Soil vent pipe causing mould on riser- with pics

[joefuller]

Hi all,

I searched for existing threads and while there are other SVP condensation issues, none have quite this problem.

In our bathroom, there is a riser built into the wall which has had mould developing for several months- wipe it off and it soon comes back. It is also now 'blowing' the plasterboard out. Inside the riser is a SVP which terminates in the loft and has condensation all around the top of it. The loft is insulated but fully ventilated at the eaves etc. There is no water or anything at the bottom of the SVP itself and I have checked under the FW manhole and there's nothing untoward. All taps, plugs etc drain normally. What I think may be happening is that the warm air inside the SVP from all the hot water etc in the drains is meeting the cold outdoor air in the loft causing condensation on the exposed top few inches and then running down inside the riser, causing mould to come through. House is mid 1980s, single story if that is relevant.

Does anyone concur with my theory, or have an alternative and does anyone have any idea how to stop this?

Thanks all,

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[Gasguru]

The SVP needs terminating through a roof vent...new build bodge by the look of it.
I'm surprised the roof timbers aren't rotting..don't underestimate the huge steam cloud from a bath emptying.
And that pipework needs insulating or at least roll the loft insulation over the top of it.

 

[joefuller]

That is a very good point Gasguru, thanks. I'll go up there when the kids bath is emptied and see what happens. And yes, the bare pipes has just occured to me. Might be tricky to run that through the roof though as this is a listed building (yes, I know 1980s! It was a listed barn before conversion in the 80s and still is even though only 2 walls of the original structure remain...). This whole roof area was replaced by previous owners only about 5 years ago after a fire, which is why it all looks new.

 

[Madrab]

Not unusual these days to see that as they don't want to spoil the roofline. Normally though there should be a vent slate that that would connect to or that pipe would have a durgo (AAV) on it to stop condensation/smells filling the attic space. There may have been one but it's caused an issue with the soil pipe draining properly and someone's removed it. It also looks like someone has tried to cover it with plastic at some point?

In the sort term I stick a durgo on it but if you have an issue with wastes/toilet not draining properly then look to get a roof vent fitted.

 

[RonnieE]

I have literally never seen that before but it is almost certainly the culprit causing the mould.

Useful article here on condensation in loft spaces - Condensation In Loft - Best Fix | WaterLeak.co.uk