Heritage impact assessment: what they are and when you need one

If you’re planning to alter an historic building or develop near one, you may need to order a heritage impact assessment. Windsor Patania has a 97% success rate with planning and licensing across 200 councils.

Read on to find out more about when you need a heritage impact assessment, what it includes, and how to get it right.

WindsorPatania note: You may see heritage impact assessments referred to by other names. They include “heritage impact statement”, “historic building impact assessment” or “heritage statement”. They’re all part of the same planning process but the title varies between different councils.

What is a heritage impact statement or assessment?

A heritage impact assessment is a planning document that does two things:

• Explains what makes your building or site historically important
• Shows how your planned changes will affect that importance.

The National Planning Policy Framework (NPPF) requires councils to take care of historic buildings and sites. This includes having a strategy for the conservation and enjoyment of the historic environment.

Part of their role is to get impact statements for developments affecting historic assets. So, your local planning authority needs this information before they can approve your plans.

This includes non-designated heritage assets. They are buildings, sites and features councils consider of local interest that are not nationally listed. Check with your council if there are any in your area.

WindsorPatania note: Heritage Impact Assessments are often a key part of a Design and Access Statement (DAS). A DAS is a planning document that explains the design thinking behind a build proposal.

When you need a heritage impact assessment

You need an assessment when your development could affect a heritage building or its setting.

Listed buildings and listed building consent

Every listed building consent application (November 2023) must include a heritage impact assessment as part of the listed building consent applications . This applies even to small changes. The rule covers alterations, extensions, and demolition.

Different listing grades affect what you need to submit:

Changes affecting a listed building’s setting also need an assessment. The setting is the surroundings of a building. This can include gardens and curtilage, nearby streets and spaces and views to and from the building.

Occasionally, development of a non-listed building can affect an existing building. Examples include a tall rear extension that blocks the view of a church or bright signage on the building next door. In these cases, you need to show how your proposal will affect the listed building and how you’ll reduce harm.

The protection applies to the inside and outside of listed buildings. So, internal changes like getting rid of original panelling and external changes like changing a window need to gain consent.

Standard planning permission doesn’t cover works to listed buildings.

Conservation areas and non-designated assets

A conservation area is a place recognised for its special architectural or historic interest. Local authorities and governments declare them as such because they want to preserve or enhance their character.

Examples include Victorian suburbs, historic town centres, and model villages or estates. They enjoy protection because of their special nature.

If you want to develop in a conservation area, your local planning authority can ask for a heritage impact assessment. They’ll want the following useful information:

In the existing guidance, World Heritage Sites are assets of the highest significance. Sites in the UK include Stonehenge, Bath city centre and the Tower of London.

Any proposed changes that affect these sites need a very detailed assessment and planning application. Use the 2022 UNESCO Guidance and Toolkit for Impact Assessments and follow any local management plan. Your council will tell you exactly what to provide based on the scale and type of your proposal.

What goes into a heritage impact assessment

Your assessment is a two part process. First, it tackles significance first, then it looks at impact.

Heritage significance

Significance is why a heritage asset matters now and why it will matter in the future.

Historic England splits heritage value into four types. Understand these and this will give you a base for assessing the potential impact of your development.

The four heritage values explain why an asset is important:

• Evidential value: What an asset reveals about past human activity
• Historical value: How past people, events and life connect through the place to the present day
• Aesthetic value: The sensory and intellectual response people get from an asset’s design, materials and so on.
• Communal value: What the place means to people who relate to it or for whom it forms part of our collective memory

Not every building scores equally on all four. For example, a Georgian townhouse might look beautiful but, if it’s altered, there’d be very little new evidence. Alternatively, a Roman ruin might not be much to look at but begin to excavate it and you could uncover rare finds that add to our understanding of the time.

When carrying out your assessment, identify which of the four heritage values apply to it.

Heritage impact

Once you know what matters, the next step is to assess how your plans affect it. There is a process you should follow to ensure you don’t overlook anything.

