Code Applied by the app plumb.vent.trap-protection
Venting protects every trap seal
The drainage system carries vent piping that lets air in and out, so no fixture trap sees more than 1 inch of water column of pressure difference and no seal siphons out when the fixture upstream drains.
| When | The app uses |
|---|---|
| each fixture trap | protected by a vent |
| pressure difference at a trap seal, at most | 1 in w.c. |
- Source
- IPC · 901.2 Trap seal protection · read the public text
- Editions checked
- 2018 · 2021
- Used by
- Courses
- Amendments
No state or local amendment to this rule is on file. Not on file means the model code as written — check your jurisdiction.
A model code the authority having jurisdiction adopts.
Water running down a drain pushes air ahead of it and pulls air behind it. Without a vent the pull would siphon the water out of the next trap downstream, and the push would blow sewer gas through it. So every trap has a vent behind it, a pipe that lets air in and out, and the code measures it by the pressure the seal may see.
On a bid the vent piping is in the walls and rarely on the plan: a riser or an isometric shows it, the floor plan shows only where a stack leaves through the roof (VTR, vent through roof). Count the VTRs, and price the vent pipe from the riser.
What the app does with it
Nothing yet: the app does not apply this rule. It is on a course card (the plumbing course, Chapter 4, "Which walls carry a vent stack?"), which has you count the VTR tags as a counter. The app does not size or check vent piping.
Verify against your edition
The ways to vent a trap (individual, common, wet, circuit, air admittance valves) and their limits are the rest of the IPC's Chapter 9, and a jurisdiction may restrict air admittance valves. The 1 inch of water column is 901.2 in the 2021 text. The Uniform Plumbing Code states the same aim with the same figure (its Chapter 9; not opened for this sign-off). Settled 2026-09-27 by Claude on the owner's delegation, from the dossier's research and the model code text; not checked against a printed book or a local amendment.
Cited by section, not reprinted: the code text belongs to its publisher. Company practice is not a rule here — it lives with your pricing.