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Scaffold load classes, platform width and plank overhang compared
Quick answer: OSHA light 25, medium 50, heavy 75 lb/ft². BS EN 12811-1 classes 1 to 6: 0.75, 1.5, 2.0, 3.0, 4.5 and 6.0 kN/m². Saudi Aramco CSM light 120, medium 240 kg/m². The same job can sit in a different class under each one.
Side by side
Each value with the document it comes from.
| Requirement | OSHA 1926 Subpart L USA | BS EN 12811-1 · TG20 UK and Europe | Saudi Aramco CSM · GI 8.001 Saudi Aramco sites |
|---|---|---|---|
| Duty or load class | Light 25 · medium 50 · heavy 75 lb/ft²About 1.2 · 2.4 · 3.6 kN/m². Guidance in the non-mandatory Appendix A.29 CFR 1926 Subpart L, Appendix A (1)(c) | Classes 1–6: 0.75 · 1.5 · 2.0 · 3.0 · 4.5 · 6.0 kN/m²TG20 covers classes 1 to 4; classes 5 and 6 need a specific design.BS EN 12811-1:2003 6.1.3 Table 3; NASC TG20:13 Operational Guide 6.2 | Light 120 · medium 240 kg/m²25 · 50 lb/ft². Above 240 kg/m² the scaffold is special duty.CSM II-2 §2.5.1 E |
| Minimum platform width | 18 in (46 cm)12 in (30 cm) for ladder jack, top plate bracket, roof bracket and pump jack scaffolds.29 CFR 1926.451(b)(2) | Width classes W06 to W24W06 is 0.6 m to under 0.9 m of clear width; only 30 mm of the toe board counts. At least 600 mm clear between standards.BS EN 12811-1:2003 5.2, Table 1 | — |
| Plank or board overhang | At least 6 in; at most 12 inPast the support centreline, unless cleated or hooked. Up to 18 in when the platform is longer than 10 ft.29 CFR 1926.451(b)(4), (b)(5) | At least 50 mm; at most 4 × board thicknessAbout 150 mm for 38 mm boards.NASC TG20:13 Design Guide 2.1.8.3, Table 2.4 (check TG20:21) | At least 150 mm; at most 300 mmPast the end bearer centreline, unless cleated or restrained.CSM II-2 §2.5.6 G–H |
| Gaps in the deck | 1 in or lessBetween planks and between the platform and the uprights, unless a wider gap is shown to be necessary.29 CFR 1926.451(b)(1)(i) | — | Over 50 mm: cover itGaps from 50 mm to 600 mm are covered with exterior plywood at least 20 mm thick, lapped at least 300 mm on both sides.CSM II-2 §2.5.6 M |
Summary for learning, checked on 24 October 2026. Values as written in the documents named, as used in the AL-YASSIN question banks. TG20 values are from TG20:13; check TG20:21. Verify against the latest edition and your project's own rules before you use any figure. AL-YASSIN is independent and is not endorsed by OSHA, BSI, NASC or Saudi Aramco. — means the document does not give it as one figure here.
Mistakes we see in our exams
- Assuming masonry is medium duty without adding up the load. A few more blocks on the bay can make it heavy duty.
- Using 1.2 m transoms for TG20 load class 4. Class 4 boards need transoms at 0.9 m.
- Counting the whole toe board in the BS EN 12811-1 width class. Only 30 mm of it counts.
- Building a class 5 scaffold off a TG20 sheet. TG20 stops at class 4; class 5 and 6 need a specific design.
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Questions
What are the BS EN 12811-1 load classes?
Six service load classes: 0.75, 1.5, 2.0, 3.0, 4.5 and 6.0 kN/m² for classes 1 to 6 (BS EN 12811-1 Table 3). TG20 covers classes 1 to 4. Verify against the latest edition.
What are light, medium and heavy duty scaffolds under OSHA?
The non-mandatory Appendix A to Subpart L uses 25, 50 and 75 lb/ft² for light, medium and heavy duty. Verify against the current eCFR.
What is the minimum scaffold platform width under OSHA?
18 inches (46 cm), or 12 inches (30 cm) for ladder jack, top plate bracket, roof bracket and pump jack scaffolds. 29 CFR 1926.451(b)(2). Verify against the current eCFR.
What duty ratings does Saudi Aramco use for scaffolds?
Light duty 120 kg/m² (25 psf), medium duty 240 kg/m² (50 psf); above that is special duty. CSM II-2 §2.5.1 E. Verify against the latest edition.