Rim Joist – also called band joist or just band, are the joists that make up the outer most boundary of a floor structure. On the sides of the structure that are parallel with the floor joists they are the out side joist(s). On the sides of the structure that are perpendicular to the direction of the joists the rim joist is attached to the ends of the regular joists, closing off the floor structure. Rim joists rest on the sill plate which is attached to the foundation wall of enclosed structures. The rim joists of decks may rest on piers or support posts, or may be bolted to the side of support posts.