What Is a Land Viability Toolkit? A Guide for Social Housing Developers

What is land viability?

Land viability is the assessment of whether a site can be delivered as a viable scheme: one that generates enough value to cover development costs, pay a reasonable price for land, meet the planning authority's affordable housing requirements and, for a housing association, deliver the financial outcomes its business plan and grant commitments require.

It sits where planning policy, development economics and housing finance meet. A site that works for a private developer building homes for sale may not work for a housing association delivering a mainly affordable scheme. A site that is unviable at a planning authority's affordable housing requirement may become viable with grant or a different tenure mix.

The planning framework

The National Planning Policy Framework expects development that complies with up-to-date plan policies to be assumed viable. Policy DM5 limits site-specific viability assessments to particular circumstances, such as a development materially different from those tested when the plan was made, or costs the plan's viability evidence did not account for. Any assessment submitted must fully evidence its inputs, follow the approach in planning practice guidance including its standardised inputs, and be made publicly available. The price paid for land cannot justify failing to meet plan policies (NPPF, August 2026, policy DM5).

Planning practice guidance sets the benchmark for land value: existing use value plus a premium for the landowner, often called EUV+, rather than the price paid (Planning Practice Guidance: Viability). A residual land value below the benchmark indicates a viability gap.

The purpose of a land viability toolkit is to let a development team test all this quickly and reliably, across a range of scenarios, from first site identification through Section 106 negotiation to board approval.

What a land viability toolkit should contain

A development appraisal model

The core is an appraisal model that calculates residual land value, return and scheme viability under different assumptions. For social housing developers it must handle mixed-tenure schemes, including Social Rent, Affordable Rent, shared ownership and market sale, in one appraisal, with results for each tenure.

ProVal handles multiple tenures in a single appraisal and reports NPV, IRR and payback. A custom Excel model can do the same, but field audits find errors in most operational spreadsheets, and a bespoke model's maintenance burden grows as schemes become more complex and the programme scales.

Sensitivity scenarios

A viability assessment is only as useful as the scenarios it tests. The toolkit should cover the variables that most affect affordable housing viability: build cost, sales values, interest rates, programme delay, grant levels and the affordable housing percentage. These should run quickly, without rebuilding the appraisal for each test, and on consistent organisation-wide assumptions. ProVal lets teams stress-test grant, build cost and sales price and see where the viability threshold sits, and lets administrators set assumptions and defaults centrally.

Grant and subsidy modelling

For housing associations, viability often depends on grant. The toolkit should model grant under Homes England's Social and Affordable Homes Programme 2026 to 2036, legacy Affordable Homes Programme schemes and Recycled Capital Grant Fund balances (Capital Funding Guide, chapter 6). It should also show what is viable at different grant levels, including without grant.

Residual land value against the benchmark

Section 106 viability negotiations turn on the relationship between a scheme's residual land value and the site's benchmark land value. The toolkit should produce residual land value calculations whose inputs are fully evidenced, as the NPPF requires, in a form a planning authority's assessor can review and that can be published.

Reporting for each audience

Viability work goes to investment committees, boards, funders, planning authorities and lenders. The toolkit should include, or connect to, reporting formats for each. Proval provides standard reports and exports to CSV, Excel, PDF and HTML, and SDS offers custom reports as a separate service.

Landval Edge: land valuation before full appraisal

Landval Edge is SDS's cloud-based land valuation software, used by registered providers, local authorities and private developers to appraise sites before committing to acquisition. It models residual land value, build costs and scheme viability in one place.

According to the product page, Landval Edge:

• models residual land value against multiple scheme layouts and unit mixes on the same site, without rebuilding the model for each option;
• builds in current build cost, grant and sales assumptions;
• flags viability gaps before an offer is submitted;
• produces a shareable output for internal or board sign-off;
• manages roles, permissions and stamp duty settings centrally.

For registered providers and local authorities it calculates residual land value; for private developers it targets a user-specified profit margin, using the same underlying model. It can also appraise acquisitions of existing stock.

Landval's output is designed to feed into Proval for full appraisal. At present the handoff is manual; SDS has said direct integration is on the way.

Building a consistent toolkit across the organisation

A toolkit built on bespoke spreadsheets or informal processes tends towards inconsistency. Development managers apply different cost assumptions, sensitivity tests and report formats, so when schemes reach committee they are compared on different foundations.

A purpose-built platform builds consistency in. Every appraisal uses the same structure, calculation logic and report formats, and organisation-wide defaults replace individual choices. SDS Proval stores appraisals centrally, with one version of each scheme, user permissions, and assumptions, defaults and overrides held in one place. Users can also see real-time audit information on activity. That consistency gives boards confidence that schemes are compared on the same basis, and it gives auditors a clear record.

Connecting the toolkit to project management

Viability assessment continues after land acquisition. As a scheme moves through planning, procurement and construction, its original assumptions meet reality: build costs change, programmes extend, and grant allocations are confirmed or adjusted. The approved appraisal is the baseline that delivery should be measured against.

Proval passes approved figures into Sequel, SDS's project management software, as each scheme's baseline budget and milestones. Sequel flags variance against the approved appraisal as scheme data is updated, so a team can see costs running ahead of the viability case while there is still time to respond.