short report can still require careful thought, while a larger report may be relatively straightforward if the building has already been well researched. The best approach is to obtain a fixed fee based on a clear brief, site visit and outline drawings.

Part 1: Recommended HIA Structure

1. Introduction and Methodology

Begin by identifying the site, the proposed development and the heritage assets that may be affected.

State whether the site itself is listed, lies within a conservation area, contains archaeological potential, or is within the setting of a designated or non-designated heritage asset. Identify the relevant list entry, conservation area appraisal, local plan policies and any planning history that is directly relevant.

Explain how the assessment has been prepared. This should normally include a site inspection, review of the Historic Environment Record, historic mapping, listed building descriptions, local archives where appropriate, photographs and relevant Historic England guidance.

The report should also make clear that the assessment is proportionate. A small repair to a modern rear addition does not need the same level of research as major alterations to the principal rooms of a Grade II* country house.

2. Baseline Research and Description

Provide a factual account of the building, site or area. This should describe its age, form, materials, construction, plan, appearance and historical development.

For a building, this may include its original purpose, later additions, surviving historic features, changes in use and condition. For a site or setting assessment, it may include historic boundaries, views, landscape features, neighbouring buildings and the way in which the asset is experienced.

Historic map evidence is often particularly useful. It can show whether a building has been extended, whether a field pattern has survived, or whether an apparently ordinary outbuilding once formed part of a larger estate, industrial complex or farmstead.

The purpose of this section is to establish the facts before reaching conclusions about significance or impact.

3. Statement of Significance

The statement of significance is the heart of the assessment. It should explain why the asset matters, rather than merely repeating the statutory list description.

Significance may arise from archaeological interest. This includes evidence of past human activity which survives in the ground, in the structure of a building, or in buried remains.

It may arise from architectural and artistic interest. This can include the design of the building, its plan form, craftsmanship, materials, detailing, decorative features, historic joinery, roof structure, masonry or special architectural character.

It may arise from historic interest. This includes associations with people, events, former uses, social history, local identity and the way in which a building or place illustrates the development of an area.

The assessment should distinguish between parts of high, medium and low significance. A historic staircase, timber frame or principal elevation may be highly significant. A twentieth-century kitchen extension, later partition or poor-quality modern window may be of low significance. This distinction is vital because it allows change to be directed towards the least sensitive areas.

4. Assessing Setting

Setting is not simply the land immediately around a heritage asset. It is the surroundings in which the asset is experienced, where those surroundings contribute to its significance.

For some buildings, setting may be very limited. A listed terraced house may derive much of its significance from its own fabric and its relationship with the street. For a church, hall, farmstead, bridge or former industrial building, setting may extend much further and include views, approach routes, landscape, historic relationships and the wider settlement pattern.

The report should identify the particular aspects of setting that matter. This may include a view of a church tower across open land, the relationship between a hall and its parkland, the separation between a former mill and later housing, or the rhythm and scale of a conservation area street.

It should avoid making broad claims about all views being important. The question is whether a particular view or relationship genuinely contributes to the asset’s significance.

5. Description of the Proposed Development

Describe the proposed works clearly and accurately. This section should be factual before it becomes evaluative.

Identify the elements to be repaired, removed, replaced, extended or newly introduced. Explain the construction methods and materials where they are relevant to heritage impact. Include references to drawings, elevations, plans, sections, photographs and schedules of work.

For listed buildings, it is helpful to describe works room by room or elevation by elevation. For example, state whether plaster is to be repaired or removed, whether existing joinery will be retained, whether a wall will be opened up, and what will happen to historic fabric exposed during the works.

For setting assessments, explain the scale, height, massing, materials, access arrangements, landscaping, lighting and visibility of the proposal.

6. Assessment of Impact

Assess the effect of each element of the proposal against the significance identified earlier in the report.

A repair using appropriate traditional materials may preserve or enhance significance. The removal of a poor modern addition may reveal the significance of an earlier building. A new opening through a historically important wall, however, may cause harm even if it is carefully designed.

The assessment should be specific. Avoid simply saying that a proposal has “minimal impact” without explaining why. A stronger approach is to identify the affected feature, state its significance, describe the proposed change and then assess the likely effect.

The scale of effect may be described as beneficial, neutral, slight harm, less than substantial harm or substantial harm. These terms should be used carefully and supported by explanation.

Beneficial effects improve the condition, understanding or appreciation of an asset.

Neutral effects preserve significance without materially altering it.

Less than substantial harm covers a wide range of effects, from limited harm to more serious but still non-substantial change.

Substantial harm is a high threshold and normally involves serious loss or alteration of significance.

7. Mitigation and Justification

Explain how the design has evolved to avoid or minimise harm. This is often where the assessment can be most useful.

Show that alternatives have been considered. Could an extension be located elsewhere? Could a historic wall be retained rather than opened up? Could a repair use a compatible lime mortar rather than cement? Could a new service route avoid cutting through important fabric?

Where harm remains, explain why it is necessary and why the benefits of the proposal justify it. Public benefits may include securing the long-term use and repair of a building, improving accessibility, removing damaging later alterations, providing housing or supporting community use.

Set out practical mitigation measures. These may include photographic recording, measured surveys, archaeological watching briefs, retention of removed fabric, careful opening-up works, reversible detailing, repair before replacement and the use of breathable, compatible materials.

Part 2: HIA Quality Checklist

Phase A: Understanding the Asset

□ Have you checked whether the site is listed, in a conservation area, near another heritage asset or subject to archaeological interest?

□ Have you consulted the Historic Environment Record and appropriate historical maps?

□ Does the report describe the building, site or setting accurately?

□ Does it explain why the asset is significant, rather than merely repeating the list description?

□ Have archaeological, architectural, artistic and historic interests been considered?

□ Have you identified which parts of the asset are of high, medium and low significance?

□ Have you assessed the contribution of setting, including views, landscape and functional relationships?

Phase B: Evaluating the Change

□ Are the proposed works described clearly and supported by drawings or photographs?

□ Are construction methods and materials explained where relevant?

□ Is each proposed change assessed against the significance identified earlier?

□ Does the report explain the likely effect rather than relying on general statements?

□ Is the scale of any harm stated clearly and realistically?

Phase C: Mitigation and Justification

□ Does the report show how harm has been avoided or reduced through design development?

□ Have realistic alternatives been considered?

□ Where historic fabric is to be lost or altered, is there a clear and convincing justification?

□ Where less than substantial harm is identified, are the public benefits explained clearly?

□ Are mitigation measures practical, proportionate and capable of being secured through conditions?

□ Does the proposal follow sound conservation principles, including repair before replacement and the use of compatible, breathable and repairable materials?