So I’m currently designing my new bathroom. I live in a 1970’s apartment block and am on the top floor. My neighbour underneath me has previously had problems with water leaking behind my shower and down the plumbing stack onto her ceiling. My builder has told me that I won’t need to waterproof the plumbing stack as water won’t get into there any more. He was also unsure he was allowed to waterproof inside the stack. Is this correct? Should water be able to get down the plumbing stack in the first place? And are there any issues with waterproofing my floor?

I’m currently designing my new bathroom. I live in a 1970’s apartment block and am on the top floor. My neighbor underneath me has previously had problems with water leaking behind my shower and down the plumbing stack onto her ceiling. 

My builder has told me that I won’t need to waterproof the plumbing stack as water won’t get into there any more. He was also unsure he was allowed to waterproof inside the stack. Is this correct? 

Should water be able to get down the plumbing stack in the first place? 

And are there any issues with waterproofing my floor?