What’s in a Plank?

By David H. Glabe, P.E. / April 1, 2006

Planks are a vital component in scaffolds, as even the casual observer will notice.  Yet it appears that too many workers take this vital component a little too casually.  Planks and platforms consistently rank in the top 10 list of most frequently cited violations of standards.  So what’s the big deal?  You would think that everybody using a scaffold would particularly note what they are standing on—or in some cases what they are not standing on.  After all, there isn’t much backup for the user who suddenly loses the board holding him or her.  Let’s face it; once the board disappears, you’re going down.

So, what can be done to decrease those citations and the corresponding high number of serious injuries and even death?  Well, first of all, you can comply with the applicable standards.  They were written to address the hazards associated with the use of planks.  These standards can be found in both the OSHA construction industry standards and general industry standards.  The Construction Industry standards are more comprehensive than the general industry standards and will be used as the guideline for the remainder of this article.  A review of the standards shows that the platform standards can be classified into three main groups; strength, installation, and maintenance.

Plank Strength

The OSHA Construction Industry standards require that all scaffold components, including plank, have at least a 4 to 1 safety factor.  This means that the plank must be able to support four times what you are placing on it.  If you weigh 150 pounds, the plank you’re standing on must hold  4 times 150 pounds or 4600 pounds.  If you weigh 300 pounds, then the plank has to be able to support 1200 pounds.  These same standards allow you to use whatever you want as a plank as long as you have the correct safety factor.  The OSHA General Industry Standards, on the other hand, specify that all wood plank shall be “scaffold grade” or equivalent.  The idea here was to instill some sense of strength for those workers who are unaware of the strength requirements.  Going back to the Construction Industry standards, it is interesting to note that no plank size or specie of wood is specified.  For that matter, there is no reference to wood!  You get to use whatever you want as long as it’s strong enough.  Now, before I offend the purveyors of plank, please remember that the use of scaffold grade plank or equal is a good idea since most workers are used to it and have an idea how much load they can put on it.  It’s just that OSHA can’t write you up for not having non-scaffold grade plank.


It is expected that plank will be installed on a scaffold in such a way that it will remain in that location and will present a reasonable surface from which to work.  To guarantee that expectation, the standards establish minimum criteria for the construction of plank platforms.  First it is assumed that you are using a wood product that is about 2 inches thick by 10 inches wide.  Second, you will be using multiple plank to construct your platform, and third, the plank will result in a relatively level surface.  Here are the criteria to make the safe platform happen:

  1. The ends of the plank shall overhang its’ supports at least 6 inches, or in the alternative, be restrained so it doesn’t come off the supports.  It is assumed that if the plank overhangs the support 6 inches, it won’t slip off.
  2. The maximum overhang is 12 inches for plank 10 feet and shorter, and 18 inches for longer plank.  You can cantilever the plank further, but you have to tie down the other end so it doesn’t flip up.  Also, if you decide you want a diving board on your scaffold, make sure the cantilever can handle the load.  Better yet, use the right size plank if you think there will be a problem with plank abuse.
  3. Plank shall be overlapped at least 12 inches or secured from movement.  This is logical once you think about it; if the minimum overhang for each plank is 6 inches, then the minimum overlap would be 6 inches plus 6 inches, 12 inches,  Please note there is no maximum overlap.
  4. The space between each plank shall be no more than 1 inch.  This is so your stuff stays on the plank and there is no tripping hazard,
  5. The minimum width of the platform, under normal circumstances, is 18 inches.
  6. The maximum distance from the front edge of the platform, not the scaffold but the platform, is 14 inches for all trades except plasterers, where the distance is 18 inches.  If you are using an outrigger scaffold, the distance is 3 inches.  If you aren’t sure what an outrigger scaffold is, look it up in the OSHA standards.  It is NOT the side bracket, commonly called an outrigger, that is used with frame and systems scaffolds.
  7. The maximum distance from the back edge of the platform to the guardrail system is 9-1/2 inches.  If you are using a toeboard for falling object protection, it has to be at the back edge of the platform, not back where the guardrail system is.


Wood plank make good platforms as long as they maintain their integrity and strength.  Therefore, maintenance is crucial to a safe scaffold platform.  If you are using a manufactured plank, such as laminated veneer lumber (lvl), follow the manufacturer’s recommendations.  If you are using a solid sawn product, ask your supplier for advice.  The reputable suppliers will know what needs to be done to keep a plank in good repair.  Also, the Scaffold Industry Association has a pamphlet that includes recommendations for visually inspecting plank for damage.  The pamphlet addresses splits, knots, holes, saw cuts, warp, twist, and other factors that can have an adverse effect on plank.  If you are responsible for inspecting your plank, I strongly recommend obtaining this document from the SIA.  Its’ cost is nominal and the information invaluable.  Plank can also be machine tested to determine the strength of an individual board.  These testing machines are available on a rental or sale basis for your use in determining the quality of your inventory.


In summary, plank made of wood and other materials can be safely constructed and used to support workers and materials.  It is up to the erector to construct the platform so it stays where it’s suppose to; it’s up to the user to use it properly and not abuse it.  Remember, if you don’t know how to construct or modify the platform, don’t modify it.  If you don’t know how much stuff you can put on your platform, find out.  If you don’t find out, and overload that plank you’re standing on, the end result will not be pretty.

Tags: Scaffolding Scaffolding Planks Scaffolding Platforms plank installation plank maintenance plank strength Resources

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