Converting WC Direct to Drain into Soil Stack for ensuite - Waste logic check... (images included)

[richardsimkiss]

Hi all, DIY home renovator here - learning plenty as I go... Current project has seen me reading through the Part H regs which has taught me a huge amount, but of course being a renovation project with lots of little quirks, I could greatly benefit from the wealth of knowledge on these forums to give some advice/feedback on my plans, and whether there are likely to be any problems with it (as well as any recommendations).

Current Situation:
The property is a bungalow, so all ground floor stuff with suspended timber floors. We currently have a Toilet connected directly to drain, no stack or vent. The shower and basin currently drain to a gully outside.

Current

• richardsimkiss
• 7 Aug 2018

Proposal:
The plan (/hope) is to rearrange the bathroom layout, moving the toilet position, and also adding another toilet as a 'cloakroom WC' for guests. I cannot (or rather would rather not) add a vertical soil stack where the current drain is sited as there is a window there which would have to be blocked up, it would also reduce the space available for the shower by the amount required to box in the stack.

After realising that it probably isn't a good idea to drain everything to the drain without some form of venting, I've finally ended up with the proposal below, which has a vented stack, but then a horizontal run before a final drop (marginally over 450mm) to the main drain.

Proposed

• richardsimkiss
• 7 Aug 2018

(This is a schematic of the waste pipes rather than actual layout/position of each WC/basin etc).

Is the horizontal run of the 'stack' acceptable? Anything else I should be wary of? (the under floor branch where the two 110mm pipes join won't actually be opposite each other, so there won't be a crossflow problem).

Huge thanks in advance,
Rich.

 

[KenGMac]

richardsimkiss, good evening

Can I suggest you google 2 things?

A/. Durgo air admittance valves [will cut down on the vertical stack]

and

B/. Anti-Siphon Basin traps

Ken

 

[richardsimkiss]

Thanks Ken, I'd already looked at AAV's, which I'd use and terminate up in the loft space (for neatness and consistency, I'd box the stack into a widened partition wall) - I just wasn't sure if an AAV was sufficient, or if it needed to be a full vent. We're the last / highest property on the drainage run (if that makes any difference) so no ventilation in the drains further up from us. Having spoken with our only neighbour (down drain of us - also a bungalow), they have fitted a durgo in their loftspace.

Good shout on the Anti-Siphon Basin traps - with these and the above in mind - any idea if the setup is 'appropriate' in relation to regs?

 

[Hugh Jaleak]

Highest point of the drain needs to be vented. AAV's have their uses, but in your situation I'd want to vent it. Will prevent any possible issues with positive pressure, which could occur if both WC's are flushed at the same time, (unlikely but not impossible), and then the risk of blowing a trap somewhere else.

I know that's only a schematic, but if nearer, connect the WC's directly to the drain on a separate branch rather than commoning the 2 together under the floor.

 

[KenGMac]

Is it possible to excavate externally and connect a vent pipe to the main drain outside the house?

That way, being the highest point you can carry on internally without too many issues?

 

[richardsimkiss]

Thanks for your input guys - really appreciated.

Ken... the drain currently runs out the property underneath a window (see plan below), so unless there was more excavation work do to move the drains, I'd end up with a soil stack outside the window (or I could always block up the window I guess)... I'm also trying to keep the job as 'neat' as possible, so trying to avoid a vent pipe Swan necking above the roof line as it's right next to the dining room. Of course I appreciate these things are functional, but if I can find an aesthetically improved solution in any way then I'd rather go down that route.

Hugh, thanks for the thoughts - it ties up with my (non professional) gut feel that venting would be a better option... My lack of knowledge/experience means I'm struggling to get my head round what you mean by connecting both WC's directly to drain... I've mocked up a plan view to give a better idea of where things are laid out in relation to each other... I've also changed slightly how I'm thinking the basins would drain - (thinking if I could link 3 basins and run them into the stack, that would be great from a neatness perspective... (either using anti siphon traps, or a durgo/AAV in the loft for that 40mm pipe run)

Drain point in top-left is the existing drain... any further thoughts hugely appreciated

 

[Hot&Cold]

any further thoughts hugely appreciated

How about considering employing a plumber to do the new soil pipe and dealing with building control

 

[richardsimkiss]

A good suggestion Old&Cold... though while forums like this exist to share knowledge/experience, I find it far more rewarding experience to learn the skills and do it myself. (It also sits a lot more favourably with the renovation budget).

Of course if I can't find an answer with the forums help, I'll end up paying for a plumber

 

[Hot&Cold]

Of course if I can't find an answer with the forums help, I'll end up paying for a plumber

The new soil pipe is considered notifiable work,often cheaper,quicker and neater to have it done by a plumber who will either self certify their work or use an inspector.

sure, there is plenty of other work to keep you busy

 

[richardsimkiss]

All valid points O&C (and yes... a good 12months+ work ahead of me!).

I could apply similar logic to a lot of the renovation work (certainly quicker, probably neater, possibly cheaper [depending on any mistakes]), alas the budget is such that I have to be rather picky about when I fork out for an experienced professional... I'll continue scrounging around for info from the kind folk of forums like this until I deem myself properly 'stuck'.

 

[KenGMac]

richardsimkiss, good evening again.

OK another idea?

How about you consider fitting not one but two AAVs /Durgo valves??

Site them behind each toilet? by boxing out a section to the rear of the WC it will be possible to install a valve at the top of the two runs? directly above the connection to the individual WCs?

I have seen these valves set to about 1.0 m. above floor level, the boxing in can terminate above the valve or be taken up to ceiling height and as discussed above up and into the loft space [saves a load of phaff with roof tiles or slates?]

Ken

 

[Hugh Jaleak]

The plan view makes more sense than the elevation, I can see the layout now. Is there space to bring a vent pipe up alongside one of the WC's? Can reduce to 82mm pipe if need be for the dry section. (Then fit a AAV on the other WC for belt and braces.)

Wastes, common into 40mm pipe, provided you dont exceed 3m in length. Fit an anti vac trap on each basin. Basically, these are the regs you need to follow. https://assets.publishing.service.g...achment_data/file/442889/BR_PDF_AD_H_2015.pdf

 

[John D v2.0]

Id suggest taking the shower into the stack on its own to reduce the chance of communication between the shower and sinks. Or increase to 50mm pipe when they combine.