Void under oiltank raft

Done / left deliberately in case have to get to main "4inch" soil-pipe?

Size of this space?

Raft is 960mm wide, and get then on probing - back of space is house wall. Can probe 1050mm on the diagonal across the void. Pythagoras gives 425mm wide, which take as about 0.5m .

(R. Smith, 23Sep2023, 24Sep2023 (size))