If you’re building a deck, you need to support the deck floor. Deck floor support comes from a variety of places, including the footings, the frame and beams, and the deck joists.
Here are some tips and tricks for installing deck joists.
How to Install Deck Joists: Step by Step
Step 1: Measure and Mark 16″ Along the Beam and Frame
Typical deck joists are spaced 16” from center to center. Measure and mark every 16” along the beam and frame or whatever supporting beams you’re using to mount your joists.
Step 2: Install Your Brackets
Grab a scrap piece of pressure-treated lumber in the width/height of your joists.
Slide a bracket onto the scrap lumber so that the end of the bracket is flush with the end of the lumber.
Some brackets will stay parallel on their own, but some will flare outward, so you’ll need to hold them in place as you pound the bracket.
Have a helper squeeze the bracket on the scrap piece of wood, and center it along your marked 16” guideline.
Use the largest size of outdoor nail that will fit into the holes of your brackets. In this case, the joist brackets require #10 size nails, which are quite substantial.
While the helper holds the bracket and scrap wood in place, pound the nails halfway into the top two bracket holes.
Remove the scrap wood so it’s out of the way.
Pound in the top two nails so they are secure and tight against the bracket metal.
Avoid hitting any part of the bracket itself, as your joist needs to fit inside the space. If you accidentally hit and bend the bracket, pound it back into place.
Now pound your galvanized nails into the bottom two holes of your bracket.
Keep working down the line, centering each bracket with the 16” marks.
You should now have two rows of 16” spaced marks facing each other, with brackets installed along each side.
Step 3: How to Work Around Obstacles
It’s a good idea to calculate, from the beginning, where your posts hit along the frame or beam. Do what you can to keep these obstacles in between the 16” spaced brackets.
On occasion, you’ll run into a circumstance where the post can’t be avoided. In this instance, the 16” mark hit about 3/4″ away from the footing. A bracket won’t fit here.
To fix this, we’ll need to level the footing post to be even with the joist tops. Grab your reciprocating saw and a blade that’s long enough to get through the post at an angle.
At the precise level of the top of the beam/frame, use the reciprocating saw to cut off the post top. A 6” blade worked well to get through a 4×4 post.
Cutting through the lumber is a quick process if you have a sharp blade. Which you should, both for efficiency and safety.
While you’ve got your reciprocating saw out, cut off the footing tops at the level of the frame and beam boards.
Step 4: Measure and Cut Your Joists to Size
Before we talk about what to do about the joist next to the footing, let’s hang a standard joist. Measure from the inside (against the beam) of a bracket to its opposite bracket.
Use a miter saw to cut your pressure-treated 2×6 (or whatever size you’re using) at that length.
Step 5: Place Your Joist in Its Bracket
Set one end of your joist into one of the brackets. Don’t set it all the way in until the opposite side has worked its way down into its bracket a little.
Use a hammer to force the joist into its bracket. Be wise about this – sometimes, you have to shave 1/16” before you pound it in.
You want these joists snug, so it is a good sign when the joist fits but is too tight to slide in.
Using your #10 nails, and holding the joist in the bracket (the top of the joist should align precisely with the top of the beam or frame here), pound nails into the joist-holding holes.
Alternate sides when you pound in the nails to keep the joist centered in the bracket. So, for example, you would pound in the top left side, top right side, bottom left side, and bottom right side.
Repeat on the other bracket so that your joist is secured.
Repeat for all the joists down the line, measuring and cutting each joist length individually.
Step 6: Alternate Joist Placement (For Large Decks)
If your deck is large enough to require multiple joist groupings, it’s a good idea to alternate the joist placement. Measure and mark 8” in and 16” thereafter on one section, then 16” in and 16” thereafter on the neighboring section. Look at the potential obstacles to determine which measurement would work best in each section.
Install brackets in the same way on this next section.
How to Fit Joist Brackets Next to a Deck Post
We still need to address the bracket that’s not fitting next to the post. Here’s one solution: measure, cut, and attach a joist to the opposite bracket. Then hold the footing end of the joist level with the top of the beam. Cut off the footing and predrill for a couple of lag screws.
Install washers and lag screws into the predrilled holes. Then install a 90-degree corner bracket between the joist and the beam.
You’ve done it! If your deck is made with a bunch of right angles, like a square or rectangle, installing the joists is a straightforward process.
If your deck has protruding posts, mount some framing at the level of the frame and joists around the post. This is the case for these 6×6 pergola posts coming up through the deck floor. Use lag screws to secure the framing.
Tip: Do this before you install joists in this area, or it will be harder to install the lag screws due to the limited space between joists.
Tip: Use Adjustable Brackets for Curved Edges
Some decks have a curved edge or two, where 90-degree hanging brackets won’t work. There are adjustable brackets available in these instances.
Adjustable brackets have spaces in the corner metal to give the bracket flexibility while maintaining its strength and support capacity.
Use the largest decking nails (#10 in this case) that will fit into the mounting holes of the bracket, and install one bracket per side. Use two pairs of pliers to adjust the angle of the bracket more before nailing it in place.
These brackets will help in odd places on a curved deck edge.
You can see here the adjustable brackets along the curved edge of this deck. Once or twice, we had to drill a portion of the end of the joist to accommodate a wall-mount framing bolt head.
We hope you’ve found this tutorial on how to install deck joists helpful. Always use common sense and caution while building and working with power tools.