Whiffy Bathroom

From time to time there\\\'s foul smells in my bathroom. Seems to eminate mainly from the bath waste.

Previous occupants of the house built an extension and after adding an en-suite adjoining the existing bathroom, the \\\"Plumber\\\" seems to have designed a drainage system with no ventilation to the stack (lot of gurgling using various appliances). His/Her grand design, is contained within a 12in cavity between the stud wall of the new en-suite and the old exterior wall of the existing bathroom.

The stack serves 3 Toilets(downstairs WC), 3 wash-hand basins, 2 Showers(1 Pumped), kitchen and utility room sinks.

Considering the downstairs seems to function OK, what\\\'s my cost effective way to ventilate the stack??

Did building control approve these alterations?

Thanks for the prompt reply Ricarbo.

Problem is, the guy I bought the house off was the architect who designed the extension. These people seem to know how to hide the obvious. The Control Officer seems to have been more concerned with tiny vents in double glazing rather than the important issues.

Didn't honestly think I would have any come back from them anyway?

The cavity is two stories high and half the length of the house. I can't reach as far as the main stack junction coz it's behind a tiled portion of wall, but the branch for the new WC runs at low level just behind the plasterboard.

What about containing an Air Admitance Valve in the cavity and bossing into the top of the branch?

Hello,
I had this problem and found that replacing the U-bend under the bath with a deeper one fixed it. The original bend was very shallow and the water level in it fell when emptying the bathroom sink.
Regards, pcr.

If the smell is coming from the bath trap, as the previous poster stated the trap is probably having the water (seals from rising smells) sucked out of it allowing the stack smells to escape. You can either put a deeper trap on the bath or I would recommend replacing the exiting trap with an anti syphon trap.
With regards to the stack, I'm not sure where it is terminating. Presumably not outside above the roof, but inside somewhere. If it is the later then it definitely needs and air admittance valve if it hasn't already got one. The other point being that you should have your stack open vented somewhere i.e. your not supposed to have just one stack with an AAV. If it is a second stack in your house and the other stack is open vented, then its allowed.

Cheers for the quotes folks.

Problem sorted at the weekend. As suspected there was no vent because seal loss didn't occur at the bath alone. Thought it prudent to fix it right, so bit the bullet and fitted a vent via lead slate.

Guess what??? After using the shower in the bathroom the smell re-appeared from the bath. Replaced shallow trap with re-sealing one.