How to Install Deck Joists

If you’re building a deck, you’re going to need to support the deck floor. The deck floor support comes from a variety of places – first the deck footings (posts), second the deck frame and beams, and third the deck joists. Installing the joists is a highly satisfying part of deck building, because after they’re installed within the deck frame, you can actually begin to visualize your deck in reality. Here are some tips and tricks for installing the deck joists.

Note: The author is an experienced, although not professional, builder. Use the advice set forth in this tutorial at your own risk. Always check building codes in your area before building. Neither the author nor Homedit is responsible for damages as a result of following this tutorial.

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Typically, deck joists will be spaced 16” from center to center. Measure and mark carefully every 16” along the beam and frame, or whatever supporting beams you are using to mount your joists.

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Grab a scrap piece of pressure treated lumber in the width/height of your joists (which should be pressure treated lumber).

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Slide a bracket onto the scrap lumber so that the end of the bracket is flush with the end of lumber.

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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 in place.

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Have a helper squeeze the bracket on the scrap piece of wood, and center it along your marked 16” guideline.

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Use the largest size of outdoor nail that will fit easily into the holes of your brackets. In this case, the joist brackets require #10 size nails, which are quite substantial.

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While the helper holds the bracket and scrap wood in place, use those nails to pound nails halfway into the top two bracket holes.

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Remove the scrap wood so it (and your helper’s fingers) are out of the way.

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Pound in the top two nails completely so they are secure and tight against the bracket metal.

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Take care to avoid hitting any part of the bracket itself, as your joist needs to fit inside the space. However, if you accidentally hit and bend the bracket, simply pound it back into place.

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Pound your galvanized nails into the bottom two holes of your bracket now.

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Keep working on down the line, taking care to center each bracket with the 16” marks.

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You should now have two rows of 16” spaced marks, facing each other, with brackets installed along each side.

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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.

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Occasionally, though, you will 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.

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In this instance, we’ll first need to level the footing post to be even with the joist tops. Grab your reciprocating saw with a blade that’s long enough to get through the post at an angle.

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At the precise level of the top of the beam/frame, use the reciprocating saw to lop off the post top. A 6” blade worked well to get through a 4×4 post.

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This is a quick process if you have a sharp blade. Which you should, both for efficiency and safety.

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While you’ve got your reciprocating saw out, you may as well lop off all the footing tops at the level of the top of the frame and beam boards.

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Before we talk about what to do about the joist next to the footing, let’s talk about how to hang a standard joist. Measure from the inside (against the beam) of a bracket to its oppositely spaced bracket.

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Use a miter saw to cut your pressure treated 2×6 (or whatever size you need to code) at that length.

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Set one end of your joist into one of the brackets, but it’s best if you don’t set it all the way in until the opposite side has worked its way down into its bracket a little.

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You can use a hammer to force the joist fully into its bracket. Be wise about this; sometimes you might have to shave 1/16” before you pound it in.

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You want these joists snug, so it is a good sign when the joist fits but is too tight to just slide in.

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Using your #10 nails, and holding the joist firmly down 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.

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Alternate sides when you pound in the nails to keep the joist centered in the bracket. So, for example, you would pound in top left side, top right side, bottom left side, bottom right side.

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Repeat on the other bracket so that your joist is now firmly secured into the bracket, which is in turn firmly secured onto the deck beam and/or frame.

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Repeat for all the joists down the line, measuring and cutting each joist length individually.

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If your deck is large enough to require multiple joist groupings, it’s a good idea to alternate the joist (and, consequently, bracket) 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 in each section to determine which measurement would work best in each section.

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Install brackets in the same way on this next section.

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Remember how we still needed to address the case of the bracket’s not fitting next to the post? Here’s one solution: measure, cut, and attach a joist into the opposite bracket. Then hold the footing end of the joist level with the top of the beam and cut-off footing and predrill for a couple of lag screws.

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Install washers and lag screws into the predrilled holes. Then install a 90-degree corner bracket between the joist and the beam.

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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 pretty easy and straightforward process.

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If your deck has protruding posts, you’re going to want to 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 bits. Tip: Do this before you install your joists in this area, or it will be harder to use your tools to install the lag screws due to limited space between joists.

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Some decks have a curved edge or two, where 90-degree hanging brackets won’t work. There are adjustable brackets available in these instances.

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Adjustable brackets have spaces in the corner metal to give the bracket a bit of flexibility while maintaining their strength and support capacity.

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Use the largest decking nails (#10 in this case as well) that will fit easily 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 easily before nailing them in place.

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These brackets will help in odd places that are bound to arise on a curved deck edge.

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You can see here the adjustable brackets along the curved edge of this deck. Once or twice, a portion of the end of the joist had to be drilled out in order to accommodate a wall-mount framing bolt head.

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We hope you’ve found this tutorial for how to install deck joists helpful. Always use common sense and caution while building and working with power tools. Enjoy this step of the deck-building process!