What is a development viability assessment?

It is an appraisal that tests whether a scheme can meet its planning policy requirements, mainly affordable housing and Section 106 contributions, while still leaving a competitive return for the developer and a reasonable payment to the landowner. It compares the residual land value against a benchmark land value.

What is benchmark land value?

It is the yardstick a viability assessment measures against, defined on an existing use value plus a premium basis (EUV plus). You take the land's value in its current use and add a premium that gives the landowner a reasonable incentive to sell while still allowing the scheme to meet policy.

Does paying a high price for land justify less affordable housing?

No. National policy is clear that the price paid for land is not, on its own, a justification for failing to meet planning obligations. The benchmark is anchored to existing use value plus a premium, so overpaying erodes the developer's margin rather than creating a viability case.

Is viability assessed at plan-making or on application?

Primarily at plan-making, when policies are set and tested for deliverability across the area. Assessment at the application stage is meant to be the exception, for genuinely site-specific reasons, and such assessments are generally expected to be transparent and publicly available.

Development viability assessments and the NPPF

Threshold Guides · 9 min read · England & Wales

A viability assessment is the evidence that connects what a scheme can sell for to what planning policy asks it to deliver. In the English planning system it has a defined role, a defined method and a defined starting assumption about land value, and developers who understand all three negotiate from a stronger position. This guide keeps the policy references general and focuses on how viability actually works and where it touches your land bid.

What a viability assessment is

A viability assessment tests whether a development can meet its policy requirements, chiefly affordable housing and Section 106 contributions, and still leave a competitive return for the developer and a reasonable payment to the landowner. In essence it is a residual appraisal wrapped in a policy framework: gross development value in; build costs, fees, finance and profit out; and a comparison of what is left for land against a benchmark. If the residual can carry policy-compliant obligations and still clear the benchmark, the scheme is viable on policy terms. If it cannot, the assessment becomes the basis for a conversation about what the site can support. The inputs are the familiar ones from any residual appraisal: sold-price evidence for value, build costs, professional fees, finance and a profit target, each of which the authority and its own reviewer will scrutinise line by line.

The NPPF and PPG context

Two documents frame viability in England: the National Planning Policy Framework (NPPF) and the Planning Practice Guidance (PPG) on viability. The framework is deliberately plan-led. The expectation is that viability is tested up front when a local plan and its policies are set, so the policies are already known to be deliverable across the area. Where up-to-date policies exist, the working assumption at the application stage is that they can be met, and the price a developer has paid or agreed for land is not, on its own, a justification for failing to deliver them. Viability at the application stage is the exception, for genuinely site-specific reasons, rather than a routine lever. Assessments are also expected to be transparent and, in most cases, made publicly available.

Benchmark land value: existing use plus a premium

The pivot of any viability assessment is the benchmark land value: the figure the residual land value is measured against. The guidance defines it on an existing use value plus a premium basis, usually written EUV plus. You start from the value of the land in its current use, then add a premium that gives the landowner a reasonable incentive to sell while still allowing the development to meet policy. The premium is meant to reflect a fair return to the landowner, not the full hope value of a consented scheme, precisely so that an inflated land price cannot be used to argue policy away. Getting the benchmark right is where most viability disputes live: set it too high and every obligation looks unaffordable; set it honestly and the assessment means something.

A competitive return

Viability also assumes a competitive return to the developer for the risk of building the scheme out. The guidance discusses developer return in the region of 15-20% of gross development value as a typical reference point, while recognising it can vary with the type and risk of the scheme. The principle is symmetry: a willing landowner should receive a reasonable payment and a willing developer a competitive profit, both assessed against policy-compliant costs rather than against whatever price happened to be agreed. If a scheme only works by cutting the developer's return to the bone, that is a signal the land is overpriced, not that the policy is unreasonable.

How viability interacts with affordable housing and Section 106

Affordable housing is usually the largest single policy cost, and it is where viability most often bites. Because affordable homes transfer at well below market value, a policy-compliant affordable percentage reduces GDV, while Section 106 contributions and CIL add to costs. A viability assessment quantifies whether the scheme can carry the full policy ask. Where it genuinely cannot, the assessment can support a reduced provision, but authorities increasingly protect their position with review mechanisms: clauses that revisit affordable housing if sales values come in higher than assumed, so that improved viability is shared rather than pocketed. See our guide to Section 106 and CIL for how those obligations are structured.

What viability means for your land bid

The practical lesson for a developer is blunt: you cannot buy your way out of policy. Because the benchmark is anchored to existing use value plus a modest premium, overpaying for land does not create a viability case, it just destroys your own margin. The disciplined sequence is to model a policy-compliant scheme first, with full affordable housing, contributions and CIL, and derive the residual land value from that. That residual, not an optimistic land-value-first number, is your maximum bid.

Policy-compliant viability test

Residual land value = GDV (with policy-compliant affordable housing) - build cost - fees - finance - competitive profit.

If the residual is at or above the benchmark land value (existing use value plus premium), the scheme supports policy. If it falls below, either the land price has to come down or there is a genuine, evidenced viability case to examine.

Everything upstream depends on the GDV being real. Build it from local sold evidence rather than aspiration: see live per-square-foot values on our data pages, appraise a specific site with Threshold, and read the residual land value guide for how the numbers combine.

Frequently asked questions

What is a development viability assessment?: It is an appraisal that tests whether a scheme can meet its planning policy requirements, mainly affordable housing and Section 106 contributions, while still leaving a competitive return for the developer and a reasonable payment to the landowner. It compares the residual land value against a benchmark land value.
What is benchmark land value?: It is the yardstick a viability assessment measures against, defined on an existing use value plus a premium basis (EUV plus). You take the land's value in its current use and add a premium that gives the landowner a reasonable incentive to sell while still allowing the scheme to meet policy.
Does paying a high price for land justify less affordable housing?: No. National policy is clear that the price paid for land is not, on its own, a justification for failing to meet planning obligations. The benchmark is anchored to existing use value plus a premium, so overpaying erodes the developer's margin rather than creating a viability case.
Is viability assessed at plan-making or on application?: Primarily at plan-making, when policies are set and tested for deliverability across the area. Assessment at the application stage is meant to be the exception, for genuinely site-specific reasons, and such assessments are generally expected to be transparent and publicly available.

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Data referenced in Threshold is displayed under the Open Government Licence (HM Land Registry Price Paid Data, EPC Register, ONS, UK HPI). All figures produced by Threshold are statistical estimates for site appraisal, not RICS valuations.