The end of “less than substantial”: how the new NPPF redefines harm

For more than fourteen years, almost every heritage assessment written in England has reached for the same phrase. The proposal would cause less than substantial harm. The harm should therefore be weighed against public benefits. Everyone knew what it meant, everyone used it, and a good deal of professional judgement was quietly parked behind it. The NPPF substantial harm test has replaced it.

That phrase has now gone. The new National Planning Policy Framework restructures the historic environment as Chapter 20, policies HE1 to HE10, and in doing so it changes not just the vocabulary of harm but the obligation that sits behind it. This is the most consequential change for anyone preparing or determining an application affecting a listed building, and it is worth understanding precisely.

What the policy now says

Policy HE5 governs the assessment of effects. It requires every proposal affecting a heritage asset to be accompanied by an assessment of significance and of the potential effect on that significance. It then requires that assessment to place the proposal in one of four categories: a positive effect, no effect, harm, or total loss of significance.

The critical sentence sits in the third of those. Where a proposal would result in harm, “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.”

Two obligations follow. The degree of harm must be identified, not merely asserted. And substantial harm now has a definition in national policy for the first time since 2012.

The NPPF substantial harm test, defined downwards

The definition will look familiar to anyone who has read the Planning Practice Guidance. The formulation about seriously affecting a key element of a building’s special interest has sat in the PPG for years. What has changed is its status. It has been promoted from guidance into policy, and in the process it displaces the higher threshold that came out of the courts.

The 2013 judgment in Bedford Borough Council v Secretary of State for Communities and Local Government and Nuon UK Ltd [2013] EWHC 2847 (Admin) had set the bar at a point where the significance of an asset would be vitiated altogether or very much reduced. On that reading there was very little daylight between substantial harm and total loss, and in practice the substantial harm category was reserved for demolition and near-demolition. There was always a tension between that and the PPG. The new Framework resolves it, and resolves it in favour of the lower threshold.

The distinction matters enormously. Under Bedford, you asked whether the significance of the whole asset survived. Under HE5, you ask whether a key element of that significance would be seriously affected. An intervention that guts the historic plan form of a farmhouse while leaving its elevations intact was comfortably less than substantial under the old test. It is a much more difficult argument now.

Practitioners who have spent a decade assuming that substantial harm is somebody else’s problem should expect it to arrive on ordinary casework.

The empty half of the scale

Here is the trap. The Framework labels one point on the harm spectrum and one only. Below substantial harm there is simply harm. There is no policy category called less than substantial harm, no glossary definition of harm or of its gradations, and no national scale to select from.

So when policy says the degree of harm should be identified, it is not inviting you to choose from a menu. It is requiring you to construct a reasoned position and defend it. If an assessment uses a low, moderate and high scale, or a minor to major scale, it must say that this is the assessor’s own scale, define what each rung means, and demonstrate how the proposal was placed on it. A bare adjective is no longer an answer.

The other half of that discipline is granularity. A scheme is rarely one thing. Reroofing, a rear extension, the removal of a partition and the insertion of rooflights will each engage different elements of significance to different degrees. The assessment should locate each of them, then draw them together into an overall position, rather than applying a single label to the whole and hoping it holds.

And note policy HE5(3): it is the effect on significance, not the scale of the development, that is to be assessed. A small intervention in a highly sensitive element can rank higher than a large one in a later addition of little interest. Floor area is not a proxy for harm.

Why the label decides the outcome

The reason all of this matters is that the category chosen is the gateway to the test that gets applied.

• Where harm falls below the substantial threshold, policy HE6(4) applies. The effect on the asset is weighed against the public benefits of the proposal. The new Framework helpfully names two: securing the long-term reuse of a vacant or underused listed building, and enabling energy efficiency and low carbon heating measures.
• Where harm is substantial, or would cause total loss, policy HE6(5) applies instead. Consent should be refused unless the harm is necessary to achieve substantial public benefits that outweigh it, or a four-limb test on reasonable use, marketing, grant funding and reuse is satisfied in full. HE6(6) then adds that such harm should be exceptional for grade II assets and wholly exceptional for grade I and II* assets, scheduled monuments, registered battlefields and World Heritage Sites.

Those are not two points on a sliding scale. They are two different tests with very different prospects of success, and the assessment of degree determines which one the application is judged under.

