Limited Specialty (D-Series) (C-61) · Lesson 5 of 6

D-39 Scaffolding: Duty Class, 4-to-1 Design Load and Plank Spans

"D-39 Scaffolding: Duty Class, 4-to-1 Design Load and Plank Spans" is lesson 5 of 6 in the Limited Specialty (D-Series) (C-61) Learning Hub. It opens with "What D-39 Erects and Which Order Applies" and works through 5 short steps, then a worked example you can check yourself against.

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Steps in this lesson

  1. What D-39 Erects and Which Order Applies
  2. Duty Classes and the 4-to-1 Design Rule - 8 CCR 1637(b)(2)
  3. Plank Spans - 8 CCR 1637(f)(2)(A)
  4. Overhang, Deflection and Nailing
  5. Planning Sequence

The worked example in the course applies this lesson to a realistic job in 6 steps, starting with "Number of spans and supports".

What you'll be able to do

  • Explain the main idea of "D-39 Scaffolding: Duty Class, 4-to-1 Design Load and Plank Spans" in plain language you can use on the exam.
  • Apply this step with confidence: "Plank Spans - 8 CCR 1637(f)(2)(A)".
  • Apply this step with confidence: "Overhang, Deflection and Nailing".
  • Apply this step with confidence: "Planning Sequence".
  • Test yourself on the worked example and the quick-check quiz inside the classroom.
D-39 SCAFFOLD DECK: SPANS AND LOADSMedium-duty wood scaffold, Douglas Fir 2 x 10 planksDECK PLAN: 30 FT MEDIUM-DUTYLight 25 psf: 2x10 spans 10 ftMedium 50 psf: 2x10 spans 8 ftHeavy 75 psf: 2x10 spans 7 ft7.5 ft7.5 ft7.5 ft7.5 ft4 spans, each under the 8 ft maximum30 ft platform, 5 ft wideOverhang 18 in max unless guarded or anchoredPLAN THE DECK (8 CCR 1637)1) Medium-duty = 50 psf working load2) 2x10 plank span at 50 psf: 8 ft3) 30 / 8 = 3.75, round up: 4 spans 5 supports, span 30 / 4 = 7.5 ft4) Load: 50 x (30 x 5) = 7,500 lb Design: own weight + 4 x 7,500 = own weight + 30,000 lb5) Sag limit: 7.5 x 12 / 60 = 1.5 in6) Post the working load at the jobHeavy-duty (75 psf, 7 ft): 30 / 7 = 4.29rounds up to 5 spans, 6 supportsRESULT: 5 supports, 7,500 lb working, 30,000 lb designSource: 8 CCR 1637(b)(2), (b)(6), (f)(2)(A), (g), (w); CSLB Get Licensed to Build, D-39.CC
The diagram for this lesson, exactly as it appears in the Learning Hub.

The first steps of this lesson

Step 1: What D-39 Erects and Which Order Applies

CSLB defines D-39 Scaffolding as erecting metal or wood scaffolding, including temporary sidewalk sheltered construction work barricades (CSLB, Get Licensed to Build, D-39). The load, plank and platform numbers for every scaffold come from Cal/OSHA Title 8, Construction Safety Orders, Section 1637 General Requirements (8 CCR 1637). Later sections (1640 light-duty pole scaffolds, 1644 metal scaffolds, and so on) add rules for each type, but the duty class and plank table in 1637 are the starting point for any deck you plan.

Step 2: Duty Classes and the 4-to-1 Design Rule - 8 CCR 1637(b)(2)

Each scaffold must be designed and built with a dead load safety factor so it supports, without failure, its own weight and 4 times the maximum intended working (live) load. The maximum intended working loads are: light-duty 25 pounds per square foot of work platform, medium-duty 50, heavy-duty 75, and special-duty more than 75 as determined by a qualified person or a registered California Civil Engineer; engineered scaffolds are determined by that engineer. A scaffold must never carry more than its maximum intended working load (1637(b)(3)), and that load must be posted at a conspicuous location at the jobsite or given to each supervisory employee (1637(b)(6)).

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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