What drives archaeological evaluation costs

Archaeological evaluation cost drivers are almost entirely set by other people. The curator decides how much of the site gets trenched. The ground decides how long the machine is on hire. What comes out of the trenches decides the specialist analysis bill. And the receiving museum decides what the archive costs to deposit. The developer's influence sits at the front end, in the desk-based work and the written scheme of investigation, and it shrinks rapidly once a machine arrives on site.

There is no published national fee schedule for this work, so any budget has to come from competitive quotations against an approved scope. What follows is the anatomy of that scope, so you can see which lines move and which do not.

How the curator sets the scope

For most sites the archaeological adviser to the local planning authority, usually a county archaeologist or an equivalent service, issues a brief setting out what evaluation is required and why. The contractor then writes a written scheme of investigation that responds to the brief, and the curator approves it. Work carried out without an approved scheme will generally not discharge the condition.

The brief is written from the historic environment record and from the desk-based assessment, so the quality of that assessment matters to the cost. A thorough Archaeological Desk-Based Assessment that establishes previous ground disturbance, existing basements, made ground depth and the results of nearby investigations can materially narrow the brief. A thin one invites a precautionary scope covering the whole site.

Engage before the condition is drafted where you can. Our note on written schemes of investigation for field evaluation covers what the document has to contain, and the difference between a scheme negotiated in advance and one imposed afterwards is usually the largest single saving available.

Trenching percentage and site area

Trial trenching is normally expressed as a percentage of the developable area, commonly in the range of 2 to 5 per cent, with the figure set by the curator according to the potential identified. Trenches are typically 1.8 metres wide, matching a standard machine bucket, in lengths of 20 to 50 metres.

Two consequences follow. Cost scales with site area rather than with the number of units, so a low density scheme on a large site carries a disproportionate evaluation cost relative to its value. And the percentage is negotiable in a way the area is not, particularly where geophysical survey has already mapped the anomalies and the trenches can be targeted rather than laid out on a grid.

Geophysical survey is the least costly intervention in the sequence on open greenfield land, and it earns its keep twice. It can reduce the trenching percentage by demonstrating where features are and are not, and it lets the trenches that do get dug answer a question rather than sample blindly. It is close to useless on urban brownfield sites with made ground, buried services and modern disturbance, so do not pay for it there.

Ground conditions and machine time

The excavator and its driver are on hire for the duration, and the variables that extend that duration are physical rather than archaeological.

The archaeological variable that does move the machine cost is feature density. A trench that turns out to be empty is closed quickly. A trench with intercutting ditches, pits and a possible structure needs hand excavation, recording and sampling, and a single productive trench can cost several times an empty one.

Specialist analysis after the fieldwork

The fieldwork invoice is rarely the largest one. What comes out of the ground generates a second phase of work, and it is the phase most often left out of a budget entirely.

Finds processing and assessment, then specialist reporting on pottery, metalwork, animal bone, worked stone and building material. Palaeoenvironmental assessment of bulk samples, then full analysis where the assessment shows potential. Scientific dating, which is charged per sample and where the number of samples is set by the research questions rather than by the developer. Human remains, which bring a separate legal requirement, since exhumation needs a licence from the Ministry of Justice and the conditions attached to it govern how the remains are treated and reburied.

The honest position is that this part of the cost cannot be fixed in advance. What you can do is require the contractor to price the assessment stage firmly and the analysis stage as a schedule of rates, so that the second phase is quantified against an agreed list rather than negotiated after the event.

Archive deposition and publication

Every project ends with an archive and a report, and both cost money after the site has been backfilled.

Deposition charges are usually levied per box or per unit volume by the receiving museum, and the figure varies widely. Some museums have restricted or closed to new deposits, which means the archive has to be held elsewhere or a different arrangement negotiated, and neither is free. Establish the receiving institution and its current charging position at written scheme stage, not at the end.

Reporting runs on two levels. A client report, deposited with the historic environment record and registered on the national index, is the minimum. Where the results are of wider interest, publication in a county or period journal, or a monograph for a large site, is normally expected and is written into the scheme. Budget the publication line separately, because it falls due long after the development has moved on and it is the item most likely to be forgotten.

Contingency for unexpected remains

Evaluation is a sampling exercise, and the point of it is to find out what is there. So the realistic outcomes include a result that triggers further work.

1. Nothing of interest, and the condition is discharged.
2. Limited remains, dealt with by a watching brief during groundworks.
3. Remains requiring targeted excavation of defined areas before construction.
4. Remains requiring full excavation of a large part of the site, which is a programme event rather than a cost line.
5. Remains of such importance that preservation in situ becomes the requirement, changing the foundation design.

Hold contingency against outcomes three and four, and hold it as programme float as well as money. An Archaeological Field Evaluation that finds something in January can push a groundworks start by a season, and the finance cost of that delay often exceeds the archaeology invoice.

Controlling the cost without cutting the scope

Five things work, and cutting corners on the scope is not one of them, because an inadequate evaluation gets repeated.

Commission the desk-based assessment properly and early, and use it to argue for a targeted rather than a blanket scope. Use geophysics on greenfield land to target trenches. Negotiate the written scheme of investigation rather than accepting a template, and get the trenching percentage, the analysis stage and the publication expectation defined in it. Obtain quotations from more than one organisation against the same approved scheme, and check registration status, which our note on registered organisation status explains. And design for preservation in situ where the remains allow, since a foundation redesign that avoids disturbance can cost less than excavating what lies beneath it.

On larger schemes, a planning performance agreement can bring the curator into the programme formally, which helps with sequencing and with fixing expectations about what the evaluation has to answer. Our note on planning performance agreements and when they pay sets out where that is worth doing.

Illustrative example. A 3 hectare greenfield site with a cropmark complex recorded nearby. Magnetometer survey across the whole area identifies anomalies across roughly a third of it. The curator agrees trenching targeted on the anomalous area plus a lower sampling rate elsewhere, rather than a uniform percentage across 3 hectares. Two of fourteen trenches are productive, and the assessment recommends targeted excavation of one enclosure before groundworks, with a watching brief elsewhere. The geophysics fee is a small fraction of the trenching it avoided. These stages and proportions are illustrative rather than drawn from a real project.

This is general guidance, not legal advice; check the position with your local planning authority's archaeological adviser or a qualified professional before relying on it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval. For specialist technical reports, qualified professional input may be required.

See PlanScope pricing if you want a fixed-cost draft desk-based assessment to take to the archaeological adviser.