Throughout, policy HE6(1) requires substantial weight to be given to conservation, and HE6(3) confirms that any harm to a designated heritage asset is a matter of considerable importance and weight. The statutory duty under section 16 of the Planning (Listed Buildings and Conservation Areas) Act 1990 to have special regard to the desirability of preserving the building, its setting and its features of special interest is untouched by any of this, as is the section 72 duty to pay special attention to the desirability of preserving or enhancing the character or appearance of a conservation area.

It is worth being clear about what all this applies to, because the argument is usually framed around listed buildings and the reach is wider. The Framework’s glossary defines a designated heritage asset as a World Heritage Site, scheduled monument, listed building, protected wreck site, registered park and garden, registered battlefield or conservation area. HE6 therefore applies to conservation areas in full, and substantial harm to a conservation area engages HE6(5) exactly as substantial harm to a listed building does. The assessment obligation in HE5 is wider still, being expressed to apply to heritage assets, which the glossary defines to include assets identified by the local planning authority through local listing.

One asymmetry is worth having in mind. HE6(6), which requires substantial harm to be exceptional or wholly exceptional according to the asset, names listed buildings and registered parks and gardens by grade, together with scheduled monuments, protected wreck sites, registered battlefields and World Heritage Sites. Conservation areas appear in neither list. Substantial harm to a conservation area therefore engages HE6(5) but does not attract the exceptionality overlay, unless it is argued in as an asset of the highest significance under the word notably.

Policy HE7 then imports the same substantial harm and total loss language into decisions on non-designated heritage assets, so the obligation to identify degree does not stop at the designated boundary. The label does different work there: HE7(3) asks whether the harm or loss is outweighed by the benefits, having regard to the scale of the harm and the significance of the asset, rather than applying the HE6(5) test. Footnote 64 adds that a non-designated asset of archaeological interest which the decision-maker considers of equivalent significance to a scheduled monument should be considered under the policies for designated assets.

The decision-maker as auditor

The final change is the one most likely to cost applicants consent. Policy HE5(4) states that decision-makers should be satisfied that assessments accurately reflect the effects on heritage assets caused by development proposals.

That is an express invitation to reject an assessment that does not. Understating harm has always been a poor tactic. It is now a route to refusal in its own right, because an authority that does not accept your characterisation has policy backing to say so, and to determine the application on its own view of the degree of harm instead.

The honest assessment, which identifies real harm, locates it accurately and then argues the balance on its merits, has always been the stronger document. Under the new Framework it is also the safer one.

What this means in practice

A Heritage Impact Assessment that will survive contact with a conservation officer now needs to do four things:

1. Establish significance element by element, so that there is something concrete against which effects can be measured.
2. Assess each part of the proposal against the elements of significance it actually engages.
3. State the scale of harm being used, define it, and place each effect on it with reasons.
4. Carry the resulting position into the correct balance under HE6, and make the public benefits case with evidence rather than assertion.

None of that is new as good practice. What is new is that it is now policy, and that a decision-maker has express authority to test whether you have done it.

All of which rests on reading the fabric

Every one of those four steps depends on the first. You cannot identify the degree of harm to an element of significance until you know what that element is, when it was built, how it was made, and what it tells you about the building’s development. Get that wrong and everything downstream is guesswork, however confidently it is written up.

This is where a great many assessments come apart. A partition is described as modern when it is early. A roof structure is treated as a later alteration when it is the original frame. Joinery is called a Victorian replacement because it has been painted, when the section, the joints and the tooling all say otherwise. None of those errors is visible in the finished document. All of them are fatal to the assessment of harm, and all of them are the sort of thing a conservation officer will find on site.

Reading fabric is a practical skill, learned by handling buildings rather than by reading about them. At Heritage Unlimited it comes from two directions. Our Director came into conservation through the trade, as a joiner, before taking a BA (Hons) in Architectural Conservation, and that combination of bench experience and formal training in building pathology, materials and historic construction is what allows a building to be read from the fabric itself rather than from the list entry. Our senior consultant came to heritage consultancy from architectural practice, with years spent on major conservation projects, and brings the same understanding from the design and repair side.

The practical effect is that when we say an element is of high significance, or that a proposed intervention would seriously affect a key element of it, that judgement is founded on evidence we can point to in the building and defend in writing.

This is the first of two pieces on the new Framework. The second, on what survives of more than fourteen years of heritage case law and where Local Plans now stand, follows tomorrow.

Heritage Unlimited prepares Heritage Impact Assessments, setting assessments and listed building consent advice for owners, architects and planning consultants across England. If you are planning works to a listed building, we can establish what is significant and why, and support your application with an assessment that will stand up to scrutiny. If the degree of harm is going to be contested, we would be glad to talk it through.