A mechanical engineering graduate student at the City College of New York, Artur Zych is looking to learn more about MEP engineering, so he visited ASPE Connect to ask our experts about the approved fittings for connecting horizontal branches to vertical stacks.
It’s always best to first check the model codes and the code in the jurisdiction in which you are working. When you initially become involved in plumbing design, Paul Baker, PE, CPD, GPD, recommends buying the most recent model code books with commentary to become familiar with the requirements and for easy reference. In this case, in the 2018 edition of the International Plumbing Code (IPC), Table 706.3 shows what fittings are allowed for each change in direction for sanitary drainage. This table is also included in the New York City Plumbing Code, with a few local modifications.
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TABLE 706.3. FITTINGS FOR CHANGE IN DIRECTION |
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|
TYPE OF FITTING PATTERN |
CHANGE IN DIRECTION |
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| Horizontal to vertical | Vertical to horizontal |
Horizontal to horizontal |
|
| Sixteenth bend |
X |
X |
X |
| Eighth bend |
X |
X |
X |
| Sixth bend |
X |
X |
X |
| Quarter bend |
X |
Xa |
Xa |
| Short sweep |
X |
Xa, b |
Xa |
| Long sweep |
X |
X |
X |
| Sanitary tee |
Xc |
¾ |
¾ |
| Wye |
X |
X |
X |
| Combination wye and eighth bend |
X |
X |
X |
| For SI: 1 inch = 25.4 mm a. The fittings shall only be permitted for a 2-inch or smaller fixture drain. b. 3 inches or larger. c. For a limitation on double sanitary tees, see Section 706.3. Source: New York City Plumbing Code |
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However, the codes only provide the minimum requirements, so guidance is needed to learn good engineering design practices, which is why it’s always beneficial to reach out to those who have experience in the industry, such as our experts on ASPE Connect.
The Best Option for Connecting Horizontal Branches to Stacks
Many prefer to connect using a sanitary tee because they take up less space than other types of fittings and they seldom present issues protruding from the wall/ceiling connection (combination fittings have a much longer sweep), says James Richardson, CPD.
When you are dealing with waste traveling downward vertically or waste traveling horizontally, James continues, you must use a directional pattern fitting such as a wye or a combination wye and eighth bend because you literally have to tell the waste which direction to go. When waste is traveling from a horizontal direction to a vertical direction, a directional pattern fitting isn’t necessary because gravity tell the waste where to go.
For stacked apartments, if you are using cast iron pipe, Charlotte Pipe makes appropriate fittings for this application, Paul Baker says.
What About Vent Connections?
If the stack also serves as the vent (waste stack vent systems), using a combination fitting creates a code compliance issue with IPC Section 909.2, as it puts the “vent connection” below the weir of the trap, according to James.
Do you have more advice? You can share your knowledge on this topic in the discussion thread on the ASPE Open Forum.
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