The less than substantial harm test in practice
Less than substantial harm covers almost everything short of destruction. The work is in locating the harm on the scale and evidencing the benefits against it.
Less than substantial harm is not a low bar. It is the category that captures almost every alteration, extension or nearby development affecting a designated heritage asset, from a rooflight on a Grade II house to a tower in the setting of a cathedral. Once you are in it, the National Planning Policy Framework requires great weight to be given to the asset's conservation and then requires the harm to be weighed against the public benefits of the proposal. The statutory duties in sections 16(2) and 66(1) of the Planning (Listed Buildings and Conservation Areas) Act 1990 sit above that, and the Court of Appeal in Barnwell Manor Wind Energy Ltd v East Northamptonshire District Council confirmed that the duty means considerable importance and weight, not a neutral balancing exercise.
Most heritage cases are lost on the first step rather than the last. If significance is not properly identified, nothing that follows can be assessed.
Significance comes before harm
You cannot describe harm to something you have not described. The order is significance, then the contribution the affected elements make to it, then the effect of the proposal on those elements.
Historic England's advice in Managing Significance in Decision-Taking sets out the sequence, and Advice Note 12 on statements of heritage significance gives the structure most authorities expect. A heritage statement that opens with a list of what is proposed, rather than with what the asset is and why it matters, has already inverted the test.
Be specific about which interests are engaged. Architectural, historic, artistic and archaeological interest are separate, and an asset can be highly significant for its historic associations while being architecturally modest. A proposal that removes a later unsympathetic addition may cause no harm at all, and saying so with evidence is stronger than conceding a small harm to appear reasonable.
Where setting is the issue, the five-step approach in Historic England's guidance on the setting of heritage assets is the method to follow, and the output should be a clear statement of how the setting contributes to significance before any assessment of change.
Where the dividing line sits
The line between substantial and less than substantial harm is high, and the courts have treated substantial harm as serious harm that drains away or vanishes a very large part of the asset's significance. Total loss of a building through demolition is substantial. So is a change that leaves the asset's significance largely destroyed even if the fabric survives.
Almost everything else falls below that line. The consequence is that "less than substantial" spans an enormous range, which is why the useful question is not which category applies but where within the lower category the harm sits.
| Position on the scale | Typical example | What the balance needs |
|---|---|---|
| At the lower end | A conservation rooflight on a rear slope, a modern replacement window matching the original | Modest public benefit, often design-led |
| In the middle | A rear extension removing a historic back wall, a new building in a conservation area replacing a neutral one | Identified, evidenced benefits |
| At the upper end | Loss of a principal elevation feature, development dominating the setting of a Grade I asset | Substantial public benefit, often strategic |
Use that language in the assessment. An officer or inspector who reads "less than substantial harm at the lower end of the spectrum, arising from the loss of the rear scullery wall" can engage with it. One who reads "some harm" cannot.
Great weight and what it does
Great weight is not a tie-breaker applied at the end. It colours the whole exercise, and the statutory duty means the decision maker must give considerable importance and weight to the desirability of preserving the asset and its setting before any balance is struck.
Two practical consequences follow. First, a scheme causing even low-end harm needs a positive case, not merely an absence of objection. Second, the harm cannot be offset by heritage benefits elsewhere in the scheme without those benefits being identified, secured and attributed. A repair programme that would happen anyway is not a benefit.
The Court of Appeal in Mordue confirmed that a decision maker who applies the Framework's heritage policy correctly will normally have discharged the statutory duty, which means the quality of the policy reasoning in your statement does double duty.
What counts as a public benefit
This is where most statements are weakest. Public benefits must be real, must flow from the proposal, and must be public rather than private.
Benefits that routinely carry weight include the sustainable reuse of a vacant or deteriorating asset, securing its long-term maintenance, the delivery of housing where there is a shortfall, economic activity and employment, improvements in public access or interpretation, environmental and carbon improvements, and the removal of harmful later alterations.
Benefits that routinely carry little weight include the applicant's financial return, the convenience of the occupier, compliance with Building Regulations that any scheme would have to meet, and improvements that are promised but not secured by condition or obligation.
