I'm unclear whether or not I need an Air Admittance Valve in a new WC and wash basin installation in my home. It will be easier for me to build an external venting stack in this instance. There's very litttle room for a AAV stack inside the new bathroom. The new bathroom is on first floor, within attic trusses. Here's the plan:
WC coupled to soil pipe which runs horizontally, within the floor void, for 2.5m to exit external wall at 2.4m above ground level. Soil pipe then connected to T piece: downwards to join existing foul waste pipe, upwards to a vent sitting 1.5m above the roof gutter.
Within the bathroom, at floor level, I want to join a 32mm washbasin waste to the WC soil pipe using a boss or collar fitting. The washbasin is 2ft from the WC.
My Questions are:
1) Do I need an AAV on the soil pipe as well as the external vent? (If I don't, would a plug of water from the WC flush not be able to siphon my washbasin trap before the plug reaches my external vented pipe, 2.5m away?)
2) If I do need an AAV, can the AAV stack be offset from the soil pipe exit or must it sit vertically above the soil exit (with the WC pan then having to be offset)
3) If I do need to fit an AAV, can I do away with the external vent stack?
I'm sorry if these questions seem to have obvious answers but I'm no clearer, after reading Part H regs. and various other threads. I'm restricted in where I position pipes etc by the massive 8" x 3" floor joists in this old house and the narrowness of the wall where the lav and basin need to fit.
WC coupled to soil pipe which runs horizontally, within the floor void, for 2.5m to exit external wall at 2.4m above ground level. Soil pipe then connected to T piece: downwards to join existing foul waste pipe, upwards to a vent sitting 1.5m above the roof gutter.
Within the bathroom, at floor level, I want to join a 32mm washbasin waste to the WC soil pipe using a boss or collar fitting. The washbasin is 2ft from the WC.
My Questions are:
1) Do I need an AAV on the soil pipe as well as the external vent? (If I don't, would a plug of water from the WC flush not be able to siphon my washbasin trap before the plug reaches my external vented pipe, 2.5m away?)
2) If I do need an AAV, can the AAV stack be offset from the soil pipe exit or must it sit vertically above the soil exit (with the WC pan then having to be offset)
3) If I do need to fit an AAV, can I do away with the external vent stack?
I'm sorry if these questions seem to have obvious answers but I'm no clearer, after reading Part H regs. and various other threads. I'm restricted in where I position pipes etc by the massive 8" x 3" floor joists in this old house and the narrowness of the wall where the lav and basin need to fit.
