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We are refurbing a bathroom, and are trying to figure out the ins and outs of the Building Regs. The sink is on the opposite wall to the (external) stack, and restrictions on floor structure mean we're routing the waste pipe around the walls to reach it. This takes us parallel to the bath waste.

A couple of questions for those with more experience than me:

- are we okay to add a 45 junction and discharge the sink into the bath waste pipe (40mm)? ...or do we need to keep both pipes separate (and punch lots of holes in our external wall and then somehow get them at sufficiently separate heights to hook them all into the stack while observing the rules about 200mm separation of offset branches)?

- the run from the sink to final discharge into the stack exceeds 3m - do we need to add an AAV to ventilate the branch?

Lastly, there is a separate shower. At present, the shower waste pipe runs internally straight from the trap to the corner of the room (about 2m, following the joists), then takes a 90 degree turn to punch through a joist and the outside wall to reach the stack. Is this okay? Can't see why not, but am getting paranoid!

"- are we okay to add a 45 junction and discharge the sink into the bath waste pipe (40mm)? ...or do we need to keep both pipes separate (and punch lots of holes in our external wall and then somehow get them at sufficiently separate heights to hook them all into the stack while observing the rules about 200mm separation of offset branches)?"

No they should be separate or you'll get syphonage. Why into the stack? Is there not a hopper available?


"- the run from the sink to final discharge into the stack exceeds 3m - do we need to add an AAV to ventilate the branch?"

I'd put an anti-vac trap in.


"Lastly, there is a separate shower. At present, the shower waste pipe runs internally straight from the trap to the corner of the room (about 2m, following the joists), then takes a 90 degree turn to punch through a joist and the outside wall to reach the stack. Is this okay? Can't see why not, but am getting paranoid!"

Its too big a diameter pipe to go through a joist and pipes should go through joists anyway - the joist should be notched. In any event its still too big to notch for if you do you'll seriously weaken the joist prolly leading to early failure. You should find another route.

Cheers

[quote] Is there not a hopper available?[/quote]

There isn't - and Building Control have indicated they disapprove of hoppers used in this way (existing is fine, but adding new ones is frowned upon apparently).

From rereading the Regs, we should be able to join the branches, but I guess this assumes it is being done outside at some distance from the appliances / traps.

[quote] You should find another route. [/quote]

I'd love to, but the joist has been put in running right along the outside wall (about half inch separation, if that) - so we have to go over, under or through it. Can't get over it from the shower outlet; under it and we'll fall through the ceiling of the floor below.

The correct choice is to run parallel with the joist as far as an exterior wall, take the waste out through that wall and deal with it from there.

Cheers