Sewer smell after rain in basement bathroom

[ds99bwood9]

Hello all,

We live in a duplex flat (ground floor + basement) which always has a sewage smell after it rains. We have a standard setup (bath tub; sink; toilet) and it is used daily by the family, meaning the p-traps are full.

Last year a plumber fitted a Viva Magna self sealing waste valve was fitted under the bath tub which has minimal difference. Having scoured various websites/forums and eliminated all the obvious potential issues (empty p-trap; vent pipe; biofilm on the inside of the pipes) I'm running out of ideas as to what the issue could be (we've had 2 plumbers look at this already). We've also had someone look into the drains with a camera and they didn't detect any issues with the pipework leading to the property.

I'm more than happy to get a plumber back into the property to resolve this issue (quite frankly, it's posing a health and safety issue to my young family) and would happily take recommendations/offers from here (we're based in Archway, North London).

Any ideas appreciated.

 

[Chuck]

How is the toilet pan connected to the drain? If it's a flexible / convoluted ('bellows') coupling they are notoriously prone to developing splits.

Much rarer (I've only come across it once) is a faulty toilet pan casting with a hole that connects the rim to the sewer side of the trap. Try covering the toilet with cling film to test. Make sure your family knows about this test, and put the seat down with a brick or something on it to remind them. Otherwise you'll be woken in the middle of the night by your irrate wife trying to strangle you.

A sketch of your drains showing the relative levels, etc. might give us some ideas.

 

[ds99bwood9]

How is the toilet pan connected to the drain? If it's a flexible / convoluted ('bellows') coupling they are notoriously prone to developing splits.

Much rarer (I've only come across it once) is a faulty toilet pan casting with a hole that connects the rim to the sewer side of the trap. Try covering the toilet with cling film to test. Make sure your family knows about this test, and put the seat down with a brick or something on it to remind them. Otherwise you'll be woken in the middle of the night by your irrate wife trying to strangle you.

A sketch of your drains showing the relative levels, etc. might give us some ideas.

R.E toilet pan connected to drain - no idea to be honest. I know the seal failed a few years ago and needed to be replaced.

I've attached some building control drawings along with a photo of the bathroom.

R.E cling film test - hard to test as the smell isn't there now, only seems to be a problem when there's rainfall (yesterday was fairly substantial).

 

[Chuck]

The basic questions are:

(a) How is the inspection cover hidden under the bath mat sealed?
(b) How is the drain / sewer it connects to vented?

Can you confirm you have a 'combined drains system', i.e. rainwater and wastewater share the same sewer? I'm reasonably sure that this must be the case but I don't want to assume something that turns out to be wrong.

 

[PETE 123]

Try cheking to see if the intercepter cap is in place on main drain b4 sewer.

 

[ds99bwood9]

The basic questions are:

(a) How is the inspection cover hidden under the bath mat sealed?
(b) How is the drain / sewer it connects to vented?

Can you confirm you have a 'combined drains system', i.e. rainwater and wastewater share the same sewer? I'm reasonably sure that this must be the case but I don't want to assume something that turns out to be wrong.

In answer to the questions

a) The basement is tanked so as far as I'm aware, it's sealed under that
b) Not sure - how would I determine this info?
c) Combined drains system - how would I determine this info?

Would a drains survey be the best way to go (in order to answer the above and also determine if the interceptor cap is in place)?

 

[Chuck]

Would a drains survey be the best way to go (in order to answer the above and also determine if the interceptor cap is in place)?

I think so. I don't think you're going to be able to DIY this one and, as you realise, the health and safety of your household is at stake. I suggest using a company that specialises in drains and does this stuff routinely. Expect them to use pressure and smoke tests to establish how sewer gas is getting into the bathroom, and also check that the interceptor and venting arrangements are in good order.

 

[ds99bwood9]

I think so. I don't think you're going to be able to DIY this one and, as you realise, the health and safety of your household is at stake. I suggest using a company that specialises in drains and does this stuff routinely. Expect them to use pressure and smoke tests to establish how sewer gas is getting into the bathroom, and also check that the interceptor and venting arrangements are in good order.

Makes sense - appreciate the guidance and definitely want to get this sorted sooner rather than later.