Less than substantial harm and the balancing exercise
Less than substantial harm is weighed against public benefits, but great weight and the statutory duty put a thumb on the scales. Here is how to write the balance properly.
Most heritage cases turn on a single judgement: whether the harm is substantial or less than substantial. Get that wrong and the whole assessment collapses, because the two categories lead to different policy tests with very different chances of success. Less than substantial harm is weighed against the public benefits of the proposal. Substantial harm has to clear a much higher bar.
What follows deals with England and with designated heritage assets: listed buildings, conservation areas, scheduled monuments, registered parks and gardens, protected wreck sites and World Heritage Sites.
Where the harm categories come from
National policy divides harm to a designated asset into two bands and attaches a different test to each. The Framework in force was published on 17 August 2026 and is organised by policy code rather than paragraph number, following the December 2024 edition which renumbered the December 2023 text. Cite the edition you are relying on and verify the code, because heritage submissions are read closely and a stale paragraph number undermines everything after it.
The bands sit on top of a statutory duty that does not come from policy at all. Sections 66 and 72 of the Planning (Listed Buildings and Conservation Areas) Act 1990 require decision-makers to have special regard to the desirability of preserving a listed building and its setting, and to pay special attention to preserving or enhancing the character or appearance of a conservation area. The Court of Appeal in Barnwell Manor Wind Energy Ltd v East Northamptonshire District Council held that the section 66 duty requires considerable importance and weight to be given to the desirability of preserving the setting of a listed building, and that a finding of less than substantial harm does not dilute it.
That is the point practitioners most often miss. Less than substantial does not mean less than important.
Identifying the level of harm on the evidence
Substantial harm is a high test. It is generally understood to mean harm that would drain away or vitiate a large part of what makes the asset significant, not merely harm that is noticeable or regrettable. Total loss of an asset is clearly substantial. Demolition of a principal elevation is likely to be. A new building in the setting of a listed building, however unwelcome, usually is not.
The assessment has to start from significance rather than from the proposal. Identify what the asset is, what makes it important, which of its attributes carry that importance, and how each one is affected. An assessment that describes the proposal at length and the asset briefly has the structure the wrong way round.
Three habits improve the finding.
- Attribute significance to specific elements rather than to the asset as a whole, so the effect can be tied to what is actually being changed.
- Describe the effect before naming the category, so the conclusion follows the reasoning rather than the other way around.
- Say where within the less than substantial band the harm falls, because a decision-maker weighing harm at the lower end against benefits is doing a different exercise from one weighing harm at the upper end.
A Heritage Statement that does those three things gives the officer something to adopt. One that asserts a category without showing the working invites the officer to reach their own, usually higher, view.
Great weight and the statutory duty
Policy requires great weight to be given to the conservation of a designated asset irrespective of whether the harm is substantial or less than substantial, and the more important the asset the greater that weight should be.
Two consequences follow for the way a case is written.
The balance is not a simple comparison of two quantities. Harm enters the scales with a thumb already on them, and benefits have to be correspondingly clear. A report that treats heritage harm as one consideration among many, weighed neutrally, misstates the exercise and is vulnerable on challenge.
And the statutory duty runs alongside the policy test rather than being satisfied by it. A decision that works through the policy balance without addressing sections 66 and 72 has a gap in it. The relationship between the two is set out further in sections 66 and 72 and what they require of decisions.
Public benefits that count in the balance
Public benefits must be public. A benefit that accrues only to the applicant does not qualify, however real it is.
Benefits that are commonly accepted include heritage benefits such as repair of the asset, removal of harmful later additions, securing an optimum viable use, and improved public access or interpretation. Wider benefits also count: housing delivery where supply is short, employment, regeneration of a neglected site, environmental improvement, and enabling development where the proceeds are tied to repair of the asset.
Three tests separate a benefit that carries weight from one that does not.
- Is it public rather than private?
- Is it certain enough to be relied on, or is it an aspiration?
- Is it proportionate to the harm, in kind as well as in scale?
