We are putting a shower room into our attic with toilet, sink and shower.

Due to height restrictions in the attic the shower tray can't be raised enough to have the shower waste pipe go out the side wall so it needs to go down through the house and out the back. Our builder then recommends that we have the toilet waste go down the same route through the house so he can feed the shower waste pipe into it.

We didn't like the sound of having the toilet waste go through the house so suggested having it go out the side of the house (which is possible). However, he says that this means that the shower waste pipe will have to be very long (because it will have to go all the way down through the house and out the back before it meets the main drain) and this can cause the water in the p-trap to be sucked out which means we will have smells of the drain coming up to the shower room.

I was wondering is this the case - if the shower waste pipe is very long (because it doesn't join up to the toilet waste soon enough) is there the risk that the water might be sucked out of the p-trap creating smells in the shower room?

Many thanks for any help.

Hi TriciB and welcome to AMHD. I'm sure an expert will be along shortly to answer, in the mean time I would think if the shower is properly vented you shouldn't have a problem. I think I would question the plumber a little closer. Good luck and hang in there a few for an expert.

Agree with Parttime, if the shower is properly vented I see no issue with dropping it into the lower floors... shouldn't be an issue.

However, you said, "We didn't like the sound of having the toilet waste go through the house..."

Can you tell me why that is? See here, most homes have the main toilet drain pipe running through the house in different ways/different paths with absolutely no issues, so there shouldn't really be any concerns in terms of running drainage through the house.

Let us know more here, OK?

Mark

If wet vents, (see image) are allowed in your area why the long shower drain?
And like Mark, I'm curious as to why the drainage has to go out side. Would that be easier then taking it through the house? How about the water? Back to you, Tom

Are you located in USA?

Good pickup by HKS. In Britain and Ireland, almost all of the main stacks run outside the house. Not sure why but quite common to see pipes running down the outside walls.

Hi everybody, thanks for all your help. I think we are going to run the toilet pipe out the side of the house and add a vent to the shower pipe to prevent any smells coming into the bathroom.

Harold - we live in Ireland

Mark - below the attic we are dividing the master bedroom into two smaller bedrooms for our young boys. Currently the toilet pipe is to be hidden in the partition wall. Our concern is that we might one day want to restore the room back to its original size, but if we do we would have a great big toilet pipe running through the middle of it. We are also worried that it might be quite noisy in these rooms every time we flush the loo.

Many thanks again everyone
TriciB