When cantilevers shorter than that are used, the old table would be overly conservative, and the new factor accounts for that.įinally, the treatment of deck board spans was revised. This is meant to address the fact that the deck beam table is derived based on an assumed cantilever length of one-fourth of the joist span. The Effective Deck Joist Span Length is the actual joist span multiplied by a joist span factor that is determined by the ratio of the joist cantilever length divided by the supported joist span. Furthermore, the deck beam span lengths in the table are now based on the Effective Deck Joist Span Length, not the actual joist span. As was also done for other tables, higher snow loads were covered. A related change clarified application of deck beams, limiting the cantilever to one-fourth of the actual beam span, rather than one-fourth of the allowable beam span.Īnother major change revised the table for spans of deck beams. The beam spans are based on both beams being fastened together. The intent is to prohibit the practice of notching both sides of the support post and installing one beam member on each side. One specifies that deck beams made of two pieces of lumber must be fastened together. Deck Guard ConnectionsĪ couple of the changes dealt with installation of deck beams. While not providing exact details, the new Section R507.10, Exterior Guards, will reinforce that guard loads have to “be transferred to the deck framing with a continuous load path to the deck joists.” The new section states that where the guard post is connected to the side of a joist or beam, that joist or beam must be connected to adjacent joists to prevent rotation of the beam, and when the guard post is mounted on top of the decking, it must be “connected to the deck framing or blocking and installed in accordance with approved manufacturer’s instructions to transfer guard loads to the adjacent joists.” Previously, the Deck Code Coalition had attempted to put in actual prescriptive details for mounting of guard posts, but those had been disapproved, so they probably thought that this was the best they could do for now. A new method of analyzing joist cantilevers resulted in a new deck joist span table with the maximum cantilever based on the adjacent joist span rather than the joist spacing.Īnother change provides generic instruction for construction of guards so they can resist adequate lateral load. Revised deck joist span tables, deck beam span tables, and deck ledger connection tables were added that cover 50, 60, and 70 psf snow loads in addition to 40 psf live loads. The deck post height table was revised to make the post height based on tributary area of the post. It revised the footing sizes in Table R507.3.1, allowing some smaller footing sizes for members with lower demand loads. It clarified that decks are designed for either the live load or the ground snow load, whichever is greater. One change made general improvements and expanded the use of the tables throughout the section. For the 2021 IRC, seven of their proposals were ultimately approved, making significant improvements to the deck section. This post will continue with the primary changes to Chapters 5 through 8 of the IRC.įor the 2018 and the 2021 IRC, an informal group known as the Deck Code Coalition had been working to develop detailed prescriptive requirements for the safe construction of decks. In the last post, we described the primary structural and wood-related changes in the 2021 International Residential Code, Chapters 3 and 4.
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