The third is the one inspectors probe. A commuted payment towards an unrelated project rarely balances harm to a listed building, whatever its size. Repair of the same building usually does.
Securing the benefits
A benefit that is not secured is a benefit that may not happen, and decision-makers discount accordingly.
Conditions work for matters within the application site and within the applicant's control: a repair schedule, a phasing requirement tying restoration to occupation, a materials condition, a requirement for recording before works. Obligations under section 106 work for matters needing payment, land transfer, long-term management or off-site delivery.
Tie the benefit to the harm in the mechanism itself. A condition requiring repair of the historic fabric before occupation of the new element makes the exchange explicit. A section 106 obligation that hands over money at an unrelated trigger point does not.
Where the case rests on an optimum viable use argument, the viability evidence has to be capable of being tested, and the obligation should capture what happens if the assumed use fails.
How inspectors have approached the weighing
Appeal decisions are indicative of approach rather than binding, and they should be described that way. Read enough of them and consistent themes appear.
Inspectors tend to be unimpressed by assessments that skip the significance stage. They tend to place real weight on securing an optimum viable use for an asset that is deteriorating. They tend to discount benefits that are not secured. They tend to distinguish between harm at the lower and upper ends of the less than substantial band, and to say so explicitly. And they tend to look for the statutory duty to be addressed in terms rather than assumed.
None of that is a formula. It does suggest that the useful work is in the significance assessment and in the securing of benefits, rather than in the advocacy.
Writing the balance so it survives challenge
Set it out in a sequence a reader can follow and a court can check.
State the significance of the asset and the attributes that carry it. State the effect of the proposal on each. Identify the level of harm and where it sits within the band. Record the great weight given to conservation and address the statutory duty in terms. List the public benefits, say how each is secured, and explain the weight given to each. Then state the conclusion and why the benefits do or do not outweigh the harm.
Keep the language precise. Avoid describing harm as minimal when you mean at the lower end of less than substantial, because the first is not a category recognised by policy and invites the argument that the assessment was not carried out properly. Where internal changes are involved, the effect on plan form and fixtures deserves its own treatment, and internal alterations that harm significance is the more detailed companion to this question.
Where the finding is substantial harm, the exercise changes entirely, and the tests that then apply are set out in substantial harm and how it must be justified.
This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it, and verify all policy references against the current published Framework.
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Frequently asked questions
What counts as substantial harm to a heritage asset?
A high test, generally understood as harm that would drain away or vitiate a large part of what makes the asset significant. Total loss clearly qualifies, and demolition of a principal elevation is likely to. A new building in the setting of a listed building, however unwelcome, will usually fall into the less than substantial band instead.
Does less than substantial harm mean the harm is minor?
No. The Court of Appeal in Barnwell Manor held that the section 66 duty requires considerable importance and weight to be given to the desirability of preserving a listed building's setting, and that a finding of less than substantial harm does not dilute that. Policy also requires great weight to be given to conservation whatever the level of harm.
Which public benefits count in the heritage balance?
Benefits must be public rather than private. Heritage benefits such as repair, removal of harmful additions, securing an optimum viable use and improved access all count, as do wider benefits including housing delivery, employment and regeneration. Each must be certain enough to be relied on and proportionate to the harm in kind as well as in scale.
How should a public benefit be secured?
By condition where the matter sits within the application site and the applicant's control, such as a repair schedule tied to occupation or a recording requirement. By section 106 obligation where payment, land transfer, long-term management or off-site delivery is involved. Tie the mechanism to the harm, because an unrelated trigger point attracts less weight.
Do appeal decisions bind a later heritage decision?
No. They are indicative of how inspectors have approached an issue rather than binding precedent, and should be described that way in submissions. Consistent themes do emerge, including scepticism about assessments that skip the significance stage and discounting of benefits that are not properly secured.
Sources and further reading
This article is general guidance about the planning system in England and, where stated, the rest of the UK. It is not legal or professional advice. Check your local planning authority’s validation requirements and take professional advice for your specific site.