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The cost feasibility appraisal

The Cost Feasibility appraisal prices the layout you actually generated. Road centreline metres, footway area, plot and floor areas, open space, fencing and parking are all measured off the drawing, not assumed from a rate per acre.

Opening it

📊 Cost feasibility… in Development & costs. A summary — the rating, GDV, total cost, profit and land — also appears in Site information & stats, so you can see where a scheme stands without opening anything.

Sales values

Set a price per home for each house type, or press ↻ Fetch to pull local evidence. Airship takes ONS median new-build prices by property type for the local authority and indexes them forward on HM Land Registry’s new-build house price index.

Expect ±15–20% at district level, and more where few comparable new homes have sold. Where an authority has too few sales to publish a median, Airship says so rather than guessing.

Build cost

A rate per m² of gross internal area for each house type, adjusted by a regional location factor where the UK average is 100 — so 93 means 7% below the national average. Fetch sets the factor from the site’s region.

The factor is an index, not a multiplier. Enter 93, not 0.93.

Terraces: ends and mids

Where a scheme has terraces or semis, each house type splits into separate lines by its position in the run — Mews 2B3P — mid-terrace and Mews 2B3P — end of terrace — with their own sales value and their own build rate. They are genuinely different products: an end carries an extra external wall over two storeys plus a return gable, so it costs more to build and sells for more.

A pair of semis is priced on the semi-detached rate, which already assumes one shared wall.

On the value side you also get an end-of-terrace premium — a multiplier on the terraced value, about 5% by default and editable. It appears only when the scheme actually contains ends, and it is applied when you ↻ Fetch local evidence.

Why a premium rather than its own figure? ONS publishes medians for four property types — detached, semi-detached, terraced and flats. There is no published end-of-terrace median to fetch, so Airship starts from the terraced figure and adds a premium you control, rather than inventing a band.

Check the new lines have values. The first time a scheme gains a terrace, the end and mid lines start from whatever that type was already worth. If a line shows no value, the appraisal says so explicitly and names it — those homes would otherwise be priced at nothing.

External works

Two methods, and only one applies at a time:

Measured — quantity × rate against your actual layout: carriageway, kerbs, footways, drainage, attenuation, utilities, street lighting, landscaping, trees, fencing, parking, site clearance and topsoil. This is the one that uses the geometry.
Percentage of build cost — 12% is typical on a greenfield estate, 18% on brownfield. Useful before the layout is settled.

Planning policy

Four levers, each editable per site and each explaining where its number came from:

Affordable housing — 35% in London, 30% elsewhere as an NPPF starting point. Your authority’s local plan is the figure that binds.
CIL — Airship checks the national register and tells you whether the authority has an adopted charging schedule, linking the PDF. Rates are not published as data, so you enter the residential rate.
Section 106 — a national build-up of education, highways, open space, health, community and monitoring. Real figures range from near zero to over £30,000 a home, and should taper where CIL is charged.
Biodiversity net gain — a placeholder. Sites of 0.2 ha or less are exempt. The real cost is driven by the baseline habitat survey, which is field data.

These two are the biggest swings in the model — the affordable percentage and the CIL rate — and neither exists as national open data. Check the local plan and the adopted charging schedule.

Major development

Affordable housing and M4(2) accessible dwellings only apply to major development, which Airship works out from your scheme: 10 or more homes, or a site of 0.5 ha or more. You can override it.

Land, profit and the rating

Two modes. I know the land price computes the profit your scheme would make. Solve for land value works backwards to the most you could pay and still hit your target return — in that mode profit is an input, so the residual is the answer, and a residual at or below zero means the scheme cannot carry any land cost at all.

Rating	Profit on GDV
Not feasible	below 10%
Poor	10 – 15%
Average	15 – 18%
Good	18 – 22%
Excellent	above 22%

The bands follow national planning practice guidance, which treats 15–20% of gross development value as a suitable return to a developer for plan making.

Sensitivity

Every appraisal shows what happens if values fall 5% while costs rise 5%, and the reverse. If a scheme only works in the favourable column, it does not work.

Abnormals default to zero. Ground conditions, contamination and utility reinforcement cannot be known from any dataset, and any one of them can exceed everything else in the model. Enter them deliberately.

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