Soil and Waste advice - New extension

27 May 2004
Reaction score
United Kingdom
Appologies in advance for what will probably be a lengthy post:-

First I am looking for advice on building a new soil stack in an extension, it is a 2 storey extension with WC and Basin on the Ground floor and WC, Basin and shower on the 1st Floor. Soil stack goes into a new 110mm soil pipe fitted by the builders underground (BCO Has approved it)
The Builders will be providing a hole in the roof with a 110mm pipe ready installed for venting.
I have designed the extension so that the two rooms are directly above each other and share the internal soil stack.

How do I go about designing/building the stack from scratch and linking the various soil and waste pipes into it, allowing for the correct falls in the pipes and and minimum distances the inlets have to be apart?
Sponsored Links
first look at where you want the loos and to sit in their respective rooms. the closer they are to the stack the better.

you can either position the toilets so that they discharge directly into the stack branch. for this to work you need to be fairly accurate with the holes in the walls and the toilet positions will be pretty rigid.

or you can off set the toilet from the stack and have a 90deg bend, out of the wall and into the stack branch. there is slightly more flexibility with this method.

the rest of the 38mm and 32mm waste pipes can be bossed onto the stack wherever deemed necessary.

try and orientate the shower waste so that it is near to the outside wall, as the opportunities for gaining fall will be less with the shower as the waste is very low to begin with.
Waste stack runs up corner of WC Room and shower room above. Toilets have been purposely been put on wall next to soil stack (Max 500mm away from stack with 1 x 90 degree bend)

Shower is on inside wall, however the floor joists run in the right direction to allow me to run betwen them to achieve the desired fall.

Do I need to use boss's or are there pre-made joins I can use to feed the waste pipes in and what about limitations on how close they can be together?
Paul_Thomas said:
Do I need to use boss's or are there pre-made joins I can use to feed the waste pipes in and what about limitations on how close they can be together?

you can use either pre-made knock outs with a rubber spigot insert or the strap-on boss method. i'm not a fan of seeing wastes inserted into the stack directly opposite each other, although it is only proximity of the bosses that dictates distance apart (vertically).

in my previous post i misunderstood the fact it is an internal stack and not external. apologies apart, the principals are still the same.
Sponsored Links

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local