Knocking soil stack

[LewisH80]

A few years back my bathroom was replaced as part of an insurance job. The layout was pretty much like for like,but with a slightly higher spec.
During the winter months, every now and then, I'd hear the odd knock from the boxed in soil stack. This year it's significantly worse. The upstairs neighbours are new and in and out their bathroom like there's no tomorrow (pull cord light switches are bloody loud)!

I've attached pics before the boxing in was done. Unfortunately I don't have anything before the plasterboard went up!

Also, here's a link to the knocking.

So I guess my question is, does this sound like heat expansion? I can usually hear water running when I hear the knocking.

 

[Madrab]

Yes - absolutely, that's what it is. Unfortunately you have an unusually loud knocking sound as it normally manifests itself as a clicking or ticking noise. Basically it's the soil stack moving, usually against the wood of a box section, as it expands and/or if galvy banding has been used to support the stack without anything in between it and the stack.

The only solution really is to identify where the stack is noisy, open that section up and sort out what the stack is pressing against.

On another note, is that toilet stub connected into the stack lower down?

 

[LewisH80]

Thanks, I'll be expanding the hole where the concealed shower controls are and taking a closer look.

Re the stub: I'm not sure tbh. I always thought it was separate. A few months back the toilet experienced some slow empty issues (nothing a few buckets of water sloshed down wouldn't fix), but the bath/sink were fine, so I guess they join outside the building.

 

[Madrab]

Re the stub: I'm not sure tbh. I always thought it was separate. A few months back the toilet experienced some slow empty issues (nothing a few buckets of water sloshed down wouldn't fix), but the bath/sink were fine, so I guess they join outside the building.

reason why I say that is, if it is a separate stack then it should be vented by at least an AAV, can't quite see what's on top of it.

 

[LewisH80]

I think it's just a cap, but it's been so long since I saw it, I can't remember. Never had any issues with the toilet. So maybe it is.

 

[Madrab]

Never had any issues with the toilet

A few months back the toilet experienced some slow empty issues

 

[LewisH80]

D'oh! Yes! Good point. But that's been like once in the 7yrs I've lived here.

Anyway. Got my little endoscope out, I can see the big chunk of 2x4 that's butted up against the soil pipe. Its also holding the controls for the shower and further up the arm for the shower head... Time for the tiles to come off!