Importance of Base Plates

Because a supported scaffold transmits the weight of its entire load to the surface on which it rests, the foundation of a scaffold is critical to its safety. A scaffold on an unstable surface or a surface that can't support the scaffold's weight endangers lives.

As you learned on the previous slide, supported scaffold poles, legs, posts, frames, and uprights must rest on base plates, mud sills, or other adequate firm foundations. This wording can be interpreted broadly to mean that a scaffold needs either a base plate below each leg or a mud sill or other adequate firm foundation. This is incorrect. In fact, two components are required below each scaffold leg: 1) a base plate, and 2) a mud sill or other adequate firm foundation. This is clarified by OSHA's compliance directive, CPL 02-01-023, for Subpart L, "Scaffolds." Paragraph K.3.b states that the regulations require the use of both base plates and mud sills or other adequate firm foundations.

The regulations also state that the footing must be level, sound, rigid, and capable of supporting the loaded scaffold without settling or displacement.

The only way to prevent settling or displacement is to make sure the load is spread out over a large enough area. It's not enough to use a plywood pad as this focuses the scaffold load onto a very small area and causes the leg to bite or sink into the wood. This kind of settling is very dangerous.

Even with a good quality grade of plywood, the leg will crush the wood fibers and create an indentation on the plywood. Even a small indentation can destabilize a scaffold and endanger lives. Using a base plate will distribute the leg load to a much larger area, typically about 6" by 6", or 36 square inches.

Placing a scaffold leg directly onto a concrete slab is also not allowed. While the compressive strength of concrete is much greater than a scaffold leg on plywood, it is still less than the typical capacities of scaffold legs. Always use base plates or screw jacks with base plates on all scaffolds.

To learn more about Scaffolding Safety visit our Construction Scaffolding Safety Online Training web page.