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Trade Exam · Module 4

Toilet Installation: Flanges, Clearances and Flushing Devices

Lesson 6 of 9~20 minFree previewCurrent as of September 2026Leer en español

Setting a water closet to the 2025 California Plumbing Code: the flange sits on top of the finished floor, 15 inches from center to any side wall and 30 inches between fixtures with 24 inches of clear space in front, corrosion-resistant bolts, a 3 inch trap and trap arm, an antisiphon fill valve with its critical level 1 inch above the overflow, and a maximum effective flush of 1.28 gallons. What the code leaves to the manufacturer (rough-in distance, wax or waxless seal, bolt torque) is covered as practice, not code.

Key Takeaways

  • CPC 402.6: the bottom of the closet flange is set on top of the finished floor, and the bowl is bolted with an approved gasket, washer or setting compound.
  • CPC 402.5: at least 15 inches from the water closet's center to a side wall or obstruction, 30 inches center to center, and 24 inches of clear space in front.
  • CPC 402.3 and 402.6.2: the bowl and flange are secured with copper alloy, copper or other listed corrosion-resistant screws and bolts.
  • CPC 411.2: the effective flush volume of a water closet may not exceed 1.28 gallons; dual flush is the average of two reduced flushes and one full flush.
  • CPC 413.3 and 603.5.2: a flush tank has an antisiphon fill valve to ASSE 1002 with its critical level at least 1 inch above the full opening of the overflow pipe.
  • CPC 603.5.1: a flushometer valve's atmospheric vacuum breaker is on the discharge side, at least 6 inches above the bowl's overflow rim.
  • Table 702.1: a water closet needs a 3 inch minimum trap and trap arm; Table 1002.2 note 2 limits its trap arm to 6 feet from the flange face to the vent.
  • The rough-in distance from the wall is set by the fixture's manufacturer, not by the CPC.

Why This Matters

A water closet looks like the simplest fixture in the house, but the code packs a lot into it: flange height, fasteners, clearances, flush volume, backflow protection on the fill valve, and the size of the drain. This lesson collects every CPC rule for a water closet in one place, and marks clearly what the code leaves to the manufacturer.

The Closet Flange (CPC 402.6)

  • Approved connections: copper alloy, hard lead, ABS, PVC, or iron flanges that are caulked, soldered, solvent cemented, rubber-gasketed, or screwed to the drainage pipe.
  • The bowl is bolted to the flange with an approved gasket, washer, or setting compound between the fixture and the connection.
  • Height: the bottom of the flange is set on the top of the finished floor.
  • Size (402.6.1): about 7 inches in diameter, presenting a 1-1/2 inch wide face to receive the gasket or seal.
  • Caulked-on flanges: at least 1/4 inch thick and at least 2 inches in overall depth.
  • The closet bend or stub is cut off smooth and even with the top of the flange before the rough inspection.
  • Flanges are designed and secured to support the fixture.

Fasteners (402.3 and 402.6.2): floor-mounted fixtures are secured to the drainage connection and floor with copper, copper alloy, or other equally corrosion-resistant screws or bolts, sized and numbered to support the fixture.

Wall-mounted water closets (402.6): bolted to an approved carrier fitting that is attached to the structure, with a neoprene, felt, or similar approved gasket. Framing-affixed carriers for off-the-floor water closets with concealed tanks comply with ASME A112.6.2 (402.4).

Floor-mounted back-outlet bowls (402.6.3): set level with a 90 degree angle between floor and wall at the outlet centerline, with a flat mounting surface at least 5 inches to the right and left of the outlet centerline. Offset, eccentric, or reducing flanges are not permitted with these fixtures.

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