Thanks that exactly proves my point. As your diagram says. You’re allowed to drill a hole at a max of 1/4 the width of the joist. So even if that’s an 8 inch wide joist the biggest hole you can put in it is 2 inches wide.

That looks like 4" waste pipe. So to drill a hole through a joist for that the joist would need to be 16" inches wide.

So you can’t just drill holes in joists in the “middle that isn’t critical” As I said there are specific rules about where the size of holes you can put in joists because the size and location matters very much to the strength of the joist.

deleted by creator

No, no they wouldn’t. In the UK there are very strict rules about notching or putting holes in wooden joists. Precisely because it weakens them.

Full joist the load is spread through all the fibres of the timber. Drill a big hole in the middle and the load only goes through the top and the bottom fibres. So essentially it’s as strong as those two blocks of fibers. So why not make the joist just that thin the the first place then? The answer is because it’s nowhere near as strong.

There are various steel, composite and wooden joists with a special frame construction that can have hollow sections. A standard piece of timber with a big hole drilled in the middle of it is not one of them

I hope whomever owns the rights to that photo makes it available to southpark.

The photos they’ve been using for trump are perfect and this would fit right in!