Section 890.1500  Installation of Wet Venting

a)         The following shall not be used to wet vent another fixture trap: water closets, washing machine connections, blowout urinals, or dishwashers.

b)         Two lavatories with 1¼-inch traps shall be considered a single fixture for the purpose of this Section.

c)         A vertical wet vent may be used for two fixtures set on the same floor level, but connecting at different levels in the stack, provided that the vertical wet vent/drain between the two traps is one pipe diameter larger than the upper fixture trap and that both drains conform to Appendix A.Table I.  (See Appendix K.Illustration P.)

d)         A horizontal wet vent may be used for two fixtures set on the same floor level with one fixture connecting upstream of the other fixture on the horizontal line, provided that the horizontal wet vent/drain between the two fixtures is one pipe diameter larger that the upstream fixture trap.  The vent connection shall be located between the traps, and each trap-to-vent distance shall be in accordance with Appendix A.Table I.  (See Appendix K.Illustration Q.)

e)         A vertical/horizontal wet vent may be used for two fixtures set on the same floor level with one fixture connecting to the vertical stack and one fixture connecting to the horizontal line, provided that the wet vent/drain is one pipe diameter larger than the upper fixture trap and the drains conform to Appendix A.Table I. (See Appendix K.Illustration R.)

f)         A single bathroom group of fixtures, consisting of a water closet, lavatory and a bathtub, shower or floor drain, may be installed with the drain from a lavatory serving as a wet vent for a bathtub, shower or floor drain and for the water closet, provided that:

1)         Not more than four DFUs drain into a 2-inch diameter wet vent; and

2)         The horizontal branch is a minimum of 2 inches and connects to the stack at the same level as the water closet drain. The horizontal branch may also connect to the water closet bend.  (See Appendix K.Illustration S.)

g)         Bathroom groups installed back-to-back consisting of two water closets, two lavatories, and two bathtubs, showers or floor drains may be installed without individual vents, provided that:

1)         The water closets are wasted to a proper vertical drainage fitting;

2)         The bathtubs, showers or floor drains connect to the stack at the same level as the water closets;

3)         The lavatories connect to the stack at the same level; and

4)         The vent is a minimum of 2 inches in diameter.  (See Appendix K.Illustration T.)

h)         When bathroom groups are connected to the same soil stack, the waste pipe from one or two lavatories may be used as a wet vent for one or two bathtubs or showers, provided that:

1)         The wet vent and its corresponding extension to the vent stack are 2 inches in diameter;

2)         Each water closet is provided with an individual dry vent or vertical common vent; and

3)         The vent stack is sized as given in Appendix A.Table J.  (See Appendix K.Illustrations U and V.)

i)          On the lower floors of a multi-story building, a water closet may be wet vented with a single lavatory in lieu of the requirements of Section 890.1470(h).

j)          Bathroom groups consisting of a water closet, lavatory, and bathtub or shower, connected to a stack by a separate branch, may wet vent the water closet and bathtub or shower with the lavatory, provided that:

1)         The water closet and bathtub/shower connect to the stack at the same level;

2)         The wet vent and its corresponding extension are a minimum of 2 inches in diameter; and

3)         A vent stack connects at or below the lowest fixture connection and is installed for a stack of this type.  (See Appendix K.Illustration W.)

(Source:  Amended at 38 Ill. Reg. 9940, effective April 24, 2014)