Loft conversion en-suite waste length help

[Vale46]

Evening All

Have had some very useful help so far in reading this site so now time to ask my first question.

Please be gentle

We are in the process of a loft conversion that has an en-suite incorporated we had some basic plans done by an architect to inculude this but as we come to plumbing time we are struggling with the maximum waste pipe length arrangement.

I understand waste pipe at 40mm is a max run of 3m I need to run about 7.5 to get to soil drop.

Is it possible to run sink and shower waste at 40mm at 7.5m if I include an AAV? Fall is not an issue as new floor is way above our exit void into small back loft which is not part of conversion.

Running a new soil pipe for loo but on other side of wall, fall tricky to get 40mm into due to brick obstacles

Thanks in advance

 

[Riley]

Can you upsize

 

[Vale46]

Hi yes I could go to 50mm or run even more 110mm after a 3m stint of 40mm under the floor thanks

 

[Riley]

Then id do that

 

[Vale46]

Ok the 110?

 

[Aire]

I'd run it in 2" but where are you getting your max run measurements from? I wasn't aware there was a max run for shower wastes.

 

[Vale46]

Building control visit yesterday and the dreaded google !

 

[Vale46]

Saying that I’m still not 100% bco was too sure either

 

[Riley]

I'd run it in 2" but where are you getting your max run measurements from? I wasn't aware there was a max run for shower wastes.

Why did you think there was no max??

 

[Aire]

Why did you think there was no max??

Because it's something I've never come accross before. Even now when reading part H of the building regs I can't find anything specific to shower and bath wastes, the only appliances it mentions are toilets, bidets, basins and urinals, and from what I can tell that's on unventilated systems. Mcalpine state there is no max length for baths or showers but I guess that's not an official document. I've always gone off the basis of keeping my runs as short as possible which adequate fall but I'll admit I have ran shower wastes longer than 3m when necessary.

 

[Riley]

I was always taught at college to not exceed the lengths mentioned

 

[Ric2013]

Ah. Well there is something about sprinkler taps on basins that don't have plugs so I see the logic.

If the shower has no plug, then the trailing discharge will prevent the trap from being left dry, even if siphonage occurs. But if there is a sink (do you mean basin?) also, then this is not relevant to this situation as the basin would indeed suffer from a siphonage situation.

Not convinced AAVs or waterless or resealing traps are acceptable in a new-build situation and I think the 'correct' way is secondary venting, but perhaps it's just a case of having to wait for the Approved Documents to catch up with modern practices.