Determining Deck Post Height
A laser level is indispensable to obtain this essential deck-framing measurement.
Posts and beams are the substructure elements of the deck that take the diffuse load of the joists, decking, and everything on top of the decking and direct it to the footings in the ground. The difficulty of installing these framing members is that there is nothing to support them. As a result, much of the work of setting posts and beams is bracing them securely during the installation process.
Posts and beams are generally installed from the ground up. While this may sound self-evident because the beams rest on the posts, there are situations, especially on uneven terrain, where it’s easier to install a beam, attached at the ends, and then install the posts that support the beam between the corners. In this section, you’ll learn both methods as well as common bracing strategies and tips for installing hardware.
We used the laser level when installing the ledger, but this tool really earns its place on the job when determining post height. If possible, position the laser so the laser line matches the control line you used to install the ledger. If you can’t do this, establish a new control line. The deck shown here has a common framing scenario, where a girder beam supports the joists from underneath and the post height is to the bottom of that beam.
To determine post height, you need to add two measurements together. First, take the distance from the bottom of the ledger to the control line and subtract the beam height (see images below). Write this first measurement down and use it as the top portion of every post. The second portion is from the center of the post base up to the laser line. It will quickly become apparent why the laser level is so valuable because it is very difficult to accurately and quickly achieve this second measurement for each post base without a laser. For each post base, repeat the process of adding the constant top measurement to the individual post’s second measurement.
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| 1. Measure down from the bottom of the ledger to the control line and subtract the height of the beam. | 2. Place the end of the tape on the post base and measure up to the laser line to get the second measurement. |
Trade Secret
Avoid confusion by writing the post height on the post-base hardware. Writing all the post heights down on a piece of paper—or worse, a scrap of wood—will just lead to frustration when you lose it. Instead keep the post height handy by writing it where you will need it, on the post base.
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