I believe what you were asking about was drilling a hole through the 9 1/2 inch dimension not the 1 1/2 inch dimension. And if so the 1 1/4 rule applies here in Kansas. Most pre-fabed joist use to have knock-outs for plumbing and wiring. ( I don't know if they still do or not) Here most joist are Pre-Fabed 2x4 floor joists. I think this is what you asked, if not I new to the forum but have been reading for sometime and I know someone out there has the answer.
