Toilet plumbing fall: Running pipe across concrete roof

[craigiecraigie4]

Hi guys,

I've searched the forum, and I've read that the gradient (fall) of a toilet (WC) discharge should be between 0.25/12 and 0.125/12 (from 1/4" per foot). Apparently this is sufficient to assure flow, yet not so steep as to allow water to flow and leave solids behind.

My issues is that I am building a new bathroom on top of a ground floor with a 480mm reinforced concrete roof. There is NO chance of cutting tho this roof - not even drilling without diamind tips! It is thus imperative that I am able to take a discharge pipe around 11m across this roof. My understanding is that it is sufficient if the end of this pipe is 0.25m above the roof, and the other end at the level of the roof. I have 3 questions:

• Is this 0.25/12 correct? It sounds awfully low to assure one that the pipe will truly empty and that solids will not accumulate
• At the endge of the roof, this pipe will drop vertically into the main sewer line (which is pretty close to the edge of the house). Is this vertical drop an issue given the "not too steep" rule?
• Finally, what diameter should such a pipe be?

Great forum!

 

[corgiman]

[Is this 0.25/12 correct? It sounds awfully low to assure one that the pipe will truly empty and that solids will not accumulate

I always go by 4" = 1mtr drop in 40 mtrs so thats about right

[*]At the endge of the roof, this pipe will drop vertically into the main sewer line (which is pretty close to the edge of the house). Is this vertical drop an issue given the "not too steep" rule?

dont be silly!unless you and yours are going to produce something that defies gravity then there is no chance of anysolids being left behind is there

[*]Finally, what diameter should such a pipe be?


4" would be the best.

 

[craigiecraigie4]

Thanks corgiman