Planning viability sits at the intersection of planning law, development economics, and property valuation. It is a battleground between developers (who argue that affordable housing requirements and infrastructure contributions are too high) and local authorities (who argue that contributions are essential to fund public infrastructure and create mixed communities). NPPF paragraph 57 requires viability assessments to be based on the standardised NPPG methodology — but in practice, viability disputes regularly end up at the Planning Inspectorate on appeal, with inspectors making their own assessment of the appropriate benchmark land value and developer's profit margin. For landlords involved in residential development, conversion, or change of use schemes, understanding the viability framework is essential to negotiating proportionate planning obligations.
NPPF Viability and the National Planning Practice Guidance Framework
The National Planning Policy Framework (NPPF, updated 2023) sets the overarching context for viability in planning: (a) NPPF paragraph 57: where up-to-date policies have set out the contributions expected from development, planning applications that comply with those policies should be assumed to be viable; it is up to the applicant to demonstrate whether particular circumstances justify the need for a viability assessment at the application stage; (b) NPPF paragraph 58: the costs and value of development will vary, and any development plan policies on infrastructure and affordable housing contributions should provide sufficient flexibility to adapt to changing economic circumstances; (c) The NPPG on viability (updated 2019): the National Planning Practice Guidance on viability sets out a standardised approach to viability assessment; key elements include: (i) the residual land value (RLV) method — calculating the maximum a developer could pay for land after deducting all costs and a reasonable profit from the expected gross development value (GDV); (ii) the benchmark land value (BLV) — the minimum price the landowner would accept (based on existing use value plus an appropriate premium to incentivise the release of the land for development); (iii) comparison of RLV to BLV — where RLV exceeds BLV, the development is viable at the proposed level of obligations; where RLV falls below BLV, the obligations must be reduced to make the development viable; (d) Publication requirement: viability assessments submitted in support of planning applications should be publicly available for scrutiny; commercially sensitive information may be redacted in limited circumstances — Harman J in Parkhurst Road Ltd v Secretary of State [2018] confirmed the principle of openness; (e) 'Policy-compliant' as the starting point: the NPPG establishes that the starting point for any viability assessment should be full policy compliance — the developer must demonstrate why full compliance is not viable, not why reduced contributions are preferable.
- NPPF para 57: policy-compliant applications presumed viable; viability assessment only required where specific circumstances justify it
- NPPF para 58: policies should be flexible to adapt to changing economic circumstances; viability is a dynamic test
- NPPG standardised methodology: RLV (residual land value) compared to BLV (benchmark land value); RLV > BLV = viable; RLV < BLV = obligations must be reduced
- Publication requirement: viability assessments must be publicly available for scrutiny; Parkhurst Road [2018] confirmed the principle of openness
- Starting point = full policy compliance: developer must demonstrate unviability, not merely that reduced contributions are preferable
The Residual Appraisal — GDV, Costs, Developer Profit, and Benchmark Land Value
The residual appraisal is the core financial model used in viability assessments. It works as follows: (a) Gross Development Value (GDV): the total expected revenue from the completed development — sales receipts for market homes; capitalised rental income for build-to-rent; affordable housing land transfer values; commercial unit values; the GDV is typically calculated using comparable market evidence adjusted to the anticipated completion date; (b) Total development costs: (i) build costs — based on RICS Build Cost Information Service (BCIS) rates adjusted for location, design, and specification; (ii) professional fees — architect, structural engineer, project manager, planning consultant (typically 10-15% of build costs); (iii) finance costs — interest on the land purchase and build costs during the development period (typically at a rate of 6-8%); (iv) marketing and sale costs (1-3% of GDV); (v) developer's overhead and on-costs; (vi) abnormal costs — ground remediation; archaeological; flood mitigation; site-specific constraints; (c) Developer's profit: the profit margin that a reasonable developer would require to take on the risk of the development; NPPG guidance states that 15-20% profit on GDV is typical for private market housing; 6% on cost is typically used for affordable housing; development economics practice varies, and inspectors scrutinise the profit assumption carefully; (d) Residual Land Value (RLV) = GDV minus (all costs plus developer's profit); (e) Benchmark Land Value (BLV): the BLV represents the minimum price the landowner would accept to release the land; the NPPG BLV methodology: (i) existing use value (EUV) — the value of the land in its existing use before development; (ii) plus a reasonable landowner premium — the additional return required to incentivise the landowner to sell (typically 10-20% above EUV in NPPG guidance; often higher in disputed cases); (f) Viability outcome: if RLV > BLV, the development is viable at the proposed obligation level; if RLV < BLV, the obligations must be reduced (or deferred via a review mechanism) to achieve viability.
