Possible leak from soil pipe outside causing damp

15 Feb 2024
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United Kingdom

I’m looking for some advice.. we’ve recently moved into a new property and have noticed that the soil pipe external to the house is leaking every time the toilet is flushed. It’s partially covered by decking but we can see clearly above the part above decking and have tested it so we know it’s definitely leaking. Almost exactly where the pipe is on the inside of the kitchen is a very bad damp patch on the wall and on the floor. To complicate things, there is failed seal around the door and possible condensation damp behind the washing machine. I don’t think these are all related but they could be.

first and foremost I think we need to fix the soil pipe as I’m sure this is what’s causing the damp on the floor and up through the wall. (I’ve attached pictures). The black tape behind the pipe was covering a patch of wall that hadn’t been fully rendered and was crumbly cement which I think was also letting water in.

Has anyone suffered a similar problem? And does anyone think the damp behind the washing machine could be a result of the ground becoming particularly sodden from the leaking pipe?

Our next steps are pulling up the panel of decking by the soil pipe to have a proper look and then calling a plumber to fix the leak.

Thank you in advance for any advice!


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Yeah we thought that could be an issue having looked at some other threads!
Can we have some pictures of the whole setup there please. If the Flexi pipe is going to a WC, that may well be part of the issue, the washing machine drain hose looks to have been extended with more hose, (not ideal), and need to see the setup with the soil pipe externally to advise best on how to go about sorting that out.
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Check the gradient of the decking, it should have at least a 1 in 80 slope away from the house. Pour some water on it a metre away from the house, if it runs towards the wall you have your culprit and it needs pulling up, re-laying if you want but with a slope.

Also there should be a gap between it and the wall
Looks like significant penetrating damp, which has come through after the refutb ( plaster floors and skirting look new(ish). Fixing the soil pipe should be relatively straight forward.
Thank you all for your replies! Our next fixes are going to be repairing the leaking pipes. We had a drains survey and they’re cracked below ground too. And then remove the decking completely as we’re not wedded to it and see if that improves the situation. We also have the same damp mirrored in the corner wall in the exact spot upstairs so it could be just condensation or potentially a leak from the roof/cracked tender outside.
It would need to be a large (prohibitive) gap, in order to prevent the splash effect, especially if the decking is set close or at DPC level.
I'm wondering if it's basically tipping water into the wall, i.e. the contents of the decking are being held against and injected into the wall.

Even if it did slope away from the wall, some would still find its way to the ends of the planks. It's vastly preferable if this drips into the soil below.

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