Swimming Pool (C-53) · Lesson 4 of 8

Pool Floor Slope, the 4-1/2 Foot Line, and Depth Markers

"Pool Floor Slope, the 4-1/2 Foot Line, and Depth Markers" is lesson 4 of 8 in the Swimming Pool (C-53) Learning Hub. It opens with "The Shape Comes From Figures 31B-1 to 31B-3" and works through 5 short steps, then a worked example you can check yourself against.

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Steps in this lesson

  1. The Shape Comes From Figures 31B-1 to 31B-3
  2. The 1-in-10 Rule
  3. The Depth Marking Line and Finish Colors
  4. Where the Depth Markers Go
  5. Marker Size, Position, and No-Diving Markers

The worked example in the course applies this lesson to a realistic job in 6 steps, from "Pick the table" through "Size and no-diving".

What you'll be able to do

  • Explain the main idea of "Pool Floor Slope, the 4-1/2 Foot Line, and Depth Markers" in plain language you can use on the exam.
  • Apply this step with confidence: "The Depth Marking Line and Finish Colors".
  • Apply this step with confidence: "Where the Depth Markers Go".
  • Apply this step with confidence: "Marker Size, Position, and No-Diving Markers".
  • Test yourself on the worked example and the quick-check quiz inside the classroom.
Floor Slope and Depth Markers30 ft x 50 ft public pool, 3'-0" to 6'-0" (section not to scale)water line4-1/2 ft depth line(tile 4 to 6 in. wide)run 15 ft3'-0"6'-0" maxslope per Fig. 31B-3depth markerSLOPE AND MARKERSSlope (3109B.3: max 1 ft in 10 ft)rise = 4'-6" - 3'-0" = 1.5 ftrun = 1.5 x 10 = 15 ft minimumPerimeter markers (3110B.4.1)perimeter = 2 x (30 + 50) = 160 ft160 / 25 = 6.4, round up = 7 markersMarker rules (3110B.4)numerals at least 4 in. highwithin 3 ft of the water, to nearest 6 in.Run at least 15 ft | tile line required | at least 7 markersMaximum depth 6'-0" is over 5 ft, so the 4-1/2 ft depth line is requiredDepth 6 ft or less: no-diving markers beside the depth markers2025 CBC §§3109B.3, 3110B.3, 3110B.4, 3110B.5 (Chapter 31B)CC
The diagram for this lesson, exactly as it appears in the Learning Hub.

The first steps of this lesson

Step 1: The Shape Comes From Figures 31B-1 to 31B-3

2025 CBC §3109B.1 says a public pool shall conform to Figures 31B-1 through 31B-7. A pool with no diving board uses Figure 31B-3 and Table 31B-3A when its maximum water depth is 6'-0" or less, and Table 31B-3B when it is deeper. The figure notes print a break in slope "located at a water depth equal to 4'-6"" (Figure 31B-3 note 4), and §3109B.2 allows a construction tolerance of not more than 2 inches on those dimensions.

Step 2: The 1-in-10 Rule

§3109B.3: any portion of a pool with a water depth of 4-1/2 feet or less shall have a uniform slope that does not exceed 1 foot of vertical in 10 feet of horizontal. The run you need is the rise times 10, or more; a flatter floor always passes, a steeper one never does. The same section requires a uniform water depth along the entire base of the stairs.

The remaining 3 steps, the worked example and the quiz are in the course. This is a preview. The full lesson, with the step-by-step explanations, a worked example and a quick-check quiz, is inside the classroom.

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