- GDV: total expected sales revenue or capitalised income from the completed development; the starting point for any residual appraisal
- Build costs: BCIS-based rates adjusted for location and specification; developer will argue upward adjustments for abnormal costs
- Developer profit: 15-20% on GDV for market housing (NPPG guidance); inspectors scrutinise profit assumptions — using a higher margin reduces the apparent RLV
- BLV = EUV plus landowner premium: existing use value plus incentive premium (10-20% per NPPG, often more in practice); LPA will argue a lower BLV to maximise obligations
- RLV vs BLV: if RLV exceeds BLV the scheme is viable; if RLV falls below BLV the obligations must be reduced to restore viability
Section 106 Obligations and Viability Negotiation
Section 106 of the Town and Country Planning Act 1990 allows an LPA to enter into planning obligations with a developer to secure contributions towards: affordable housing (on-site provision or off-site financial contributions); highway improvements; public open space; education; healthcare; biodiversity net gain mitigation; and other infrastructure identified in the Local Plan. The interaction with viability: (a) Affordable housing requirements: Local Plans typically require affordable housing contributions on residential developments above a certain threshold (usually 10+ units); the policy requirement (e.g. 30% of units as affordable) is tested against viability; where the full policy requirement is unviable, the LPA can accept a reduced percentage; the LPA should not refuse planning permission solely because a developer cannot meet the full affordable housing policy — the NPPG acknowledges that the policy requirement may sometimes need to be reduced; (b) Viability review mechanisms: where a viability assessment at the time of the application shows limited or no viability, a planning obligation can include a viability review mechanism — a clause requiring the developer to share any profit uplift (above the assumed developer profit) with the LPA as additional affordable housing contribution; typical review triggers: on grant of planning permission; on implementation; at a defined point in the development programme (e.g. practical completion of Phase 1); (c) Section 106A/B modification and discharge: where market conditions change after the s.106 obligation is agreed (and the development becomes unviable at the agreed obligation level), the developer can apply under s.106A to have the obligation discharged or modified; where the LPA refuses to modify, the developer can appeal to the Planning Inspectorate under s.106B; the Inspector will assess viability at the time of the application for modification; (d) Off-site financial contributions: where on-site affordable housing is impractical (e.g. small sites; specialist housing types), the LPA may accept an off-site financial contribution equivalent to the affordable housing value foregone; the contribution is calculated on the basis of the subsidy required to make the affordable units viable for a registered provider to acquire.
- Affordable housing policy threshold: Local Plans set percentage requirements (typically 20-40%); viability testing can reduce the requirement on specific sites
- Viability review mechanism: clause in the s.106 obligation triggering a profit-share review at key milestones; used where viability is marginal at the time of planning permission
- s.106A modification: developer can apply to vary a s.106 obligation if market conditions have changed and the scheme is now unviable at the agreed level
- s.106B appeal: where LPA refuses s.106A modification, the developer can appeal to the Planning Inspectorate for an independent viability review
- Off-site financial contribution: accepted where on-site provision is impractical; calculated on the subsidy required for a registered provider to acquire affordable units
CIL Exemptions, the Housing Delivery Test, and Appeal Viability
Two further aspects of the viability framework are important for developers: (a) Community Infrastructure Levy (CIL) exemptions and relief: CIL is a charge set by LPAs on new development, payable at rates set in the CIL charging schedule; CIL is payable on the commencement of development and cannot be deferred in the same way as s.106 contributions; however, exemptions are available: (i) self-build exemption: residential extensions (up to 100 sq m of new floor space) and self-build homes are CIL-exempt; the exemption must be claimed before development commences; (ii) social housing relief: affordable housing (including social rent, affordable rent, and shared ownership) is CIL-exempt where it meets the definition in the CIL Regulations 2010; the housing association or registered provider must claim the relief before commencement; (iii) exceptional circumstances relief: where the CIL charge itself (in addition to other obligations) renders the development unviable, the developer can apply to the LPA for exceptional circumstances relief; the LPA must be satisfied that: the hardship is exceptional; granting relief will not undermine the LPA's ability to fund its infrastructure; (iv) charity relief: charities developing land for charitable purposes are CIL-exempt; (b) The Housing Delivery Test (HDT): the HDT (introduced in 2018) measures whether LPAs have delivered sufficient housing against their annual housing requirement over the preceding 3 years; where an LPA delivers below 95% of its target, it must apply a buffer to its 5-year housing land supply; where delivery falls below 75%, the presumption in favour of sustainable development is triggered; where delivery falls below 25%, a 20% buffer is applied to the 5-year supply figure; LPAs with poor HDT scores find it harder to resist planning appeals for housing development; (c) Viability on appeal: where a developer is refused planning permission (partly because of an inability to meet affordable housing policy requirements), the Planning Inspectorate on appeal conducts its own viability assessment; inspectors use the NPPG standardised methodology; the inspector's determination of the BLV and developer profit margin is critical — different assumptions can significantly change the viability outcome; instructing expert witnesses (development economists; surveyors with development viability expertise) for appeals is standard practice in contested viability cases.