Two tests I apply to every claimed benefit. Could it be delivered without the harmful element? If so, it is not a benefit of that element. And is it secured? An unsecured benefit is an intention.
Energy efficiency work is a case where the benefit is real but has to be argued rather than asserted, and our note on secondary glazing and insulation in a listed building sets out the evidence that makes the argument land.
Weighing it transparently
The balance has to be visible. Write it as a short passage that names the harm, locates it on the scale, names each benefit, says what weight it carries and why, and states the conclusion.
Illustrative example. A Grade II farmhouse, vacant for six years, with a failing roof and a 1970s flat-roofed extension. The proposal removes the extension, repairs the roof under a specified schedule, and adds a glazed link to a converted outbuilding that cuts into the rear elevation at one point. Harm: low-end, from the intervention in the rear wall. Benefits: securing the repair of the roof through a condition tied to commencement, the return of a vacant listed building to use, and the removal of an unsympathetic addition. On those facts the balance favours consent. The example is illustrative only, and a real case turns on its own evidence.
What that passage does is make the reasoning reviewable. An officer can adopt it. An inspector can test it. A statement that leaves the balance implicit forces the decision maker to construct it, and they may construct it differently.
Mitigation, conditions and recording
Harm can often be reduced rather than offset. Reversibility, the choice of junction between new and old, the removal of a proposed opening in favour of an existing one, and material and detail specification all move the needle.
Where harm to fabric is unavoidable, recording is mitigation of a limited kind. It preserves information rather than significance, so it reduces the consequences of the harm without reducing the harm itself. Say that plainly rather than presenting a record as a cure. Historic England's recording levels give the framework, and the level should be specified in the application rather than left to a condition.
Conditions that bear directly on the harm are worth offering: approval of a joinery schedule, a mortar specification, a method statement for taking down and rebuilding, and a requirement that the repair schedule is completed before occupation. Our note on replacing a historic shopfront shows how far detail specification can shift an assessment.
How inspectors have approached it
Appeal decisions are not binding precedent and should be read as indicative of approach rather than as rules. Read in that spirit, a few patterns are consistent.
Inspectors expect the harm to be located on the scale and are sceptical of assessments that find no harm at all where fabric is lost. They give little weight to benefits that are not secured. They distinguish between the setting of an asset and the view of it, and dismiss arguments built only on the latter. And they treat the statutory duty as a separate step, so a statement that addresses policy without addressing the duty invites a correction.
Where visual effects on a wider townscape are in issue, a townscape and visual impact assessment alongside the heritage statement gives the decision maker the two different analyses the question needs.
This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.
Frequently asked questions
What is the difference between substantial and less than substantial harm?
Substantial harm is a high test, reserved for change that drains away or vanishes a very large part of an asset's significance, such as demolition. Everything short of that is less than substantial, which covers an enormous range. The practical task is to locate the harm within that lower band rather than to argue about the category.
Does great weight mean a scheme causing harm will be refused?
No. It means the decision maker must give considerable importance and weight to conserving the asset before balancing the harm against public benefits. A scheme with identified, secured benefits proportionate to low-end harm can be approved. A scheme with no positive case will not be, even where the harm is modest.
Can heritage benefits within the same scheme offset the harm?
Yes, where they are real, attributable to the proposal and secured. Repairing a failing roof or removing an unsympathetic later addition both count. Works that would be required anyway, or that could be delivered without the harmful element, do not count as benefits of that element.
Is a building record enough to mitigate the loss of historic fabric?
Recording preserves information rather than significance, so it reduces the consequences of harm without reducing the harm. It is a legitimate but limited form of mitigation. Specify the recording level in the application rather than leaving it to a condition, and do not present the record as curing the loss.
Do I need to address the statutory duty separately from policy?
Yes. Sections 16(2) and 66(1) of the Planning (Listed Buildings and Conservation Areas) Act 1990 impose duties that the Court of Appeal has held require considerable importance and weight. Applying the Framework correctly will usually discharge the duty, but a statement that never mentions it invites a correction.
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.