Lumber for Scaffolding

Scaffolding is common on the jobsite, but it’s especially on peoples’ minds with OSHA’s new fall protection regulations. The number one cause of scaffold accidents is the planking giving way. Training workers how to properly construct scaffolds (and use the correct material) is the key to avoiding these kinds of accidents.

Question

For scaffolding, can 2x10s be used in lieu of scaffold-grade planks?

Answer

No, 2x10s and other lumber commonly used for trusses are not sufficient for scaffolding applications. Only scaffold-grade lumber should be used for erecting scaffolds. 29 CFR 1926 Subpart L is OSHA’s standard for scaffolding, which is available at osha.gov. The standard defines a scaffold as, “any temporary elevated platform (supported or suspended) and its supporting structure (including points of anchorage), used for supporting employees or materials or both.”

Lumber designated as scaffold-grade meets a number of particularly high standards, which most construction-grade lumber does not meet. For instance, construction lumber only has two-thirds the capacity of scaffold-grade lumber. Construction lumber is not intended to withstand the forces likely to occur in a scaffold assembly. In addition, construction lumber is also cut to nominal sizes, so a 2x10 isn’t literally 2 in by 10 in. Table 1 compares the allowable spans for nominal and solid sawn wood planks.

Scaffold-grade lumber satisfies specific strength criteria determined by the grading rules for that particular species of lumber. These grading rules are set by a recognized lumber grading association or an independent lumber inspection agency and meet the minimum requirements set forth in OSHA standard 29 CFR 1926. As such, all scaffold-grade planks should be marked as scaffold lumber with the agency or association’s grade stamp.

One question that could be asked is: What if the design calculations for a specific loading situation indicate that No. 2 2x10 could work for scaffolding? Beware—even if the numbers suggest No. 2 might work, there are still significant differences between a No. 2 grade of lumber and scaffold grade. The lumber characteristics required for scaffold grade are higher and more stringent than those for No. 2. For instance, scaffold grade lumber has a higher standard for number and size of knots permitted, as well as slope of grain. In addition, while a No. 2 grade allows for pith and juvenile wood, scaffold grade planks do not allow these characteristics because they could weaken the lumber. Scaffold planks are also available using LVL material, which through its manufacturing process, eliminates many standard dimension lumber characteristics that could reduce strength.

Of course, the purpose of these strict scaffolding standards is safety. Using the correct material to properly construct scaffolding helps maintain a safe and efficient jobsite. OSHA further requires that employers train any employees who work on scaffolding to help them recognize and mitigate hazards.

Editor’s Note: While there have been proposed changes by the Southern Pine Inspection Bureau (SPIB) for Southern Pine dimension lumber grading rules and design values, this article is based on the design values in place in the fall of 2011. These proposed SPIB changes also do not apply to scaffold grade Southern Pine given that the grading rules are different. It is interesting to note that scaffold grade lumber does not allow pith center or juvenile wood due to the impact on strength and safe performance. Regardless of any future changes, the concepts in this article also apply to other lumber grades, such as Douglas Fir-Larch No. 2.