Omission of relief vent for waste stack?

[John McMullen]

This question is about waste stacks and and relief vent connections at the base of the stack.

The situation is a toilet only waste stack and vent stack that is 5 stories tall. There is a dedicated 2" vent stack and 4" waste stack for these toilets (10 DFU residential toilets). First section 907 of the 2015 IPC mentions relief vent connections for horizontal offsets for waste stacks 5 stories or more.

However, 711.2.1 and 711.3 over ride the requirement for a vent connection at the stack base though. As long as the waste stack piping is sized at 1 size greater than requirements for a building drain (Which it is at 4"), no relief vent at the base of the stack is required. The concept is that over sized stacks minimizes any positive pressure developed by slugs going down the stack.

Another aspect of this, is these toilet stacks terminate in a parking garage space above ground. They turn horizontal and are connected to nearby bathroom lav and shower waste stack vents. Some of these lav and shower stacks might be 3-4 feet away from the toilet stacks. All these collect and route down columns in the garage then go below grade. This is the only thing I'm not sure about with this - I don't know if these lav stacks or shower stacks qualify as "horizontal branch connections" downstream of the lowest toilet stack offset. It does't define this aspect of it. But still, the toilet waste stack is 4", so the thought is pressure developed would be minimized because of that over sized waste stack.

See attached document with code sections and diagrams. Do you believe that no relief vent connection is required for this situation?

Thanks for any input. Venting is most obscure, hard to interpret part of plumbing

 

[frodo]

all you do is tie the vent stack into the waste stack at 42'' aff on the 5th floor


YOKE VENT. A pipe connecting upward from a soil or waste stack to a vent stack for the purpose of preventing pressure changes in the stacks.




904.2 Vent Stack Required Required

A vent stack shall be required for every drainage stack that has five branch intervals or more.

Exception Exception: Drainage stacks installed in accordance with Section 913.

Section 913 Waste Stack Vent



913.1 Waste Stack Vent Permitted if it does not meet these requirements, then a vent stack is required

A waste stack shall be considered a vent for all of the fixtures discharging to the stack where installed in accordance with the requirements of this section.

913.2 Stack Installation

The waste stack shall be vertical, and both horizontal and vertical offsets shall be prohibited between the lowest fixture drain connection and the highest fixture drain connection. Fixture drains shall connect separately to the waste stack. The stack shall not receive the discharge of water closets or urinals .

913.3 Stack Vent you said your vent stack is 2'' and your waste is 4''

A stack vent shall be provided for the waste stack. The size of the stack vent shall be not less than the size of the waste stack Offsets shall be permitted in the stack vent, shall be located not less than 6 inches (152 mm) above the flood level of the highest fixture and shall be in accordance with Section 905.2. The stack vent shall be permitted to connect with other stack vents and vent stacks in accordance with Section 904.5.

913.4 Waste Stack Size

The waste stack shall be sized based on the total discharge to the stack and the discharge within a branch interval in accordance with Table 913.4. The waste stack shall be the same size throughout its length.

code is clear, you are requird to have a vent stack and a yoke vent is required on the fith floor
you are aware that a 5 story building has to be cast iron right?