Robin Banks

Thanks for all the useful posts. In case anyone has a similar issue in the future, I contacted Building Control and asked they to clarify the position with respect to the building regs. They said that if there was a SVP on the architect's drawings, they would have expected that to be fitted. Failing that they would have expected there to be at least an air admittance valve in the boxing to the back of each toilet, as given the drainage layout that would be a requirement. If there was no space for standard size air admittance valves, smaller ones (50mm) could be used.

Nope - both the WC and ensuite are like my bad drawing - i.e. sink waste goes into pan connector behind WC and then that disappears into the ground.

That's a good explanation, thanks. But there are no AAVs or SVP in the extension, that's the thing I have a problem with. PeterW explained that the old stack in the house (which has an SVP) is enough, but I just don't understand why since it can't prevent sewer gas from (potentially) getting into the extension. At least, I don't think it can.

I guess the thing I'm having difficulty getting my head around (as a newbie to all this) is how the vented stack in the house can prevent sewer gas potentially entering the extension when a toilet in the extension is flushed ? It can't can it ? Would it not have been better for the builder to follow the architect's plans and put a SVP in the extension, or - failing that - have AAVs on the toilets ? I mean, better to have them and not need them than need them and not have them, right ?

Yes, the toilet in the old part of the house is attached to a classic cast iron open vented stack. But that whole thing isn't tied into the extension at all, it lives by itself on the other side of the house.

Couldn't get any photos because it's so cramped. But, I have drawn a picture of what's there. No sign of anything resembling an AAV

Thanks for the replies. Have had a good look around and there's definitely no SVP. I'll open the boxing-in of the cisterns and get some pics.

I can see where the toilet soil pipes disappear into the poured concrete floor and there's no sign of anything that looks like an AAV. Am I right in thinking that any AAV would need to be at least at the height of the sink overflow ?

Building Control has signed the work off.

I don't mean to hijack the thread either, but I think this post fits into the general flow. We've just moved into the house after having a single storey extension built. I've noticed that there's no soil vent pipe (SVP) anywhere (contrary to the architect's drawings), and nor do there appear to be air intake valves (AIV) fitted internally any place that I can see. I've checked inside the cistern boxing, and there's no sign. Since they need to be accessible for maintenance I can't imagine they would be any place else. The soil pipes for the ensuite and WC aren't tied into the existing stack either since that's upstairs on the other side of the house. I've had a look at Part H of the regs, but it's a bit confusing to the layman - can anyone advise me if one or other of these systems (SVP / AIV) should have been installed to comply with building regs ? Thanks in advance. Rob (long time lurker, first time poster...)