Colorado Journeyworker Plumber — IPC 2024 — Chapter 9: Isometric Analysis

Isometric analysis: where does the code require a cleanout?

The isometric shows the drainage piping of a two-story dwelling. No cleanout is shown anywhere. Under the IPC, at which of the labelled points is a cleanout required?

Isometric (30-degree) line drawing of the drainage piping of a two-story dwelling. A 4-inch soil stack rises vertically from its base, through the second floor, and out through the roof as a vent. The building drain leaves the base of that stack and runs horizontally towards the building sewer, and it is labelled at four points: at D the vertical soil stack turns into the horizontal building drain; at C the drain drops to a lower elevation (the pipe keeps the same direction in plan); at B the drain is offset 22.5 degrees in plan; and at A the drain turns 90 degrees in plan, after which it leaves the drawing towards the building sewer (dashed continuation labelled "to building sewer"). A water closet and a lavatory discharge into the stack on the second floor, and a kitchen sink and a laundry tray discharge into it on the first floor. No cleanout is drawn anywhere on the drainage piping.
Figure 1 — Drainage (DWV) isometric of a two-story dwelling: 4-inch soil stack vented through the roof, building drain to the building sewer, and four labelled points A, B, C and D. Not to scale.
  1. A. A — where the building drain changes horizontal direction 90 degreesCorrect answer
  2. B. B — where the building drain makes a 22.5-degree horizontal offset
  3. C. C — where the building drain drops to a lower elevation
  4. D. D — where the vertical soil stack turns into the horizontal building drain

Why

IPC 708.1.4 requires a cleanout where a horizontal drainage pipe, building drain or building sewer changes horizontal direction more than 45 degrees (45 degrees or less is permitted without one). Point A is that fitting: the building drain turns 90 degrees in plan, so the cleanout belongs there. Point B is only a 22.5-degree offset in plan — not more than 45 degrees, so 708.1.4 adds nothing. Point C changes the elevation of the drain, not its horizontal direction: the pipe keeps running the same way in plan. Point D is the turn from the vertical soil stack into the horizontal building drain — again not a change of horizontal direction, and the same is true of any other vertical-to-horizontal turn. The interval rule of IPC 708.1.1 does not require a cleanout here either: the whole run shown is far shorter than the 100-foot interval it sets, and the 708.1.3 cleanout at the junction of the building drain and the building sewer is not on this sheet (the sewer leaves the drawing).

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