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Band/Rim Joists (3)

Rim joists, or what are also called "band" joists, run around the perimeter of the deck. In the case where they run parallel to the other floor joists, like the one you clicked on in the diagram, there's nothing special about them. However, rim joists placed at the ends of the floor joists at the far edge of the deck frequently rest on posts and carry the weight of the deck on that end. The floor joists "dead end" into the side of the rim joists and are attached with joist hangers.

On occasion, as in the 3-D diagram above, even though the floor joists dead end into the rim joists, the rim joists don't end up carrying any weight. This can only happen when there is a supporting beam below. Otherwise, the rim joists themselves act as a beam and must be sized accordingly.

To be more concise, when rim joists rest on posts at the far end of the deck, they carry the weight of the deck on that end and need to be sized just like any other beam. This is a three step process that's outlined in brief on the click-n-learn beam page and covered in depth on the beam sizing page. Rather than reiterate that same material here, let's instead look at an important construction detail for weight carrying rim joists.

When the floor joists rest on top of a beam it isn't nearly as important to do a good job nailing up the individual boards that make up the beam. If one of the individual boards stands a little taller than the others, the weight from the floor joists resting on top will just push it down until it is flush with the other beam boards. At that point, the load from the floor joists will be evenly distributed over all of individual boards that make up the beam.

On the other hand, when floor joists are attached to the side of any beam using hangers (this includes load bearing rim joists), it's important to nail together well the individual boards that make up the beam. The idea is to get the separate boards of the beam to work together as a single unit. For example, on a smaller beam made up of only two 2x boards, use three 12d nails every 12 inches driven in at a slight angle. Make sure to get one near the top edge (within one inch or so) and one near the bottom edge as these nails do most of the work.

When the floor joists are attached to the side of a built-up beam, all the load is transferred on the beam through the joist hangers. Since the joist hangers are only attached to one board, all the load is initially applied to that single board via the hangers. If the joist hanger board isn't properly nailed to the other boards that make up the beam, it will end up being pulled down and away from the other boards. The beam will separate and fail.

This is just one of many, many great construction tips and building details that you'll find on BestDeckSite. In addition, there are dozens of tables specifically designed for deck and gazebo building. To learn more about obtaining a password, please see the Get A Password page.