Development appraisal software for UK residential schemes

A development appraisal answers one question: does this site work? Gross development value less every cost of building it, less the return the scheme has to make, leaves what you can afford to pay for the land. Get any input badly wrong and the answer is worse than no answer at all.

The chain

1. GDV — what the homes sell for. Median new-build prices by property type at local authority level, indexed forward to today.
2. Build cost — a rate per m² of gross internal area, adjusted by a regional location factor where the UK average is 100.
3. External works — roads, footways, drainage, attenuation, utilities, lighting, landscaping, fencing and parking.
4. Fees and finance — professional fees, sales and marketing, contingency, and interest over the build period.
5. Planning policy — affordable housing, the Community Infrastructure Levy, Section 106 contributions and biodiversity net gain.
6. Profit and the residual — the return the scheme must make, and whatever is left for the land.

Why measured externals matter

Externals are where spreadsheet appraisals go wrong. A percentage of build cost — 12% on a clean greenfield site, 18% on brownfield — is a reasonable placeholder, but it takes no account of the actual layout. A long, thin site with 600 m of adopted road costs far more per home than a compact one with 200 m, and no percentage will tell you that.

Because Airship has generated the layout, it can measure instead of assume: carriageway metres, footway area, plot and floor areas, fence runs, parking bays and open space all come off the drawing and are priced at a rate per unit.

Judging the answer

National planning practice guidance treats a return of 15 to 20% of gross development value as a suitable competitive return to a developer for the purposes of plan making. Airship rates schemes against that: below 10% is not feasible, 10–15% poor, 15–18% average, 18–22% good, above 22% excellent.

Every appraisal also shows what happens if values fall 5% while costs rise 5%. A scheme that only works in the favourable column does not work.

The inputs no dataset can supply

Two lines dominate the result and neither exists as national open data: the local affordable housing percentage and the CIL rate. Both come from the authority's own local plan and adopted charging schedule. A third — abnormals, meaning ground conditions, contamination and utility reinforcement — cannot be known without survey, and any one of them can exceed everything else in the model. Airship defaults abnormals to zero deliberately, and says so, rather than inventing a number.

From site to appraisal

Start by finding a site, generate a layout with the estate layout tools, then open the cost feasibility appraisal and export a four-page branded report for your lender or partner.

This is indicative feasibility software. It is not a valuation, not a viability assessment for submission to a planning authority, and not a substitute for advice from a RICS valuer, a quantity surveyor or a local agent.