Checking coal mining risk before you design foundations

Before you settle on strip footings, find out whether your plot sits inside a Development High Risk Area. If it does, the planning application will need a coal mining risk assessment, the mining authority becomes a consultee, and the foundation solution may change from trench fill to a raft or piles. That check takes about ten minutes online and it is free.

The body that holds the records is the Coal Authority, now operating as the Mining Remediation Authority. It keeps the national record of coal mine entries, recorded and probable shallow workings, mine gas, surface hazards and tips across the English, Welsh and Scottish coalfields. Its interactive map is the starting point, and for a self builder it is one of the highest value free checks available.

Where coalfield referral areas apply

Coal was worked over a much wider area than most people assume. The obvious coalfields are Nottinghamshire and Derbyshire, South Yorkshire, County Durham and Northumberland, Lancashire, Staffordshire, Warwickshire, Leicestershire, Kent, the Forest of Dean, Somerset, and South and North Wales. Shallow and early workings extend beyond the deep mining areas into places with no mining in living memory.

The authority defines Development High Risk Areas covering roughly a sixth of the coalfield footprint. Inside those areas, applications are referred and standing advice applies. Outside them, but still inside a coalfield, the risk is lower but not zero, and a purchaser's mining search is still sensible.

Two different products get confused here:

• the free interactive map, which shows whether your site is in a Development High Risk Area and flags recorded features
• a paid coal mining report, which is a property specific search used in conveyancing and lending

The map answers the planning question. The report answers the purchase question. On a self build plot you usually want both, at different stages.

Using the interactive map

Search by postcode or drag to your plot, then switch on the layers. What you are looking for, in order of consequence:

1. Mine entries, shown as shafts and adits with a location accuracy that is often poor for pre 1872 features.
2. Recorded shallow coal workings, where seams were worked at depths that can still affect the surface.
3. Probable shallow workings, inferred from seam outcrop and geology rather than from a plan.
4. Surface hazards, tips and areas of past opencast working.
5. Mine gas features and any coal authority remediation history.

Take a screenshot with the plot boundary visible and the date on it. That image goes into your desk study, and it is the evidence the case officer looks for first.

Accuracy deserves a warning. A shaft plotted at a point on the map may sit tens of metres from that point, because many entries were recorded long after they were abandoned and some were never recorded at all. Treat a plotted shaft as a search area, not a coordinate.

What triggers the consultation

Being inside a Development High Risk Area is the trigger. The application then needs a coal mining risk assessment as a supporting document, and authorities in coalfield districts list it on their local validation checklist. Submit without it and the application is likely to be made invalid, which costs you the determination clock rather than the fee.

The assessment is a desk based report by a suitably experienced geotechnical or engineering geology practitioner. It reviews the authority's data, historic Ordnance Survey mapping, borehole records, the published geology and any previous ground investigation, then reaches a conclusion on whether coal mining legacy features could affect the stability or safety of the proposed development, and what further work is needed.

PlanScope does not produce coal mining risk assessments. It is not one of the 66 report types. The desk study material overlaps heavily with a Land Contamination Phase 1 report and a Geotechnical Assessment, both of which PlanScope does draft, so the historic mapping and site history work can be shared rather than paid for twice.

Shafts, adits and shallow workings

Each feature has a different consequence for design.

A mine entry within or close to the site usually means locating it precisely by trial trenching or probing, then treating it: excavating and capping with a reinforced concrete slab designed to bridge the shaft, with a stand off recorded on the layout. Authorities normally secure a no build zone around a treated entry by condition.

Recorded shallow workings mean the ground beneath may contain voids. Typical treatment is drilling and grouting on a grid, or a raft foundation designed to span potential subsidence, or dynamic probing to confirm the workings have collapsed and consolidated.

Probable shallow workings mean nobody knows. That is the case that most often leads to an intrusive investigation, because the cheapest way out of uncertainty is a few boreholes.

Mine gas, principally carbon dioxide and methane, is a separate question and leads to gas monitoring and, where needed, a gas protection design following the published standards on characterisation and protective measures.

The permit nobody expects

Drilling into or disturbing coal, including grouting works and boreholes that pass through a seam, needs the authority's written permission, because the coal itself remains vested in the authority under the Coal Industry Act 1994. Your ground investigation contractor should handle the application, but it takes time and it is a genuine programme item. Starting intrusive work in coal without permission is not a planning breach, it is a separate legal problem.

Programme and cost consequences

Honest version: finding nothing takes ten minutes and costs nothing. Finding a probable shallow working costs you a desk assessment, then a ground investigation, then possibly a treatment scheme, and it can add two to three months to a self build programme if you discover it after you have submitted.

Sequence that avoids the worst of it:

1. Check the interactive map before you exchange contracts.
2. If the site is in a Development High Risk Area, commission the risk assessment during design, not after.
3. Combine the mining desk study with the contamination desk study and the geology review in one instruction.
4. Programme any intrusive investigation to give results before you fix the foundation design.
5. Expect a condition requiring the recommendations of the assessment to be implemented, and a further condition requiring a verification report.

Where a shaft is confirmed, the design response is usually to move the building rather than treat the shaft, if the plot allows it. Treatment is expensive and the residual stand off constrains the layout anyway.

Limits of relying on the data

The record is incomplete by design. Plans were not required before the second half of the nineteenth century, small scale bell pits and day holes went unrecorded, and abandonment plans were sometimes lost. The authority's data tells you what is known, not what is there. A site that shows clear on the map can still contain a forgotten entry, which is why the risk assessment reasons from geology and seam outcrop as well as from the plotted features.

That is also why the assessment should not simply repeat the map. A report that says the site is in a high risk area and recommends an investigation, with no interpretation of the seams, their depth and their likely condition, gets a holding response from the consultee.

If you are still at the site selection stage, the same viewer answers a different question, and the coalfield check before you buy explains how to read it for purchase risk. Once you have the constraint list, a single site constraints plan built from open data keeps the mining, flood and ecology layers in one place.

Enter your postcode on PlanScope to see which of the 66 report types your plot is likely to need, then commission the specialist work with the desk study already drafted.

PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval. Coal mining risk work needs a suitably qualified and experienced practitioner, and this is general guidance rather than legal advice.