Can a 110mm strap boss be attached to top surface of horizontal waste pipe ?

Question

The location I am considering placing a the bath in my new bathroom layout is with the bath waste almost directly above a horizontal run of the 110mm bathroom waste pipe running under the floor. This section of 110mm pipe connects the soil stack to a 110mm air admittance valve, thus actually currently has no water running in it.

Due to space constraints it is not possible to get a strap on boss on the side of the 110mm pipe and connect the bath waste to it (structural I-beam joists are in the way) so is it permissible to connect the boss to the upper surface of the 110mm pipe an pipe the bath waste to that ?

Might be slightly noisier ?

Is there a pipe wear issue due to the 110mm "drop" ?

Heliotrope Smith · Accepted Answer

It is perfectly acceptable to connect to the top of the soil pipe.

Roger Mills · Answer

I see no problem with that as long as your 'horizontal' pipe has a slight *fall* towards the stack, and not the other way!

The Medway Handyman · Answer

I've seen many basin wastes connected into the top of a horizontal soil pipe, so I wouldn't think you would have a problem.

Lobster · Answer

Yes - I trust the AAV is not mounted on the end of the (near?) horizontal pipe, but rather, is mounted so it points skyward?David

Ian_m · Answer

The AAV is mounted on a vertical section at approx 1m above the floor level.

Yes the pipe does slope towards the soil pipe rather than the AAV end.

Only other thing, my brother who is/was a plumber/site manager came up with is don't make the bath waste connection too short as he has met leaking bath wastes where it dropped almost straight into a 110mm pipe and had no give or movement. After about 2 years it started leaking at both boss connection and bath plug as there was probably no "give" in the waste pipework to allow for settlement/movement of both the bath and waste pipe. He fixed by running the

40mm bath waste pipe about a foot along the 110mm waste into a new boss thus allowing some flexibility between the bath and 110mm waste.

Can a 110mm strap boss be attached to top surface of horizontal waste pipe ?

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