Until recently, 4x4 posts were used to support decks with little thought to how much they carried or how tall they were. The 2015 IRC introduced a prescriptive method for sizing deck posts, though it included a maximum post height of 8 feet. Prescriptive design is a cookbook for construction that eliminates the need for a design professional; unfortunately, like a cookbook compared to a chef, it’s going to be limited in what it offers. For example, the maximum heights of 4x4 and 6x6 posts allowed by both the 2015 and 2018 IRC were based on the greatest possible area of deck that could be generated with IRC design tables. This resulted in every deck having an 8-foot height limit for 4x4s based on loads coming from a 2-ply 2x12 beam with 2x12 joists 12 inches on-center and cantilevering past the beam more than 4 feet.

Fortunately, the 2021 edition of the IRC has addressed this problem, and includes a post sizing table that can be used to accurately size deck support posts up to 14 feet high based on the deck design. In this 90-minute Building Code College webinar, Glenn Mathewson discusses the details and the design behind the new 2021 post provisions. CEU credits are available for the webinar, which will be held November 9, 2021, in two sessions:

  • 3:30 pm – 5:00 pm (Eastern time)
  • 6:30 pm – 8:00 pm (Eastern time)

The fee for the webinar is $23.00. To learn more or to sign up, click here.