Venting sink/bath drain

[GCarnegi]

I need to run a 50mm length of 1st floor bathroom waste pipe across my extension ground floor ceiling (6m) then down the wall, before going through the wall and into the main drain.
There is no vertical 110mm waste pipe (soil stack) in the vicinity to tie into.

The attached picture shows the sort of thing I'm talking about.

Untitled

• GCarnegi
• 8 Nov 2011
• 1

My question is "do I need to add a vent to this pipe, going up into the attic?" If so, should I use one of those air admittance valves?

Instead of this, can I simply exit it out through a soffit / fascia, with no valve (like an overflow pipe)?

Does the fact that I'm using a 50mm pipe coming from a 40mm bath & sink waste mean that no vent is necessary (as the draining water will perhaps not "fill" the pipe, thus preventing a vacuum / siphon effect)

many thanks
Guy

 

[Bahco]

Use an anti vac trap on the basin.

I don't like the length of pipe though and it may get blockages in the future if you dont file the burrs off the edges of the cut pipe.