G
gemwand
I am fitting a new toilet into an existing cast iron stack, but in a new position so the stack has been partially dismantled and I have the luxury of being able to design the falls any way I want.
Can anybody advise on what appropriate falls are? There are lots of recommendations, but not all compatible, and little hard information on why the recommendations are as they are.
The old BS toilet specification had an angle at the WC outlet of 14 degrees, that equates to a fall near the outlet of about 1 in 4.
The standard soil stack branch is at an angle of 92.5 degrees, i.e. a slope in the branch of 2.5 degrees. This seems to be linked to one of the standard rules of thumb, half an inch fall for every foot of pipe (imperial), or 1 in 25 (metric).
Another rule of thumb is a fall of 1 in 40, which derives from Maguire's rule for self-cleansing in drain pipes with intermittent flow (fall = radius in mm/2.5).
The new BS 5503 has horizontal WC outlets. The part H building regulations give a fall of between 18mm and 90mm per metre for branch discharge pipes.
I believe that the old standard installations were designed to have a relatively rapid fall (1 in 4) from the WC outlet into to the soil branch, followed by a bend and then a shallower 1 in 24 fall to the main stack.
Can anyone say what (if anything) was wrong with that? Why do people now appear to recommend much shallower falls, particularly from the WC outlet?
Can anybody advise on what appropriate falls are? There are lots of recommendations, but not all compatible, and little hard information on why the recommendations are as they are.
The old BS toilet specification had an angle at the WC outlet of 14 degrees, that equates to a fall near the outlet of about 1 in 4.
The standard soil stack branch is at an angle of 92.5 degrees, i.e. a slope in the branch of 2.5 degrees. This seems to be linked to one of the standard rules of thumb, half an inch fall for every foot of pipe (imperial), or 1 in 25 (metric).
Another rule of thumb is a fall of 1 in 40, which derives from Maguire's rule for self-cleansing in drain pipes with intermittent flow (fall = radius in mm/2.5).
The new BS 5503 has horizontal WC outlets. The part H building regulations give a fall of between 18mm and 90mm per metre for branch discharge pipes.
I believe that the old standard installations were designed to have a relatively rapid fall (1 in 4) from the WC outlet into to the soil branch, followed by a bend and then a shallower 1 in 24 fall to the main stack.
Can anyone say what (if anything) was wrong with that? Why do people now appear to recommend much shallower falls, particularly from the WC outlet?
