Is this OK ?

[STEVEROG]

I need to add soil and waste connections for two new bathrooms. The sketch below shows what I intend to do. Does this look OK?

Note that all the pipework except the red ones, are on the outside wall of the side of my house. The red pipes are my attempt to show the pipe runs that are inside.

All the pipework will be ring seal PVC-U. The soil is all 110mm, all waste is 40mm except the run from the basin which at 4m long I thought would be best if in 50mm - I have also included an AAV for good measure on this run.

All the soil 110 pipes will have 18mm/m fall, could get more if this is better?

All the waste pipes will have 40mm/m fall, could get more or less if this is better.

I have included the short vertical pipe drops (shaded blue) mainly to ensure that the falls on the waste pipes are not too steep but also to ensure that there is separation between waste connections on the stack. That said, none of the connections are at opposite sides of the stack, they are all either on the same side or at 90 degrees from each other so perhaps I don't need any height separation.

I think I may need some access bends on my short vertical pipe drops ?

The distances from the backs of the toilets to the soil pipe connection outside are all pretty short. Toilets 2 and 3 are less than 20cm, toilet 3 is a bit longer at around 1m.

I'm not sure if the conventional open vent just above the roof is the best way to go for venting, was thinking perhaps running with an external rated AAV instead?

Not sure about the exact type of AAV for the basin, any recommendations welcome?

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[Hufty]

As long as it works its okay (to paraphrase the Secretary of State in Building Regs H). Once you've seen the plumbing in a mill conversion you'll stop agonising about gradients etc and just get it in with the bubble on the line of your spirit level . A lot of the pipe lengths etc in the regs are to ensure you don't need the extra ventilation pipework of the past and/or air admittance valves, anti vac traps etc.

What you don't want is a massive fall otherwise the water swishes away leaving the sediment behind. Most plastic fittings assume a 2.5deg fall that usually works, and for soil pipe "anything off level" is okay, surprisingly. NVQ3ers will probably be able to tell you the self-cleaning angle of a pipe.

50mm diameter pipe for a basin is excessive - would stick with 32mm (maybe into 40mm) myself. There's a graph of gradient v pipe length somewhere in the regs would have a look at that.

If you're worried about the basin run, fit a HepVO trap they solve all sorts of air admittance, trap seal loss, gurgling issues.

Make sure there's a gradient on smaller pipes going through the wall - don't want it all freezing in a cold snap.

I prefer solvent weld waste to pushfit for waste pipework.

Open vented stack is preferable to a Air Admittance Valve outside btw.

All IMHO.

 

[STEVEROG]

Thanks for input, was wondering if I was going to get a reply!

I will crack on with the 18mm/m run on pretty much everything but following your point about the massive fall I will definately need to keep those little 'droppers' at the end of the runs to keep the falls sensible.

I only went for a 50mm pipe on the basin based on the fact that the regs doc called for that size with a very long pipe run (mine is about 4m total). Of course, the numbers are for unventilated runs, as I am going to put in an AAV at the basin end of the long run then perhaps a 40mm pipe is probably good enough.

I assume the HepVo trap solution replaces a standard wet trap and AAV?
If that's the case then I may go down that road.