Budgeting the archaeology contingency on a brownfield site

Archaeology on a brownfield site is not a line item you can price at appraisal. It is a range, and the width of that range narrows at three moments: when the desk assessment lands, when the evaluation results come in, and when the mitigation strategy is agreed with the archaeological adviser. Until the first of those, any number in your appraisal is a guess dressed up as a budget.

What you can do is control the shape of the exposure. Developers who lose money on archaeology usually do so because they discovered the scale of it after the land price was fixed, not because the archaeology itself was unusual.

Why it behaves like a contingency

The cost depends on what is in the ground, and nobody knows what is in the ground until somebody digs. That is the whole of it.

The work is normally secured by a condition requiring a written scheme of investigation to be approved before development begins, with the programme of archaeological work then carried out in accordance with that scheme. The condition fixes the process, not the price. A scheme that finds a single ditch and one that finds a cemetery run through the same condition wording.

Three cost tiers sit behind that condition. Desk assessment is small and certain. Evaluation is moderate and reasonably predictable, because it is defined by the area to be trenched. Mitigation is the tier that can move by an order of magnitude, and it is the only one that matters to a land appraisal.

What the desk assessment narrows

An Archaeological Desk-Based Assessment collects what is already known: Historic Environment Record entries, previous excavations nearby, historic mapping, geotechnical logs, aerial photography and any deposit modelling from adjoining schemes. It ends with a statement of archaeological potential and an assessment of survival.

On a brownfield site the survival question does most of the work. Deep basements, tank farms, made ground and modern piling can have removed the resource altogether across parts of a site, and an assessment that maps previous ground disturbance can reduce the area needing evaluation substantially.

Commission it before exchange where you can, and make it a condition of any option agreement where you cannot. It is the smallest sum in the whole process and it moves the widest range.

Evaluation and the decision it informs

Field evaluation usually means trial trenching, with a trenched sample of the developable area agreed with the archaeological adviser, commonly a few per cent, rising where potential is high. On constrained urban sites it may instead mean geoarchaeological boreholes or targeted test pits where trenching is impossible.

An Archaeological Field Evaluation has one purpose: to let the curator and the developer make an informed decision about mitigation. It is not an attempt to excavate the site.

Price it on a schedule of rates rather than a lump sum, with rates for machine hours, archaeologist days, environmental sampling and reporting. A lump sum tender for evaluation either carries a large risk premium or produces a variation claim, and neither helps.

The result of the evaluation is the number your appraisal has been waiting for. Until then, carry a contingency range in the appraisal and be explicit with the board about what would collapse it.

Mitigation options and their cost profile

Four broad outcomes, in ascending order of cost.

No further work, where evaluation shows the resource is absent or already destroyed. This is a real outcome on brownfield land and is more common than the anxious assume.

Preservation in situ, achieved by design change: raising slab levels, redesigning foundations, relocating attenuation or services. The archaeological cost is low, the design cost is not, and the decision has to be made early enough that the structural grid can still move.

Strip, map and sample, where topsoil and overburden are removed under archaeological supervision, features are recorded, and a proportion is excavated. Costs scale with area and with feature density.

Open area excavation, where the whole of a defined area is excavated and recorded before construction. This is the expensive outcome, and the cost scales with area, depth, feature density, waterlogging and the volume of finds.

A fifth possibility, rare but real, is that remains of national importance are identified. That can change the scheme rather than its budget, and it is the risk that argues for early evaluation on sites with known potential.

Post-excavation, archive and publication

The fieldwork ends and the invoices do not. Post-excavation assessment, specialist analysis of finds and environmental samples, conservation of unstable material, archive preparation and publication all follow, sometimes over two or three years.

Museums charge for accepting an archive, and some have closed to new deposits entirely, which creates its own problem for a developer whose condition requires deposition. Establish the receiving museum's position and its charges at the written scheme stage rather than at the end.

Publication obligations vary with the importance of the results. A short note in a county journal is one thing. A monograph is another. The written scheme should say which is anticipated and on what trigger it escalates.

Programme risk and how to price it

The cost risk is manageable. The programme risk is what damages a development appraisal, because finance charges accrue whether or not anyone is digging.

The items that extend programmes: mobilisation lead times for field units during the busy season, winter working in wet ground, dewatering where deposits are waterlogged, human remains requiring a licence for exhumation, finds reported under the Treasure Act 1996, and the agreement of a revised mitigation strategy after unexpected results.

Price programme risk in the same way as any other groundworks risk, with a dated risk register, an allowance per week of delay, and clear ownership of each item. The discipline is the same as budgeting for highway agreement costs in a development budget, where the sum is uncertain but the process is predictable.

Conditions that control the exposure

Negotiate the condition, not just the scheme. Pre-commencement conditions require the applicant's written agreement before they are imposed, which gives you a proper opportunity to discuss wording.

Four drafting points worth raising:

1. Phased discharge, so that work can start on parts of the site while archaeology continues elsewhere.
2. A defined trigger for each stage, tied to a physical operation rather than to "development" as a whole.
3. An explicit statement that the written scheme may be approved in parts.
4. Clarity about what constitutes completion of the archaeological work for the purpose of discharging the condition, including whether publication is caught.

That last point causes more disputes than any other. A condition requiring completion of the programme of archaeological work, including analysis and publication, before occupation is unworkable on a scheme with a two-year build. Raise it early, and agree wording that separates fieldwork from reporting obligations.

This is general guidance rather than legal advice, and archaeological requirements are set by individual authorities on the facts of each site, so check the position with your local planning authority or a qualified archaeologist before relying on it.

PlanScope drafts desk-based assessments and heritage documents structured to UK planning policy, with site-specific findings flagged rather than assumed, and pricing covers one free report, £50 per report, or Professional for unlimited reports. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.