Single stack waste pipe

[P.J.]

Hi All,
Happy New Year.
I have a single stack waste pipe system in my house where the waste stack is inside the house, boxed in. This box is stopping me fitting the size of bath that I want and my question is, being that the waste pipe above the upstairs toilet connection only carries air, can I cut and remove the pipe from below the top of the bath to just inside the loft space and reconnect it with a smaller bore pipe ? This will allow me to fit the bath I want closer into the corner of the bathroom as I will be able to remove most of the waste pipe box and the waste pipe will still be vented to outside.
Thank a lot in advance,
P.J.

 

[ChrisR]

No. A 110mm soil pipe needs a 110mm air admittance valve.

 

[P.J.]

Thanks for the info. Can I not reduce the pipe diameter above the highest connected toilet and then increase it back in the loft space to the vent ?

Cheers,

P.J.

 

[Bahco]

If you do it you will be reducing the ventilation to your drainage and be against regs.
You could move your stack outside if you must have your bath where you want it.

 

[P.J.]

OK. Thanks guys. Don't really want to put the stack outside but am stuck with the bath position due to available floor space. Thinking cap back on !

Cheers,

P.J.

 

[shaggy]

Have the regs changed then? They used to say that the dry part of the stack above the top branch, so is just for ventilation, could be reduced to a minimum of 75mm dia.

 

[P.J.]

A difference of opinion ? anyone else have an idea on this one please ?

Thanks,

P.J.

 

[P.J.]

Can anyone confirm if I can reduce the dry section of a wate pipe please ?

Thanks in advance,

P.J.

 

[ChrisR]

I didn't know about the 75mm rule. It's most likely that anything important is in the Building Regs, which at least are easy to get hold of.

If you use a 4" aav then you should be letting air IN quick enough, and the holes are a darned sight smaller than say 50mm diameter pipe. This may be another case where regs will tell you what will work, and you have to use common sense, though you carry the can if there's a problem. But it's hard to think of a situation where a short length of 50mm could be an issue. The resistance of a bit of pipe depends on its length as well as diameter! Ultimately it's up to you.

 

[kevplumb]

FWIW sounds ok to me cant see a problem if the dry leg is 50mm

 

[htgeng]

FWIW sounds ok to me cant see a problem if the dry leg is 50mm

yeh. i suppose if it doesn't work, then the worst that can happen is the water is pulled out of the toilet bowl.. mmm nice!

 

[kevplumb]

then you put it back
the pipe not the water

 

[P.J.]

Thanks for the info Gents.

How about a rectangular section pipe with the same XSA (like the kind to vent an extractor in the ceiling space) ? That would vent as well as the round 4" pipe and I'd get my bath where I want it.

Or am I flogging a dead horse ?

 

[htgeng]

Or am I flogging a dead horse ?

yeh. the horse died a few days ago...

I think you should involve building control if you still want to change the vent pipe. They will give you the requirements and sign off your work.

The last thing you want to do is something that contravenes building regs. The reasoning that "you read it would be ok on an internet forum" would not be acceptable to them. Don't forget they can levy fines for illegal work.

 

[shaggy]

Perhaps things are different in Australia but I wouldn't bother bc with this one. I've looked at regs and it looks like a 75mm dia pipe for dry section is ok. If you used the 50x110 section duct then the csa would be greater than the 75mm dia pipe. You can get an adaptor to go to 100mm dia and could use a pan connector, either offset or flexi, to connect to 110mm stack. Sounds ok to me, so good idea PJ.