Drainage for understairs WC

[sjh88]

Hi guys,

I’m looking to put in a WC cloakroom under the stairs in my house by moving the stud wall. I had a few questions in relation to the drainage. It is a suspended timber floor, although there isn’t loads of space under the joists. Having dug up the drain near the stack, I think I should be able to run the proposed branch to the existing stack @1.80ish.

In terms of the regs, I understand a new WC branch has to be under 6m from the stack, which this just about is. For rodding access, I wondered if I could incorporate a rodding eye into a stub stack behind the WC (would this need an AAV?). The other alternative I thought might be to incorporate a mini inspection chamber where I have shown the Y-connection to the existing pipework?

Finally, having dug up underneath the stack, I was surprised how shallow the pipe was - instead of a proper rest bend they have used a short radius standard elbow…does anyone know if you can get black rest bends that can be used above ground or should I just leave it as is?

Cheers!

 

[jj4091]

Where is the nearest inspection chamber

 

[sjh88]

Where is the nearest inspection chamber

I believe it's next door to the right as you look back at the house - his garden is extremely overgrown so it's hard to say for sure - definitely not one in my garden

 

[Hugh Jaleak]

Couple of 45° above ground bends would be better rather than the current short radius bend at the bottom of the stack.

What I would do. Expose some more of the Salt Glazed Collar just visible in the end of your trench, and cut that off. Using a suitable coupling, run from there in plastic, drop in a 45° Junction and reconnect existing stack to the branch. Fit a rodding access in the stack as close to ground level as you can.

From the junction continue forward slightly, then fit a mini chamber, and run from there to the proposed WC position. Cannot stress enough, if you're working on a 1:80 fall, it must remain constant across the length of the run.

You wont need rodding access internally, (you really do not want to be trying to unblock a drain run from inside the property, unless you plan on replacing the flooring and redecorating afterwards!), but an AAV on a stub stack adjacent to the WC is not a bad idea.

 

[sjh88]

Couple of 45° above ground bends would be better rather than the current short radius bend at the bottom of the stack.

What I would do. Expose some more of the Salt Glazed Collar just visible in the end of your trench, and cut that off. Using a suitable coupling, run from there in plastic, drop in a 45° Junction and reconnect existing stack to the branch. Fit a rodding access in the stack as close to ground level as you can.

From the junction continue forward slightly, then fit a mini chamber, and run from there to the proposed WC position. Cannot stress enough, if you're working on a 1:80 fall, it must remain constant across the length of the run.

You wont need rodding access internally, (you really do not want to be trying to unblock a drain run from inside the property, unless you plan on replacing the flooring and redecorating afterwards!), but an AAV on a stub stack adjacent to the WC is not a bad idea.

Much appreciated Hugh, and that solution makes sense - forgive the terrible drawing, but is the attached sketch along the right lines? I assume I could use something like this for the 45 deg juntction? https://www.roof2floordrains.co.uk/...-junction-ds678428.html#/1065-pipe_size-110mm

What would be the preferred fall for a WC waste pipe, 1.40? I thought given how smooth pvc was compared to old clay, anything up to about 1.110 was pretty good?

 

[Hugh Jaleak]

Sketch is spot on, only alteration I'd suggest is, to use a slow radius bend either side of the chamber and use the through channel for the flow, avoids waste fouling and building up on the opposite benching.

That junction is fine, they're all interchangeable between the manufacturers, see who's cheapest!

1:40 is rule of thumb for 4" drain, but as low as 1:100 can be got away with, provided the fall is constant along the length of the run. (You don't want any dips or 'bellies' where waste can collect.)