Another plumbing quandry...vent pipe !

[stan]

As you can see by the recent "calls for advice/assistance" posts that I am renovating a spare bathroom just now......

Today I decided to remove some old plasterboard from our second bathroom to see what the water piping was like behind..my thoughts being that a shower cubicle may be passed up in favour of a wetroom type set-up. As I removed an awkward bulging shaped bit of plasterboard from the corner at the window, I found a vertical 100mm pvc pipe which is connected via a T fitting to the soil pipe. This is, I am presuming, a vent stack to make waste water run to the septic tank without blocking up. (vacuums and all that !)

At present we have an old septic tank (just a concrete box in the ground) and are awaiting the artisan to fit a new conforming system with sand filter, ditch, outside vent pipes etc.

My questions are...1) do I need this particular vent pipe that I uncovered today?, given the fact that we are getting a new system, albeit the new vent pipes will be at the other side of the house and nowhere near where this pipe is. The bathroom is on the ground floor and the pipe seens to vent into a small space in the flat roof.  2) if I need to retain such a vent pipe, can I replace it with a narrower one, say 50mm diameter so I can re-frame the interior bathroom wall and have the new plasterboard flush, instead of bulging out from the framing? (see photos)

http://s1076.photobucket.com/albums/w454/stan6822/bathroom/

Again, any advice appreciated.

[sid]

I think that the vent pipe you have found will have to remain. It's there to allow air into the system when you flush the WC and otherwise the vacuum caused would suck the water out of the u-bends in the washbasins and baths/showers trays in the vicinity, (assuming that they're all connected to the same soil pipe), and possibly the WC itself and you'd get smells coming back up.

We had a new bathroom installed when we extended the house and the plumber installed a 100mm vent right at the end of the pipe run, ie beyond the WC at the point furthest from the fosse. Ours vents (outside through the wall) on a short vertical stack at about 1m above the level of the WC and has a membrane valve on it so that air can only enter, not exit.

Your new foss will have a vent but that's for the gases from the fosse and won't help this problem.

I think I would have been inclined to make short stack outside through the wall just below floor level, but it looks a bit late for that now with your floor tiling and plasterboarding somewhat advanced. I'm not convinced that a smaller diameter pipe would be sufficient. You'd need FOUR 50mm pipes to get the same volume.

Let's wait and see what others suggest.

[stan]

[quote user="sid"]

I think that the vent pipe you have found will have to remain. It's there to allow air into the system when you flush the WC and otherwise the vacuum caused would suck the water out of the u-bends in the washbasins and baths/showers trays in the vicinity, (assuming that they're all connected to the same soil pipe), and possibly the WC itself and you'd get smells coming back up.

We had a new bathroom installed when we extended the house and the plumber installed a 100mm vent right at the end of the pipe run, ie beyond the WC at the point furthest from the fosse. Ours vents (outside through the wall) on a short vertical stack at about 1m above the level of the WC and has a membrane valve on it so that air can only enter, not exit.

Your new foss will have a vent but that's for the gases from the fosse and won't help this problem.

I think I would have been inclined to make short stack outside through the wall just below floor level, but it looks a bit late for that now with your floor tiling and plasterboarding somewhat advanced. I'm not convinced that a smaller diameter pipe would be sufficient. You'd need FOUR 50mm pipes to get the same volume.

Let's wait and see what others suggest.

[/quote]

Thanks for that sid, the short stack outside is an attractive option. BTW, that is old plasterboard and flooring in the pics.....its all coming up and out!

[BIG MAC]

Point to ponder...if bathrooms above ...if you have a blockage will your 'vent' be a behind the wall overflow as water backs up?

Does the pipe need to be there at all if you are on a short run to a chamber which is vented?

At least you should consider fitting a Durgo valve (Air admittance valve) at a higher point than the spill over level of your loo cistern...

[HoneySuckleDreams]

When i fitted a vent stack on the outside (far end of the pipe run to the fosse...there was another next to the fosse). French friends queried why I had put it on the outside.

Apparently, they go on the inside for "tax purposes",  i.e. it's obvious to the world and his mate that you have a bathroom if you put the stack on the outside, thereby incurring more tax (if they happen to drive by to inspect your property).

[stan]

[quote user="BIG MAC"]

Point to ponder...if bathrooms above ...if you have a blockage will your 'vent' be a behind the wall overflow as water backs up?

Does the pipe need to be there at all if you are on a short run to a chamber which is vented?

At least you should consider fitting a Durgo valve (Air admittance valve) at a higher point than the spill over level of your loo cistern...

[/quote]

This particular bathroom has nothing above it..it is an "add on" to the main house, ie it has a flat roof above. The main bathroom is on the first floor at the other end of the main house, and strangeley enough does not have a vent stack like this.

The soil piping from the bathroom concerned runs outside at the base of the vent stack in the photos, about 10m , where it joins the soil pipe running from the upstairs bathroom, then runningm about 5m to the septic tank (which I have mentioned before, is to be replaced shortly). There is only the one vent stack for the whole system.

What I am considering (and please correct me if it sounds rubbish !), is to remove and cap the vent stack at floor level inside the bathroom and dig a hole outside where the pipe runs out, and towards the septic tank. Then I would cut the pipe and insert a T fitting and bring  a new vent stack vertically and against the outside wall, just short of the guttering and cap it with an "aerateur à membrane pvc" (as per page 117 of the Bricoman catalogue €39,90 - if that is a Durgo valve, BigMac?).

Does that sound about right?