13-13 Reducers

Question: 13-13Code Section: 7Date: 30 September 2013OBC Reference:

Question Submitted: I am connecting a three piece washroom to a 4” building drain. There is approximately 16 feet between the washroom group and the 4” building drain. I was told that I could not use a 4”x3” reducer near the bathroom group but had to run 3” all the way to the “Y” connection at the building drain. Are reducers no longer legal?

Interpretation: This type of installation is a common occurrence in basements located in residential type dwelling units. The usual reason is for cost effectiveness (PVC vs ABS), but also where depth issues may be present given the 1:100 minimum for 4” drainage piping to 1:50 minimum for 3” piping.
It was agreed that there is nothing wrong with this installation as long as there is proper fall, the drains and vents sized accordingly and the area of turbulence (1.5m from base of stack) is adhered to.
The reducer fitting shall conform to the requirements set out in and