Does the open web floor joist require rim board?

My good colleague, Mike Beauchamp, recently presented for the AIBD (American Institute of Building Design). His presentation was part of their ongoing continuing education webinars. The subject was the Evolution of the Wood Floor Joist. One participant asked if open web floor joists still require rim board. I thought that was an interesting question because once you understand everything rim board does, you adopt it.

An essential part of an engineered wood floor system

Rim board sits on the sill plate and forms a band around the perimeter of an engineered wood floor system, matching the full depth of the joists.  Thanks to its connections to the floor membrane, sill plate, and joists, it transfers vertical and lateral loads. This way, it helps the floor system act as a unit.

Here is a rundown of how to connect the rim board. This is as per the ICC’s Acceptance criteria for rim board products (AC124).

Floor membrane connection

Boundary nailing attaches the floor membrane to the rim board.  This helps transfer in-plane lateral loads from the floor membrane through to the sill plate and into the foundation. Use 8d nails at 6 inches on center.

Joist connection

Connecting the rim board to the joists provides lateral support to the joists and resistance against rotation. For example, in storm or high wind conditions, rimboard will help distribute horizontal loads more evenly to resist shear and transmit shear loads to the sill plate, or along the axis of the joists. To connect the rim board to the joists use 8d nails, one for each flange, and one centered in the end block.   On the adjustable end of the TRIFORCE®, it’s just the two nails for the flanges.

Sill plate connection

Along with the above mention functions, the rim board’s connection to the sill plate helps it carry vertical load, of course. This continuous connection plays an important part in ensuring load transfer between floors of the structure. Nailing (Toe nailing in this case) should be at a 30-degree angle at 6 inches on center.



Recommended rim board materials

There are different types of materials available for the job, such structural rim board, plywood and OSB. We recommend APA rated 1″ structural rim board. it has a smooth consistent nailing surface, a very uniform core and won’t delaminate.

Finally, whatever materials you use, it is essential to have a tight fit for proper load transfer.

So, to the question does open web floor joists require rim board, I would have to answer an enthusiastic “yes”!

To have access to more than 70 3D technical details, download our TRIFORCE® Spec Guide!

Triforce Spec Guide

1 Response

  1. Kathleen

    Thanks for this sensible article. Useful detail suggestions with context.

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