On Wednesday, 26 June 2019 18:17:47 UTC+1, DerbyBorn wrote:
I need to bore a hole in a joist to take a shower waste. Reading the regs
tells me that in a 20cm Joist the max hole can be 32mm

I need to pass a pipe of 42mm diameter!

The joist is right next to a wall at the outer edge of the house - load on
it will never be high.

Pragmatically - would you go ahead and bore the hole?

The regs on joist sizes have nothing to do with safety. They're more about meeting noise transmission targets. If OTOH it's an old house with bouncy floors I'd add noggings each side of a large hole. But 2" out of 8" isn't large.


NT