I like Colin and have loved his vids earlier than. Cool man. I respect his engineering expertise. That is higher made than most small mines, though I am bemused by the inclusion of Kingspan which I do not see would do something in a secure thermal mass.
But when I used to be his neighbours, which he mentions are very shut, I might be fairly damned apprehensive about this. Mine workings collapse on a regular basis in Devon and Cornwall and typically take homes or lives with them.