Ornamental Metal (C-23) · Lesson 2 of 6

Guard Height and Baluster Spacing: The 4-Inch Sphere

"Guard Height and Baluster Spacing: The 4-Inch Sphere" is lesson 2 of 6 in the Ornamental Metal (C-23) Learning Hub. It opens with "When a Guard Is Required" and works through 5 short steps, then a worked example you can check yourself against.

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Steps in this lesson

  1. When a Guard Is Required
  2. Guard Height
  3. The 4-Inch Sphere and Its Exceptions
  4. Lay Out Balusters Between Posts
  5. Two Layout Traps

The worked example in the course applies this lesson to a realistic job in 5 steps, from "Clear distance between posts" through "Check the other openings".

What you'll be able to do

  • Explain the main idea of "Guard Height and Baluster Spacing: The 4-Inch Sphere" in plain language you can use on the exam.
  • Apply this step with confidence: "The 4-Inch Sphere and Its Exceptions".
  • Apply this step with confidence: "Lay Out Balusters Between Posts".
  • Apply this step with confidence: "Two Layout Traps".
  • Test yourself on the worked example and the quick-check quiz inside the classroom.
Guard Baluster Spacing: The 4-Inch SphereGuard elevation (not to scale)4 in sphere must not pass42 in min25 balusters, 26 gaps of 3-15/16 inBottom rail 3 in above floor (under 4 in)Posts 10 ft o.c., 2 in square postsClear between posts = 120 - 2 = 118 inBaluster = 5/8 in square = 0.625 inn greater than (118 - 4) / (0.625 + 4)n greater than 24.65, so n = 25Gap = (118 - 25 x 0.625) / 26Gap = 102.375 / 26 = 3.9375 inTry 24: (118 - 15) / 25 = 4.12 in FAILSGap must be LESS than 4 in (sphere passes at 4.00)3.9375 in < 4 in → 25 balusters pass the 4 in sphere test36 to 42 in band may be 4-3/8 in (CBC §1015.4 Exc. 1), but full-heightbalusters must still hold 4 in below 36 inSources: 2025 CBC §1015.2-1015.4; 2025 CRC R321.1.1-R321.1.3CC
The diagram for this lesson, exactly as it appears in the Learning Hub.

The first steps of this lesson

Step 1: When a Guard Is Required

2025 CBC Section 1015.2 requires guards along open-sided walking surfaces such as mezzanines, equipment platforms, aisles, stairs, ramps and landings that are more than 30 inches above the floor or grade below at any point within 36 inches horizontally of the open side, and at the perimeter of occupiable roofs. 2025 CRC Section R321.1.1 prints the same 30 inch and 36 inch test for houses and adds that insect screening is not a guard. Measure the drop at the worst point, not the average.

Step 2: Guard Height

2025 CBC Section 1015.3 requires guards at least 42 inches high, measured vertically from the adjacent walking surface or, on stairs, from the line connecting the nosings. In Group R-3 and inside Group R-2 dwelling units, guards on the open sides of stairs need only be 34 inches (CBC Section 1015.3 Exception 1 and CRC Section R321.1.2 Exception 1). Where the top of a stair guard also serves as the handrail, it must sit between 34 and 38 inches.

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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