Cornwall has been mined for tin, copper and other metals for centuries, and the remains of that industry are everywhere, from engine houses on the cliffs to shafts hidden under fields and gardens. Much of this landscape is now part of the Cornwall and West Devon Mining Landscape World Heritage Site. For anyone buying a plot, planning a new build or adding an extension, that history matters, because old workings can affect the ground you build on. This guide explains the checks involved and how they fit into a building project.
Why mining history matters when you build
Most homes in Cornwall are never affected by mining. But where old workings are close to the surface, they can cause problems if they're not identified and dealt with:
Mine shafts were often capped with timber or simply backfilled, and these covers can decay or the fill can settle over time.
Shallow workings and adits (horizontal tunnels) can leave voids under the ground.
Spoil and waste heaps can be loose and variable, and may contain contaminants.
Records are incomplete. Many older workings were never recorded accurately, so a lack of records doesn't always mean a lack of risk.
That's why the checks below are routine for many Cornish building projects, especially in the traditional mining districts around Camborne, Redruth, St Day, St Agnes, Wendron, St Just and Caradon, though workings exist in many other areas too.
What is a Cornwall mining search?
A mining search is a desk-based report on known mining activity near a property or plot. In Cornwall it's different from a standard Coal Authority search, which mainly covers coal. A Cornish search draws on historic mine plans, maps and records of metalliferous mining and china clay working.
A search will usually tell you whether there are recorded shafts, adits or workings on or near the site, and whether further investigation is recommended. Conveyancing solicitors often order one as part of buying a property in Cornwall, and it's a sensible step before buying a building plot. If you already own the land, it's still worth having one before the design stage.
When further investigation is needed
If a search or a site walkover suggests there could be workings nearby, a structural or geotechnical engineer may recommend a ground investigation. Depending on the site, this can include:
A more detailed desk study of historic plans and aerial photographs.
Trial pits dug with an excavator to look at the ground directly.
Probe drilling to check for voids at depth.
Locating and assessing a shaft so its position and condition are understood.
Where a shaft is found, it's usually dealt with to an engineer's design, often by filling it and installing a reinforced concrete cap, and sometimes by adjusting the layout of the building to avoid it. This work should only ever be carried out by competent contractors under professional supervision, because open or collapsing shafts are genuinely dangerous.
The results feed into the foundation design. On straightforward sites, standard foundations may be fine. On more complex sites, the engineer may specify deeper or reinforced foundations. Our groundworks and foundations page and our guide to groundworks in Cornwall explain how this stage works.
Contamination from mining waste
Mining has left raised levels of naturally occurring metals such as arsenic in the soil in some parts of Cornwall. On sites near old mine waste, Cornwall Council may ask for a contaminated land assessment as part of a planning application for a new home, particularly where there will be gardens. If contamination is found, the usual approach is a remediation plan, which can include removing affected soil or capping garden areas with clean material. The aim is to make sure the site is suitable for its proposed use.
Radon in Cornwall
Radon is a naturally occurring radioactive gas that comes from the granite and other rocks found across much of Cornwall. The UK Health Security Agency publishes radon maps, and Building Regulations require radon protection in new homes and extensions in affected areas. Depending on the level of risk, this can range from a gas-resistant membrane to a membrane plus a sump or ventilation system beneath the floor. Our guide to Building Regulations in Cornwall covers the approval process.
How this fits into your project
Ground checks are best done early, ideally before you buy a plot and certainly before detailed design. A typical order is:
Mining search during purchase or at the very start of the project.
Site walkover and engineer's review if anything is flagged.
Ground investigation, if recommended, before foundations are designed.
Planning conditions relating to ground or contamination dealt with as required.
Building Control inspections of foundations and radon protection during the build.
Leaving these steps until work has started can lead to delays and redesign, so it's worth building them into the programme and budget from day one. If you're planning a new build, a self-build home or a home extension, we can work alongside your engineer to keep things moving. Our project management and QS services can help coordinate the specialists involved.
Mining land FAQs
Is a mining search the same as a Coal Authority search?
No. A Coal Authority search mainly covers coal mining. In Cornwall, a mining search covering metalliferous mining and china clay working is usually more relevant.
Can you build on a site with a mine shaft?
Often, yes, once the shaft has been located, assessed and made safe to an engineer's design, and the building designed around it. Each site is different, so professional advice is essential.
Do extensions need radon protection?
In affected areas, Building Regulations can require radon protection in extensions as well as new homes. Your designer or Building Control can confirm what's needed for your address.
Who arranges ground investigations?
Usually your structural or geotechnical engineer specifies them, and they're carried out by specialist contractors. We can help coordinate this as part of the wider project.
Talk to us about your project
If you're planning to build on a plot or extend a home anywhere in Cornwall and want to understand the ground first, call Cornish Building Company on 01208 816991 or contact us to talk through your plans.
