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I am fitting a shower tray upstairs. I want to run 42mm shower waste pipe for a run of 1. 6m. The problem I have is that I would have to drill a hole 45mm in a 120mm joist. These joists I don't think are structural as they run from rsj to rsj. I would have to go through 3 joists. Is this acceptable or should I drop pipe into kitchen underneath and run in pipe box.