What Inputs Do You Need for a Development Appraisal?
A practical checklist of the site, planning, value, cost, programme, finance and profit inputs needed for a development appraisal in the UK.
5 min read
A useful development appraisal needs seven groups of inputs: the site and proposed scheme, planning and policy assumptions, development values, build and site costs, planning obligations, programme and finance, and the target developer return. The important distinction is not simply whether every field is filled in. It is whether each material input is confirmed, evidenced or clearly labelled as an assumption.
At the first-pass stage, you will rarely know everything. You do not need to.
You do need enough to decide whether the site deserves more work and to understand which missing inputs could reverse that decision.
How This Works
A practical appraisal input checklist starts with the site itself.
Site Identity And Development Area
Record the full address or site reference, gross and net site area, boundary, local planning authority, current use and any obvious access or ownership issue.
Gross area alone can be misleading. A five-acre site with a large flood area, retained woodland, access constraint or infrastructure corridor may have a very different developable area.
Proposed Scheme
Record the working development schedule.
For residential development this can include:
number of units
tenure split
unit types and sizes
gross internal or external areas where relevant
private and affordable housing mix
density assumptions
non-residential floorspace if applicable
At early stage, this is often an indicative scheme rather than a design.
Planning And Policy
The appraisal should reflect the planning assumptions capable of changing value or cost.
These may include:
planning status
allocation status
relevant local-plan policy
affordable housing requirement
CIL
likely Section 106 obligations
major site constraints
planning history and relevant appeal evidence
infrastructure or phasing requirements
A financial model cannot rescue a planning assumption that was wrong at the start.
Development Value
For residential schemes, the key question is what the finished units are expected to sell for or otherwise be valued at.
Use relevant comparable evidence and record what has been adjusted for location, specification, size, tenure and timing.
Affordable housing value should be treated separately where applicable rather than assumed to behave like private GDV.
Development Costs
A first appraisal should normally distinguish between:
base build cost
external works
infrastructure
abnormal costs
professional fees
contingency
sales and marketing
planning and statutory costs
Section 106
CIL
finance
any other material site-specific cost
The reason to separate them is auditability. If “build cost” contains six different assumptions, the team cannot see which one has changed.
Programme And Finance
Timing affects finance and therefore viability.
Record the expected:
planning period
pre-construction period
construction programme
sales or exit period
phasing where relevant
debt assumptions
interest rates and fees
timing of equity and debt drawdown where the model requires it
A one-line finance percentage may be enough for a rough screen. It is not enough for every investment decision.
Target Return And Land Value
The appraisal needs a target return appropriate to the purpose of the exercise.
If the land price is known, test the return after land cost.
If the land price is unknown, solve for residual land value.
Do not hide the target return inside the model. It is a decision assumption and should be visible.
Worked Example
Imagine an agent sends a land team a brochure for a 3.8-acre residential opportunity.
The brochure gives an asking price and says “potential for circa 60 homes”.
That is enough to start a screen, but not enough to rely on a viability conclusion.
The team still needs to test:
whether 60 homes is a plausible development schedule
the net developable area
the affordable housing assumption
CIL and likely Section 106
local new-build sales evidence
build cost and abnormal allowances
programme and finance
target return
the resulting land-value position
The best early appraisal therefore does two things at once.
It produces a first answer from the evidence available, and it produces a list of the assumptions that matter enough to investigate next.
That is much more useful than pretending an incomplete appraisal is complete.
Review Method
For each input, record four things:
Source: where did the number or fact come from?
Date: when was that source current?
Status: confirmed, evidenced estimate or assumption?
Sensitivity: how much could this input move the decision?
Review the highest-sensitivity assumptions first.
For example, spending another hour refining a minor fee allowance is less useful if the unit count, sales values or abnormal cost position could still move the residual materially.
This is the practical purpose of an appraisal checklist: not completeness for its own sake, but prioritisation.
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:
Limitations And Professional Review
The right input set depends on the scheme and the decision being made.
A small early-stage residential site will not require the same modelling depth as a phased mixed-use development. A planning viability assessment has different requirements from an internal acquisition screen. A lender, valuer, developer and land promoter may also use the output for different purposes.
Do not treat an AI-generated or automated input as confirmed simply because it has been populated. The underlying source, date and assumption should remain inspectable.
Professional review is required wherever the decision depends on planning judgement, formal valuation, cost advice, legal title, tax, engineering, finance or other specialist work.
Where Harold Viability Fits
Harold Viability is built around the gap between “a site has arrived” and “the team has enough structured evidence to make the next decision”.
A team can start from a listing, brochure, plan or address, then review the extracted site information alongside planning evidence, comparables, costs, development assumptions and the financial model.
The objective is not to eliminate assumptions. It is to make them visible, reduce repeated data gathering and keep the source evidence next to the number the team is relying on.
The output should make it easier to say one of five things clearly: pursue, reject, reappraise, hold or proceed subject to named evidence.
Related reading once Article 1 is live:
What is a development viability appraisal?
For wider opportunity and land-workflow management:
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