- CIL self-build exemption: residential extensions up to 100 sq m and self-build homes are CIL-exempt; claim before development commences
- Social housing CIL relief: affordable housing (social rent; affordable rent; shared ownership) is CIL-exempt; housing association must claim before commencement
- Exceptional circumstances CIL relief: available where the CIL charge renders development unviable; LPA must be satisfied that relief will not undermine infrastructure funding
- Housing Delivery Test: LPAs delivering below 75% of housing target face the presumption in favour of sustainable development; below 25% triggers a 20% land supply buffer
- Appeal viability: Planning Inspectorate conducts independent NPPG-based viability assessment on appeal; BLV and profit margin assumptions are the key variables in contested cases
Frequently asked questions
What is a viability assessment and when do I need one?+
A viability assessment is a financial appraisal that demonstrates whether a proposed development can viably support the affordable housing and infrastructure contributions required by the Local Plan. Under NPPF paragraph 57, where an application complies with up-to-date planning policy, it is presumed viable and a viability assessment is not required. You only need a viability assessment where you are seeking to provide less than the policy-required level of affordable housing or other contributions — and you must demonstrate why full compliance is financially unviable.
How is the benchmark land value calculated?+
The benchmark land value (BLV) is calculated under the NPPG methodology as the existing use value (EUV) of the land plus a reasonable premium to incentivise the landowner to sell. NPPG guidance suggests the premium is typically 10-20% above EUV — though in practice, disagreements between developer and LPA viability experts on the BLV are one of the most common sources of viability dispute. A higher BLV makes it easier for the developer to demonstrate unviability (because the RLV is more likely to fall below it); the LPA will argue for a lower BLV.
Can I reduce the affordable housing requirement through a viability assessment?+
Yes, if you can demonstrate that providing the full policy-level affordable housing makes the development financially unviable. NPPG requires the LPA to consider viability evidence and to accept a reduced affordable housing requirement (or phased delivery) where full compliance would make the scheme unviable. The starting point is always the full policy requirement; you must demonstrate that the reduction is necessary, not merely preferable. The LPA may insist on a viability review mechanism — a profit-share clause triggered if the scheme performs better than projected.
What is the Housing Delivery Test and how does it affect planning applications?+
The Housing Delivery Test (HDT) measures whether a local planning authority has delivered sufficient homes against its housing target over the preceding 3 years. Where an LPA delivers less than 75% of its target, the presumption in favour of sustainable development is triggered for planning applications — making it easier for developers to obtain planning permission for housing. Where delivery is below 25%, a 20% buffer is added to the 5-year housing land supply requirement. LPAs with poor HDT scores are more vulnerable to speculative housing appeals.
Can I challenge a Section 106 obligation if the market has changed?+
Yes, under TCPA 1990 s.106A. A developer can apply to the LPA to modify or discharge a planning obligation where it has become outdated due to changed market conditions. The application must demonstrate that the obligation no longer serves a planning purpose (or that its effect is no longer necessary). If the LPA refuses to modify the obligation, the developer can appeal to the Planning Inspectorate under s.106B. The inspector will assess viability at the time of the s.106A application — not at the time the original obligation was agreed.