TITLE 77: PUBLIC HEALTHHome
PART 890 ILLINOIS PLUMBING CODE
CHAPTER I: DEPARTMENT OF PUBLIC HEALTH
SECTION 890.1340 DETERMINATION OF SIZES FOR DRAINAGE SYSTEM
Section 890.1340 Determination of Sizes for Drainage System
a) Maximum Fixture Unit Load. The maximum number of drainage fixture units that may be connected to a given size of building drain, horizontal branch, or vertical soil or waste stack is given in Appendix A: Tables G and H.
b) Minimum Size of Building Drain, Horizontal Branches, Drainage Piping
1) The minimum size of any gravity building drain shall be four (4) inches in diameter.
2) Pressure building drains shall not be used where gravity drains may be installed. Pressure building drains shall be sized in accordance with the ejector pump manufacturer's recommendation but shall not be less than two (2) inches in diameter.
3) Gravity drained horizontal branches of the building drain shall be sized in accordance with Appendix A, Table H.
4) No portion of the drainage system installed underground or below a basement or cellar shall be less than two (2) inches in diameter.
5) The drainage piping shall not be reduced in size in the direction of flow.
c) Minimum Size of Soil and Waste Stacks. No soil or waste stack shall be smaller than the largest horizontal branch connected thereto except that a four (4) inch x three (3) inch water closet connection shall not be considered as a reduction in pipe size.
d) Waste Stacks Serving Kitchen Sinks. In one (1) or two (2) family dwellings in which the waste stack or vent receives the discharge of a kitchen-type sink and also serves as a vent for fixtures connected to the horizontal portion of the branch served by the waste stack, the minimum size of the waste stack up to the highest sink branch connection shall be two (2) inches in diameter. Above that point the size of the stack shall be governed by the total number of drainage fixture units vented by the stack. (See Appendix J: Illustration F.)
e) Future Fixtures. When provision is made for the future installation of fixtures, those provided for shall be considered in determining the required size of drain pipes and vent piping during initial construction. Piping provided for such future installation of fixtures shall be terminated with a plugged fitting or fittings at the stack so as to form no dead ends. In a multi-story building, when openings are roughed in for future fixtures below the uppermost level, properly sized vent piping shall be connected to the vent system and carried down to the appropriate lower level and be capped or plugged in an accessible location for venting of the future fixtures.