rest bend needed on stub stack?

[23vc]

Hi
I know you need a rest bend or 2x45 bends at the bottom of a soil stack, but for a stub stack only serving a ground floor wc can I get away with a standard 90 bend? could have sworn I've seen this ok'd in the past but could be wrong!
reason is to reduce the depth of the pipe and lay after the footings are concreted ie avoid taking it thorough them. it will join a main stack about 2m away below ground.
Cheers
John

 

[Ian H]

I always (for the last 12 years) use a 90degree bend as a rest bend.

Reason being that all of the clay ones I replace are a very tight bend anyway.

 

[John D v2.0]

I thought the problem with standard bends wasn't so much the radius itself but the force exerted on the lightweight pipe by the rapidly changing direction of 6kg of water dropping down from a great height. That's why they're gentle curves and they have the fins on the back to hold in place securely.
However I've never done drainage and in practice building regs are designed for the worst case situation.

 

[23vc]

Thanks guys sounds like I'll be ok with it but will check with bco

 

[Ian H]

I'm not sure the reason. I've never seen a broken plastic bend, the only faults you seem to get on plastic are pipes put in flat or with back fall, then also displaced sealing ring where the pipe hasn't been chamfered and lubed.

Another thing to mention is t hat I wouldn't use a T for your connection into the existing, even if your joining it square on use a Y with a 45 in it.

 

[wessex101]

So a single rest bend fitting wont fit?

I had to look it up and Building Regs Approved Doc. asks for minimum 200mm radius bend at base of a stack but not specifically for a stub stack. Its more to do with allowing the solids to easily go round the bend rather than hitting a sharp 90 degree bend and potential getting stuck or losing all the momentum.

 

[^woody^]

or 2x45 bends at the bottom of a soil stack

No. Every stack requires a rest bend. A stub stack is still a stack.

 

[^woody^]

I had to look it up and Building Regs Approved Doc. asks for minimum 200mm radius bend at base of a stack but not specifically for a stub stack

What does BS 752 say? Especially in relation to any vertcal drainage - ie is there a difference?