Budgeting a viability assessment and its review mechanism
The appraisal is the smallest line. Benchmark land value evidence, the authority's independent review and months of negotiation are where a viability case really costs.
A viability assessment cost is not one fee. It is the appraisal itself, the land value evidence that sits underneath it, the authority's independent review which the applicant usually pays for, and several months of negotiation time that nobody puts in the budget. On a scheme where affordable housing is the point in dispute, the negotiation is the expensive part.
Start from the position national guidance sets. Where plan policies are up to date and the site was allocated or assessed at plan stage, viability should not need to be tested again at application stage. A site-specific assessment is the exception, and the applicant has to justify why it is needed.
What the assessment has to contain to be taken seriously
An appraisal that officers will engage with follows the standardised inputs set out in planning guidance and the professional statement on financial viability in planning published by the surveying institution. Anything that looks tailored to produce a predetermined answer gets sent to the reviewer with a covering note saying so.
The core content is settled: gross development value built from evidenced sales values, build costs from a recognised cost base with an itemised abnormals schedule, professional fees, finance, marketing and sales, all policy contributions including affordable housing and infrastructure levy liability, and the benchmark land value. Developer return is where guidance gives a figure: a return of 15 to 20 per cent of gross development value may be considered a suitable return for market housing, and around 6 per cent for the affordable element.
Use those figures as the starting point and explain any departure. A 25 per cent return assumption on a low-risk scheme invites the reviewer to rewrite the appraisal.
Sensitivity testing is not optional in practice. Run the appraisal across a range of values and costs and show where the scheme tips, because a single-point answer is easy to dismiss. And publish the assumptions clearly enough that the reviewer can rebuild the model.
Benchmark land value evidence and its cost
Benchmark land value is the single most contested input, and it is where most of the specialist fee goes. Guidance requires it to be established on the basis of existing use value plus an appropriate premium to the landowner, with market evidence used as a cross-check rather than as the primary basis.
The price actually paid for the land is not a justification for failing to comply with policy. That sentence has resolved more arguments than any other in the guidance, and it is worth quoting to a client who bought at a residential value and now wants the affordable housing reduced.
Establishing existing use value properly means a valuation of the land in its current use, evidenced from comparable transactions of land in similar use, plus a reasoned premium. That is valuation work requiring a registered valuer, and it is priced separately from the appraisal modelling. Where the existing use is agricultural or industrial with a live occupier, add the cost of establishing the income stream.
Budget for a second opinion. A benchmark land value the reviewer rejects costs more to defend than it did to produce.
Independent review commissioned by the authority and who pays
Councils do not assess viability in house. They commission an independent reviewer, and they expect the applicant to meet that cost, usually through a signed undertaking or a planning performance agreement before the review starts.
Plan for two rounds. The reviewer produces a report, the applicant responds, and the reviewer comments on the response. Each round is chargeable, and a poorly evidenced first submission doubles the number of rounds rather than shortening them.
Ask three things at the outset: who the reviewer will be, what the fee basis is, and what happens if the reviewer and the applicant cannot agree. Some authorities will accept a joint instruction to a single reviewer, which is faster and costs less than adversarial exchanges.
Early and late stage review mechanisms
Where an authority accepts a reduced contribution on viability grounds, it will almost always secure a review mechanism in the section 106 agreement. Two forms are common.
| Mechanism | Trigger | Effect |
|---|---|---|
| Early stage review | Development not substantially started within a stated period after permission | Appraisal re-run on current values and costs; contribution recalculated before build-out |
| Late stage review | A stated proportion of units sold, or practical completion | Surplus above the agreed return shared with the authority, often capped at the policy-compliant figure |
Both carry real cost. Each review is an appraisal exercise with the authority's reviewer paid for again, and the late stage review requires audited sales and cost records to be kept and produced. Build the record-keeping obligation into the development monitoring from day one, because reconstructing it at the end is expensive and disputes over what counts as a cost are common.
