Getting out of the ground

Cornwall’s rich mining heritage is one of the reasons we have our land. It is also a cause for concern when it comes to what’s hiding underneath. Fears of contaminated soil, mining features, mining spoil, undocumented offshoots of known/unknown mine shafts, and more.

Ground work
What lies beneath?

All of the above could negatively impact chances of getting a mortgage, and easily cost tens of thousands to fix. To better face and prepare for potential issues we arranged a full mining survey from Wheal Jane Consultancy. Our planning application included an environmental search that suggested the land was contaminant free. However, the search was merely a desktop search: ‘Computer says No’. The full mining survey included digging inspection pits horizontally and vertically through where the footings will go. Offering our first insight into how easy or hard it would be to get out of the ground. ‘Sadly’ this is when the wall came down. Our friendly mining consultant suggested it was unsafe, and needed to come down sooner rather than falling on someone’s head later.

The inspection trenches revealed no nasty surprises and good quality ground:  “Ideal for building”. With planning permission granted the ground work finally began. We’d been warned earth expands when taken out of the ground, and were fortunate in not needing to dig too far to find suitable ground for the footings. Even with this good fortune a small 300 tonnes of top soil had to be removed from the site.

Maen Karne

300 tonnes! The trucks kept coming. We hope they didn’t disrupt our neighbours and village too much. Maen Karne provided a very professional service, with friendly drivers. Their highly skilled drivers, mostly on turn around, managed to negotiate the drive and tight space on site with ease.

Trenches for footings

The footings / foundations are a standard affair:

  • 600-800mm deep trenches: mostly 600mm, and 750mm+ for our stone fronted walls
  • 225mm of concrete
  • 5 courses of tench block
  • Filled with hardcore: recycled 4 inch clean
  • 803 hardcore
  • Blinding sand in the garage with Damp Proof Membrane (DPM) before slab.
  • House is slab on top of 803. Then the DPM. Easier to do this way round and possible because of underfloor heating, and needing to have a 150mm difference between the finished floor height of the house and garage for building regs (potential fluid spills).

Only the drains caused Rich a minor headache. Tolerance for the drop from the furthest drain was tight, down to the last millimetres. Thankfully easily sorted by Rich.

Pretty standard foundations
Digging out lead to lots of discoveries: random pottery, medicine bottles and even a leather tap dancing shoe! Relics of generations passed. Nan is convinced the tap dancing shoe belonged to mother when she was a child. Digging the final tench Sam discovered a further ‘gift’ from the old bus depot, an inspection pit.
Old Bus Depot Inspection Pit
We’re enjoying the continuation of the inspection pit forming part of our garage’s foundations. We’d hoped to be able to use the pit but closer inspection revealed it to be poorly built. Scary to think people worked under heavy busses in it! £400 worth of additional concrete appeased the building inspector. The only additional cost suffered in getting out of the ground.
Once out of the ground we all breathed a sigh of relief. Each completed phase reduces our risks and stress levels: Land ownership > planning approval > mortgage approval > out of the ground >… Greatly looking forward to the roof being on and windows in.
Happy to answer any questions in the comments.
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