Frame and tube scaffolds are covered in the US by OSHA’s construction standard, 29 CFR 1926.451. Its best-known numbers are the 4:1 rule (a scaffold taller than four times its base width must be tied in), fall protection above 10 ft, platforms at least 18 in wide with gaps of 1 in or less, and 4 times the intended load as the strength requirement. This page lists the main requirements with their section numbers and has a calculator for when, and how often, a scaffold must be tied to the building.
OSHA scaffold requirements
| Topic | Requirement | 29 CFR section |
|---|---|---|
| Capacity | Each scaffold and component supports its own weight plus at least 4 times the maximum intended load | 1926.451(a)(1) |
| Planking | Each working platform fully planked or decked; no more than 1 in between planks and between the platform and uprights | 1926.451(b)(1) |
| Platform width | At least 18 in (12 in for ladder jack, top plate bracket, roof bracket and pump jack scaffolds) | 1926.451(b)(2) |
| Distance to the work | Front edge no more than 14 in from the face of the work unless guardrails or personal fall arrest are used (3 in for outrigger, 18 in for plastering) | 1926.451(b)(3) |
| Plank ends | Over the centre of the support by at least 6 in; no more than 12 in overhang for planks 10 ft or shorter, 18 in for longer ones, unless designed or guarded | 1926.451(b)(4)-(5) |
| Overlaps | Only over supports and at least 12 in, unless nailed or otherwise restrained | 1926.451(b)(7) |
| Tipping (4:1) | Supported scaffolds taller than 4 times their narrowest base width must be tied, guyed or braced | 1926.451(c)(1) |
| Tie spacing | At the 4:1 height, then every 20 ft vertically (scaffolds 3 ft wide or less) or 26 ft (wider), at each end and every 30 ft horizontally; top tie within the 4:1 height of the top | 1926.451(c)(1)(ii) |
| Footing | Base plates and mud sills or another adequate firm foundation; no unstable objects (barrels, boxes, loose brick) as supports | 1926.451(c)(2) |
| Access | Ladder, stair tower, ramp or other safe access when the platform is more than 2 ft above or below the point of access; cross braces on frame scaffolds are not a means of access | 1926.451(e) |
| Fall protection | Required for each worker on a scaffold more than 10 ft above a lower level | 1926.451(g)(1) |
| Guardrail height | Top rail 38 to 45 in above the platform on supported scaffolds placed in service after January 1, 2000 (36 to 45 in before); midrail about halfway | 1926.451(g)(4)(ii), (iv) |
| Toeboards | Along platform edges more than 10 ft up where people below could be struck | 1926.451(h)(2)(ii) |
| Power lines | At least 10 ft from lines under 50 kV, more for higher voltages | 1926.451(f)(6) |
| Inspection | By a competent person before each shift and after anything that could affect it | 1926.451(f)(3) |
| Weather | No work during storms or high winds unless a competent person approves and workers have fall arrest or wind screens | 1926.451(f)(12) |
Scaffold tie calculator (4:1 rule)
Free-standing height and tie levels by base width
| Narrowest base width | Free-standing up to (4:1) | Second tie level, scaffold 3 ft wide or less | Second tie level, wider scaffold |
|---|---|---|---|
| 2-1/2 ft | 10 ft | 30 ft | 36 ft |
| 3 ft | 12 ft | 32 ft | 38 ft |
| 4 ft | 16 ft | 36 ft | 42 ft |
| 5 ft | 20 ft | 40 ft | 46 ft |
| 6 ft | 24 ft | 44 ft | 50 ft |
Planking: the numbers in practice
- A standard 2×10 or 2×12 scaffold plank 8 to 10 ft long can overhang its support by 6 to 12 in; a 12 or 16 ft plank by 6 to 18 in.
- Overlapped planks must lap at least 12 in over a support, or be cleated or nailed so they cannot slide.
- Gaps over 1 in are allowed only where the employer can show a wider space is needed, for example around uprights (1926.451(b)(1)(i)).
- Use scaffold-grade planks or fabricated planks rated by their maker (OSHA’s non-mandatory Appendix A to Subpart L describes scaffold-grade lumber); ordinary construction lumber of unknown grade is not a scaffold plank.
Homeowners
These rules bind employers, but they are a good checklist for anyone renting a few frames to paint a house: set the base plates on mud sills on firm ground, level the frames with screw jacks rather than blocks, plank the full width, put guardrails on anything over 10 ft, keep the height under four times the base unless it is tied to the house, and stay 10 ft from power lines. Rental companies supply the maker’s instructions; follow them.
Frequently asked questions
What is the 4 to 1 rule for scaffolding?
A supported scaffold taller than 4 times its narrowest base width must be restrained from tipping by ties, guys or braces (29 CFR 1926.451(c)(1)). A 5 ft wide base can stand free to 20 ft.
At what height does a scaffold need guardrails?
OSHA requires fall protection for anyone on a scaffold more than 10 ft above a lower level (1926.451(g)(1)); on supported scaffolds that is usually a guardrail with the top rail 38 to 45 in high.
How wide must a scaffold platform be?
At least 18 in for most scaffolds; 12 in for ladder jack, roof bracket, top plate bracket and pump jack scaffolds (1926.451(b)(2)).
How far can a scaffold plank overhang?
At least 6 in past the centre of the support, and no more than 12 in for planks 10 ft or shorter (18 in for longer planks) unless the overhang is designed to carry the load or guarded (1926.451(b)(4)-(5)).
Sources
- US federal regulations (29 CFR), read at law.cornell.edu; text cached 24 October 2026. Paraphrased with section numbers, not the legal text. 29 CFR 1926.451.
Last reviewed: 24 October 2026. Numbers in the tables are our arithmetic from the sources listed; code sections are summarised, not quoted. How we check our work: methodology and corrections. Spotted an error? Please let us know.