Heritage at risk and optimum viable use

Optimum viable use is the use of a heritage asset that causes the least harm to its significance, rather than the use that produces the most money. That distinction sits at the centre of every application involving a building on a heritage at risk register, and it is the test a council will apply when a developer argues that only a particular scheme can save the building. Getting optimum viable use heritage arguments right means ranking uses by harm first and testing viability second, in that order.

Do it the other way round and the assessment reads as a justification written backwards from the preferred scheme.

What optimum viable use means in policy

National planning guidance describes the optimum viable use as the one likely to cause the least harm to the significance of the asset, taking account of the initial changes needed and also of subsequent wear and tear and the alterations a use will generate over time. The current National Planning Policy Framework, published on 17 August 2026 and arranged by policy code, carries the concept in its historic environment chapter, and asks decision makers to assess whether a proposal for a building at risk secures its conservation.

Two elements of that definition get overlooked. The first is the long view: a use that needs little initial intervention but generates constant small alterations may harm significance more than a use requiring one substantial change. Residential conversion of a large industrial hall is the standard example, where subdivision, services, fire compartmentation and fenestration accumulate.

The second is that the asset's significance sets the test, so the assessment has to start from a proper understanding of what is important about the building and why.

Why it is not the most profitable use

Guidance is explicit that the optimum viable use may not be the most profitable one. Viability enters the analysis as a filter rather than as the objective.

The sequence that works is straightforward. Identify every use the building could physically and lawfully accommodate. Assess the harm each would cause to significance, including the harm from subsequent adaptation. Rank them from least harmful to most. Then test each in turn for viability, starting at the least harmful end, and stop at the first one that works.

If the least harmful use is viable, that is the optimum viable use, even where a more harmful use would return more. Where several uses are viable, the least harmful of them is the answer. And where none is viable at all, you are into enabling development territory, which is a different argument with its own tests.

Building the options appraisal

An options appraisal that persuades is a short document with real content, not a table of five uses and a paragraph each.

For each option, set out what physical interventions it requires, how those interventions affect the elements that carry significance, what consents would be needed, what the capital cost of repair and conversion would be, what end value or rental income it would produce, and what the residual is. Use consistent assumptions across options, and state them.

Include the do-nothing option honestly. A building continuing to deteriorate has a cost, and quantifying the additional repair liability that accrues over five years is often the most useful number in the document.

Where the building is structurally compromised, a Structural Survey establishing the actual condition should precede the appraisal, because repair costs assumed without opening up are usually the weakest figures in the file.

Marketing evidence councils accept

When the argument is that no lower-harm use is viable, councils will want marketing evidence, and the quality of that evidence decides a lot of cases.

A defensible marketing exercise runs for a meaningful period, commonly at least 12 months, through an agent experienced in that building type and that market. The asking price reflects the condition of the building and the constraints of its designation, rather than a value that assumes unconstrained development. Marketing covers all the uses identified in the appraisal rather than only the one you want. And the record includes the particulars, the channels used, the enquiries received, the viewings held, the offers made and the reasons each was not pursued.

The failures are predictable. Three months on one website at a price that assumes residential conversion already consented. No approach to the specialist operators who buy that type of building. An asking price justified by a valuation that ignores the repair liability. Officers see these regularly and discount them.

Deliberate neglect and how it is treated

National policy is direct on this. Where there is evidence of deliberate neglect of, or damage to, a heritage asset, the deteriorated state of the asset should not be taken into account in the decision.

The practical effect is that an owner who has allowed a building to decay cannot then rely on the decay to argue that only a harmful scheme is viable. Councils apply this more often than developers expect, particularly where an ownership history shows a purchase, a refused application, and then several years of open roofs.

If you are buying a building at risk, document its condition at acquisition. That record separates you from the previous owner's conduct, and it is worth more than any argument you can make later.

Statutory tools the council can use

Councils are not limited to refusing applications. Several powers exist, and they change the negotiating position when they are on the table.

These are used sparingly because they cost councils money and officer time. They are used more readily where a building is prominent, well loved locally, and owned by someone who has ignored correspondence.

Enabling development and the conservation deficit

Where no viable use exists for the heritage asset on its own, enabling development is the recognised route: an amount of development that would otherwise be contrary to policy, justified because it funds the conservation of the asset.

The arithmetic is the conservation deficit, which is the cost of repair and conversion plus a reasonable developer return, less the end value of the restored asset. The enabling development should generate no more than that deficit. Anything above it is profit the council will strip out.

Expect scrutiny of every input. Repair costs need to come from a measured schedule rather than a rate per square metre. Developer return should be justified against the risk profile. The end value needs comparable evidence. Because the Viability Assessment is the document carrying all of this, councils usually expect a suitably qualified author and often appoint their own reviewer at the applicant's cost, so professional review is strongly advised.

Delivery matters as much as arithmetic. The obligation should tie the enabling development to the heritage works by phasing, with the repairs completed or bonded before the profitable element is occupied.

Presenting the case

Lead the Heritage Statement with significance, then harm, then the options appraisal, then viability, then delivery. That order mirrors how the decision maker has to reason, and it makes the officer's report easier to write.

Say plainly where harm arises and at what level, rather than describing every intervention as sensitive. A statement that identifies less than substantial harm at the upper end, and then sets out the public benefit of securing a building's future against it, is more credible than one claiming no harm at all. Include the Historic Building Recording proposals where fabric is being lost, and say who will carry them out.

But get the building watertight first if you can. A temporary roof and secured openings, done early and at your own cost, changes how everyone in the room treats the application.

This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it.

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