Design & installation of the single stack in Philadelphia Survey

The following series of questions apply to the observed experience of the poll taker regarding the design and installation of Single Stack Vent System or the Philadelphia Single-Stack Waste and Vent System. The scope does not include any consideration to the Sovent system, which uses special aerator branch tee fittings and dearator fittings. This poll is part of a research effort on how single-stack systems are used throughout the world. The research paper will be presented at the CIB W062 International Water Supply and Drainage Symposium in August 2023 in Leuven, Belgium. As the Philadelphia Single-Stack Waste and Vent System is likely the first documented implementation of the single-stack system and remains uncommon in much of the US, the feedback from ASPE Philadelphia is incredibly valuable to this research effort. Many thanks in advance!

John Lansing, CPD, LEED Green Associate

ASPE Portland

1.How often is the single stack vent system or the Philadelphia single stack used in Philadelphia, provided the fixture layouts are compatible with the branch to stack length requirements?

Frequently (more than 75% of the time)

Sometimes where applicable (25-75% of the time)

Not very often for new construction (less than 25% of the time)

2.For the stack base (vertical to horizontal transition), what fitting do you typically see used?

Always a single long sweep bend

Mostly a single long sweep bend, but sometimes a short sweep bend

Mostly two 45° bends with a short segment of pipe between

Sweep bends, two 45° fittings, or a combination wye are very common installation approaches

3.For stacks extending beyond 5 stories, is it common to provide a parallel vent stack? Assume there are no horizontal offsets in the stack.

Never – this does not align with the intent of the single stack drainage system

Never – though this is technically required even for single-stacks

Sometimes

Always. This is required by Section P-919.3.3 and Section 904.2

4.The IPC version of the single-stack drainage system requires the lowest 2 floors to discharge separately from stacks greater than 3 branch intervals in height. The Philadelphia Plumbing Code however does not feature this requirement in Section P-919 Philadelphia Single-Stack Waste and Vent System. How is this approached in Philadelphia?

A. The lowest 2 floors drain to a separate single-stack and the vent from that stack is extended to outside

B. The lowest 2 floors drain to a separate single-stack and the vent from that stack is provided with an air admittance valve

C. All fixtures connect directly to the stack and do not have individual vent piping, including the fixtures at the lowest levels

D. Both A and B

Other (please specify)

6.What fittings are most often used for branch connections to the stack

Sanitary Tee

Sanitary wye or combination wye

Both A and C are used about the same frequency

7.Are velocity breaks (a configuration using (4) 45° bends) often installed in the drainage stack?
Velocity Breaker

Yes, but only for buildings 30 stories and taller as required by the Philadelphia Plumbing Code

Yes, even in buildings below 30 stories

No, this is often ignored due to the negative airflow interference of airflow within the drainage stack

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