running toilet waste pipe inside stud wall.

[Jonathan Sutton]

Renovating an upstairs bathroom. Void between floor boards and ceiling below is too narrow to hide the waste pipe from a wall hanging toilet.

My plan is to build stud wall with sufficient width to hide the 100mm toilet waste pipe into the existing stack. In practice this means extending the existing toilet waste pipe about 1.5 meters.

Two questions:

Can I reduce the 100mm waste pipe to 90mm?
Are there any [pooh] traps or problems with doing this?



This is an onsuite bathroom, we a detached property and the stud wall exists already. None of family have particularly ruffage rich diets..

 

[ShaunCorbs]

Need a 2x6 wall and no you can’t don’t think they even make 90mm waste / soil

 

[Ben-gee]

Soil pipe is 110mm in uk, geberit etc do make 90mm soil pipe and this is indeed what comes with there wallhung frames -along with an adapter to go up to our 110.
I see no reason why you couldn’t get a length of this 90mm and run it to the existing 110mm stack. I wouldn’t include any bends though.

Obviously it is more likely to block than 110, and I would always run a wc in 110 myself.

I have seen toilets on 3” pipe, this is 82mm, and they worked fine (only one per branch to a bigger 110 stack). However I believe the pans were designed for this.

Why not just do it in 110?