Deck Building – Beams and Joists
Install a Sturdy Understructure for the Outdoor Entertainment Center
Next in importance after deck design is the understructure - posts, beams, joists, and ledger boards. Learn how to build a sturdy one. No need to hire a contractor!
Deck Building – Beams and Joists
This is number 6 in the Deck Design and Building Series. The first focused on deck design fundamentals, the second on deck framing concepts, the third on lumber sizes and spacing, the fourth on post hole layout and the fifth on installing the ledger board, digging the post holes, and setting the posts in concrete. This article's focus is on how to install the beams and joists.
Install the Deck Beams
The beams run across the tops of the posts and parallel to the ledger board. (Of course, this doesn't apply to a detached deck.)
- Nail or screw post caps to the tops of the posts to receive the beams.
- Use a stake and string line to determine where the beam should be located. Use the 3-4-5 squaring method to be sure the string is perpendicular with the end of the ledger board. Recall that the joists will butt into the ledger, but ride on top of the beams.
- Cut the beams to the correct length. On a cantilevered structure, be sure to allow for equal overhang past the ends of the outside posts. For 4” X 4” posts, it will take two 2” X ?” beams nailed or bolted together. (Where “?” represents the height of the beams for this particular deck configuration. See the lumber sizes and spacing article.)
- Begin with the beam furthest from the ledger board. Set the beam in the post caps.
- Then, simply adjust the beam in the post caps until it meets the string.
- Nail the beam into the post caps.
- Install the remaining beams.
- Use 2” X 4” boards to brace the beams to the posts at a 45 degree angle.
Install the Joists
- Determine the length of the joists. Remember, outside joists butt to the end of the ledger (using a galvanized framing anchor), but the inner ones will be hung with joist hangers. Remember to include the length of the cantilever past the end beam and add a couple of inches.
- Install the joist hangers. The distance between joists is determined by the local construction code.
- Install the joists. One end goes in the joist hanger. Use galvanized rafter ties on the tops of the beams.
- Mark the cantilever overhang on the outside joists and strike a chalk line across the tops of the joists.
- Use a square to transfer the marks to the sides of the joists.
- Use a circular saw to cut off the ends of the joists.
- Nail a rim joist across the ends of the joists.
Check the local building code to determine if blocking is required between the joists to keep them from twisting. Install them if so.
This is a good time to install blocking for any posts for railing, if any is in the deck design. The next deck article will focus on planking (deck boards) and some options. Stay tuned!