The four stage process is:

• Identify all heritage assets potentially affected: Look around your site to find every asset your plans might impact.
• Explain the significance of affected assets: Describe the importance of the asset. Use the four heritage values from the first step.
• Describe the likely impact on this significance: Show how your proposed works affect each part of significance.
• Provide an overall assessment: Weigh up harms against public benefits and find ways to reduce harm.

In heritage assessment, impact exists on a spectrum. What you want to do might enhance significance by revealing hidden features or restoring previous damage. You might want to go out of your way to preserve significance by keeping the existing character.

They might also cause harm. For example, removing part of a historic wall in a property to create open-plan living. Your assessment must be honest and reflect the potential positives and negatives of your plan.

Look for ways to balance protecting the building and achieving your goals. You might adjust designs, choose different materials, or carry out works in stages to protect the features that matter the most.

The proportionality principle

The proportionate assessment requirements refer to the level of detail you go into. Provide no more than is sufficient to understand the potential impact. Make sure your level of detail matches the asset’s importance and the scale of work.

For example, the potential impact of minor changes to a Grade II listed building might only need a short assessment, containing:

• Descriptions of the affected parts
• Explanations of their importance
• How your plans will preserve character

Back up your evidence with photos and drawings to build your case.

Larger projects affecting important assets need a much more thorough assessment. In your application, you’d also include:

• Historical research
• Lots of photos and images
• A careful analysis of the setting
• Measured surveys

It can be difficult to guess proportionality. Contact your local planning authority to get them to assist you. They’d rather be dealing with you now to help you at the pre-application stage. They can stop you from preparing too little or too much. Their contribution could be invaluable in identifying key issues for your application. Ask them about their methodology behind how they come to a judgement.

Occasionally, developers ask planning decision makers about demolishing a building. For serious proposed works like this, you need a very strong case, regardless of significance and impact.

Who can help you with a heritage impact statement?

You could try to create your own Heritage Impact Assessment. Be aware though that these are documents that normally need someone with proper heritage experience.

For straightforward Grade II projects, an experienced heritage consultant should work well. More complex projects need specialists with specific qualifications.

When choosing a professional, look for members of:

• Chartered Institute for Archaeologists
• Institute of Historic Building Conservation
• Royal Institute of Chartered Surveyors

These groups maintain very high standards through programmes of ongoing training.

For major changes to Grade I listed buildings or projects that affect World Heritage Sites, choose a senior consultant. They are also suitable for developments likely to cause substantial harm. Your council might require specific qualifications and a level of expertise in your advocate.

Heritage statement pricing varies a lot based on complexity. Basic desk work starts around £500. Comprehensive assessments with extensive research and multiple visits can top £2,500. Most home projects fall in the middle.

Here are examples of typical heritage statement costs:

Most consultants quote fixed prices after an initial chat, which is a two part process. They’ll review your project and site before committing to a price.

These factors are likely to push up your price:

• Buildings with little recorded history
• Projects affecting multiple heritage assets
• Rush jobs
• Remote locations

WindsorPatania: experienced planning architects

Working with heritage assets involves risk. Planners will hold you to account before and after any building work. You’ve got to work within their conservation principles and regulations while still delivering a viable project.

WindsorPatania has a 97% success rate in planning and licensing building projects. Our team of architects has experience working with over 200 councils. We know how they like to conduct the planning process and the context we need to place your project in to help it succeed the first time.

We offer end-to-end architecture services on all build projects, including:

• Architectural consultation: Advice before you purchase and on your project design plans and goals.
• Feasibility studies: New build feasibility, retrofit feasibility, sustainability assessments and private residence design appraisals.
• Architectural services: Residential new build, residential retrofit, Grand Design homes, home extensions, commercial architecture, education and retail.
• Project management: Pre-construction project management and construction project management from concept to completion.

To tell us about your heritage property or landscape project, simply submit a project, email us or call us. We look forward to discussing your idea with you.