Negotiate the cap and the sharing formula carefully. An uncapped late stage review turns an upside into the authority's rather than the developer's, and lenders read those clauses closely. The interaction with levy liability is worth modelling at the same time, using the method in our note on working out CIL liability from a charging schedule.
Disclosure and publication expectations
Assume the appraisal will be published. Guidance is that viability assessments should be made publicly available, and that where a case is made for withholding commercially sensitive detail, an executive summary must still be published.
That has two budget consequences. A document written for publication takes longer to prepare than an internal model, and it needs a separate summary. And commercially sensitive land transaction detail may have to be handled through a redaction request that the authority may refuse.
Write it accordingly from the start. Rewriting an appraisal for publication after a refusal to redact is wasted fee.
Negotiation time as the largest hidden cost
The appraisal takes weeks. The negotiation takes months, and the cost is carried in professional time, extended option payments, finance and the delay to first revenue.
Three practical ways to shorten it. Submit the viability case with the application rather than raising it after a draft heads of terms arrives, because a case introduced late reads as a negotiating tactic. Offer a review mechanism up front instead of resisting one. And put the affordable housing position in the Affordable Housing Statement in the terms the policy uses, so the officer can see precisely which requirement is not being met and by how much.
Where the scheme also carries biodiversity obligations, the cost of those units and their monitoring should be inside the appraisal from the outset, as set out in budgeting biodiversity net gain units, credits and monitoring. Contributions omitted at appraisal stage reappear as reviewer adjustments.
Where the assessment will not help you
A viability assessment cannot fix a scheme that does not work. If the numbers only close by removing most of the affordable housing on an allocated site with an up to date policy, the honest advice is that the land was bought at the wrong price or the scheme needs redesigning.
It also will not help where the deficiency is in the evidence base rather than the economics. A reviewer who cannot verify the sales values or the abnormals schedule will not accept the conclusion, however well the model is built.
And it carries no weight on matters outside viability. Design, heritage harm and highway safety are not traded against the return.
The Viability Assessment report page sets out what the document covers and who is expected to prepare it. Councils expect a suitably qualified author, normally a registered valuer, and professional review of any AI-assisted draft is strongly advised before submission. For the cost of producing supporting documents themselves, PlanScope pricing sets out the free report, the per-report price and the Professional tier.
PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval. For specialist technical reports, qualified professional input may be required.
This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it.
Frequently asked questions
When is a site-specific viability assessment actually needed?
Rarely, in principle. National guidance expects viability to be addressed at plan-making stage, so where policies are up to date and the site was allocated or assessed then, it should not need retesting at application stage. The applicant has to justify why the circumstances warrant a fresh assessment, and weak justification is itself a reason for refusal to engage.
What developer return does guidance suggest?
A return of 15 to 20 per cent of gross development value may be considered suitable for market housing, with around 6 per cent for the affordable element. Use those as the starting point and explain any departure with evidence about the risk profile of the particular scheme. Unexplained higher assumptions get rewritten by the authority's reviewer.
How is benchmark land value established?
On the basis of existing use value plus an appropriate premium to the landowner, with market evidence as a cross-check rather than the primary basis. It requires a valuation of the land in its current use, supported by comparable transactions, and a reasoned premium. The price actually paid is not a justification for failing to comply with policy.
Who pays for the council's independent reviewer?
The applicant, almost always, secured through a signed undertaking or a planning performance agreement before the review begins. Budget for at least two rounds, since the reviewer reports, the applicant responds and the reviewer comments again. A poorly evidenced first submission increases the number of rounds rather than shortening the process.
What is the difference between an early and a late stage review?
An early stage review is triggered where development has not substantially started within a stated period, and re-runs the appraisal on current values before build-out. A late stage review is triggered by sales progress or practical completion, and shares any surplus above the agreed return with the authority, usually capped at the policy-compliant contribution.
Will my viability appraisal be published?
Assume so. Guidance is that viability assessments should be made publicly available, and where a case is made for withholding commercially sensitive detail an executive summary must still be published. Write the document for publication from the outset and prepare the summary alongside it rather than retrofitting both after a redaction request is refused.
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.