Fosse and Waste Pipe Venting Question

Is it normal here in France to not have a soil pipe vent? We have odours in our ground floor summer apartment, eminating from the drains. The fosse itself does have a vertical vent pipe, the top of which is abou 1m above ground. That is roughly at the same level as the shower drain in the apartment. I have checked all u bend and traps, they do contain water so the waste pipes are effectively sealed from “ambient” odours.
In my epxerience in the UK, the waste pipes woudl also be ventilated, either by an external stack or an intrnal one, venting at roof height. I do not have ay such vent, nor do any other properties when viewed externally. The French nor seesm to be to keep all waste plumbing hidden wthn the fabric of the building so vents may be there, just not visible.
The fosse passed inspection for the sale ( Acte De Vente Decmeber 2107) so it seems nothing is untoward, apart from the smell!
The house is built on a slight slope, our main accommadation is on the ground floor at the higher edge of the slope and the apartment underneath on the lower part. All of the waste pipes in the apartment are buried into the concrete floor, and exit the apartment at a point that is probably 1 metre below ground level. In a cave for the huse the waste pipes from the house come together in an inspection point and grease trap, before exiting. That exit waste pipe is joined by the waste pipes from the apartment, for which I cannot find any inspection hole or grease trap :frowning:

Anyway, my man uetsin is whether there should be a vent for the waste pipes at the accomadation end? If so, what are the conventions for such a vent?

Why not ask SPANC… presumably it is their documentation you have been given.

If they have “passed” a system, which appears to be failing… ask them directly… why this might be happening…

and do it sooner, rather than later… if there is a real problem it could be costly and you do not want to be forking out unnecessarily.

It could simply be that the vent pipe from the fosse needs to be taller… latest ones put in around here go up to roof height/ridge height…well away from windows etc.

Hi Martin, is the vent from the fosse clear? If not, and it is in effect creating a sealed tank, this could cause air (odours) from the fosse to be forced back through the water filled ubend traps when the fosse is filled with water flush (?)

Another thought Martin

If the top of the fosse vent pipe is on a par with the Appartment shower etc… it is obviously not high enough… (well it seems obvious to me, but I have been known to be wrong :relaxed::relaxed::relaxed:)

You could also ask SPANC about the lack of grease trap for the appartment. It may depend on how much usage the Appartment gets (or what they were told it would be getting)… just a thought… :zipper_mouth_face:

Hi Ray, yes, it does seem to be clear. @smw I too was wndering about the height. It is about level with the shower drain, if nit a bit lower. Does not help that halfway up the vent is 2cm hole where someone obviusly got carried away with a strimmer…

The ventilation pipe on our new fosse runs to the top of the roof of a double storey barn.


Are you near your Mairie? If so, have a chat with them, as best you can. Explain the smell etc. It may well be that they can have a talk with SPANC on your behalf… and then perhaps SPANC might do another site visit or at least explain what is going on and why… :zipper_mouth_face:

Thanks Stella, I am always wary fo asking a question of someone who may have a reponsibility for the subject :wink: At least until I am better prepared for the consequences of the answer…

Reading the latest instructions for installers (here at SPANC ) it seems there shoud be 2 ventilation pipes, miminum 100mm diameter. The first is in the waste pipes, it must be ventilated externally above all inhabitable rooms, this for air to enter the system. The second one is from the foss itself, and shoud be at least 40cm abve roof height, and more than 1m from the entry vent, this is the exit vent.
Itseems to me then that with the currnt vent being downhill from the house that my waste pipes are acting as the secondary ventilation. With the wind in the right direction there is possible enough of pressure differential for the gases to be pushed past the traps in the lowets points :frowning:
I would be happy to approach the SPANC now, I can even ask some more questions about some solutions I have in mind.
Since moving in in december I have learnt so much more about waste systems than I ever wanted to. In January, the system was blocked entirely. The previous owners had it emptied, but the company forgot to dig up the entry inspect point to clean it out. Result was that it got blocked. Once cleared, the relieved pressure of 50m of waste pipe full of “effluent” made an entertaining fountain. The slope of the garden ensured a good height to it. Glad it was raining that day :slight_smile:

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