Bad sewer smell.

[Andy Sithers]

Advice please! This is driving us bonkers.

Our house has a lean-to extension, which houses the downstairs toilet.

Main waste pipe from the bathroom passes down into the lean-to, and then out to the sewers. Downstairs toilet is connected into that. I'm going to assume that the pipe vents into the lean-to roof void, but since there's no access, I'm only guessing.

Problem is the awful sewer smell that we get in the room from time-to-time. No signs of leaking, and smelling the exterior vent into the void (yes, I stood on a ladder and sniffed) seems OK.

I've recently rodded the drains, some way away from the toilet (quite badly blocked). I'm wondering if things have backed up, but can't figure out how (1) toilets would flush OK, and (2), how the smell would come out.

Next step is probably to lift a couple of slates to check how the pipe is finished - hoping there's a one-way valve on there.

Any thoughts, before I post about breaking roof slates?

Cheers

Andy

[Paul Mc Cann]

Check the seals at all the junctions down wind from the pan. They might not necessarily leak water but could leak odours.

[Peter Stockdale]

time-to-time.

Seems a funny system that vents in to a roof void - no wonder you get the odd pong or two. Twould be better for the system to vent to open air from the highest point in the system normally just above the eaves. Regards Pete

[Andy Dingley]

Not unusual these days (and less susceptible to rain ingress through a roof flashing). There should be a non-return valve to keep the smell in. However these have been known to fall off, hence the pong.

[dg]

Is there still some water seal in the wc pan or basin after flushing the upstairs wc?

In some cases waste flowing down the stack can suck the water seal from the ground floor pan or basin and let a waft of sewer smell through. If this is the case an additional stub-stack and airadmittance valve is required.

dg

[Peter Stockdale]

Whilst I accept your point that it may be unusual these days, your point that about rain ingress through flashing is invalid as most traditionally built properties have the vent stack external to the roof.

Pete

[Andy Dingley]

There are three ways to do it - the old way (the whole pipe is external), the new internal way with the valve, and the typical method of recent decades - having soilpipes internal to the walls, for visual reasons of less cluttered exterior walls. Those are the ones where it's an extra roof flashing.