Rimboard fills the space between the sill plate and the bottom wall plate, or between the top plate and bottom plate in multi-floor construction. In addition to filling the void, rimboard is an integral structural component that transfers both lateral and vertical forces.

Wood structural panel floor sheathing spans across multiple floor framing members for extra strength and stiffness.
I-joists and the rimboard commonly bear directly on a sill plate that is fastened to the foundation.
I-joists are connected at the exterior wall by a rimboard. The rim joist prevents the I-joists from rotating and helps to transfer load from the wall above to the foundation.