What Is a Development Viability Appraisal?
A practical UK guide to development viability appraisals: GDV, costs, profit, residual land value, sensitivity and the evidence land teams should review.
5 min read
A development viability appraisal is a financial model used to test whether the value created by a proposed development is sufficient to cover the costs of delivering it, an appropriate developer return and the relevant land-value assumption. In practice, it brings together gross development value, build and infrastructure costs, professional fees, planning obligations, finance, programme and profit, then shows the resulting profit, deficit or residual land value.
That sounds like a calculation. The useful part is the decision it supports: should this site be pursued, renegotiated, redesigned, held for more evidence or rejected before the team spends much more time on it?
There is an important distinction at the outset. A commercial development appraisal used by a land or development team is not automatically the same thing as a formal viability assessment submitted in the planning process. Planning viability has its own policy context and recommended inputs. An internal appraisal may be earlier, faster and designed to support acquisition or investment decisions. The underlying financial logic overlaps, but the purpose and evidential standard can differ.
How This Works
A basic development appraisal starts with the proposed scheme.
First, estimate the gross development value, usually shortened to GDV. For residential development this may include private sales, affordable housing value and any other revenue generated by the scheme. For other uses, the valuation approach can differ.
Second, assemble the development costs. Depending on the site and level of detail, these can include:
base build costs
external works and infrastructure
abnormal costs
professional fees
contingency
Section 106 obligations
Community Infrastructure Levy
finance costs
marketing and sales costs
other site-specific delivery costs
Third, include the developer return or target profit. The right assumption depends on the purpose of the appraisal, the scheme and the evidence being used. It should not be treated as a universal percentage simply because it appeared in an old model.
Finally, decide what you want the model to solve for.
If the land price is known, the model can test the resulting profit or return.
If the land price is not known, the model can solve for residual land value: the amount left for the land after the other development costs and the target return have been allowed for.
For more complex projects, timing matters as much as totals. Receipts and costs happen at different points, so a cash flow and finance model can materially change the result.
Worked Example
Take a simplified residential scheme with:
GDV: £10.0 million
Development costs excluding land and target profit: £6.0 million
Target developer profit: £1.8 million
On that simplified basis:
£10.0m GDV
minus £6.0m development costs
minus £1.8m target profit
equals £2.2m residual land value
That does not mean the site is “worth £2.2m” in every sense.
The result is only as reliable as the assumptions underneath it. If sales values move, build costs rise, the affordable housing position changes, a major abnormal is discovered or the programme extends, the residual can move sharply.
That is why a useful appraisal does not stop at one answer. It shows the assumptions, the sources and the sensitivity of the result.
Review Method
A land or development team should be able to answer five questions before relying on the output.
1. Where did the GDV come from?
Use current, relevant evidence and make clear whether the inputs are site-specific, comparable-led, averaged or assumed.
2. Which costs are confirmed and which are allowances?
A build-cost benchmark is not the same thing as a cost plan. An abnormal-cost placeholder is not the same thing as a ground investigation.
3. What planning obligations have been allowed for?
Affordable housing, Section 106, CIL and infrastructure can materially change viability. The treatment should match the site and the applicable policy position.
4. What programme and finance assumptions are being used?
A model that gets the totals right but the timing wrong can still misstate the economics of a scheme.
5. What changes the decision?
Sensitivity analysis should focus on the variables capable of changing the acquisition or investment decision, not simply generate a decorative table.
A strong appraisal therefore records both the number and the evidence trail behind the number.
Sources Used
Homes England, Financial viability for housing-led projects:
https://www.gov.uk/guidance/financial-viability-for-housing-led-projects
GOV.UK, Planning Practice Guidance: Viability:
https://www.gov.uk/guidance/viability
RICS, Valuation of development property:
RICS Property Journal, residual land valuation method:
https://ww3.rics.org/uk/en/journals/property-journal/apc-5-valuation-methods.html
Limitations And Professional Review
A development appraisal is not a substitute for professional planning, valuation, cost, tax, legal, engineering or finance advice.
Early-stage appraisals often contain assumptions because the full evidence does not yet exist. That is acceptable if the assumptions are labelled, sourced where possible and revisited as the site progresses.
Residual outputs are particularly sensitive to small changes in inputs. Where a market valuation is required, the appropriate valuation standards and professional review should be applied. Where an appraisal is being used in the planning process, the current national and local viability requirements should be checked.
The aim of an early appraisal is not false precision. It is to make the next decision with the best evidence available and to show what still needs to be tested.
Where Harold Viability Fits
Harold Viability is designed to help land and development teams get from a new site to an inspectable first appraisal without rebuilding the same evidence across separate spreadsheets, PDFs and tabs.
The current appraisal workflow can bring the site record, planning evidence, development schedule, unit mix, GDV, affordable value, CIL, Section 106, build costs, external works, abnormals, professional fees, contingency, finance, target profit, residual land value, cash flow and sensitivity into one reviewable workflow.
The judgement still belongs to the team. The point is to spend less time assembling the first version and more time testing whether the assumptions are sensible.
If you want to see what that looks like on a real opportunity, send Harold one development site and review the appraisal rather than another generic demo.
For the wider land workflow beyond viability, see Harold Land:
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