Sizing provisions for posts are included, appropriately limiting their length based on their size. Similar to joists, beams are allowed to cantilever beyond the end post by up to 1/4 the adjacent span of the beam. When there is no joist cantilever, the maximum beam spans are very conservative. The table is based on joist span, as that reflects the load the beam carries however, it is also based on the joists cantilevering their maximum allowable distance beyond the beam. Creating a pre-engineered beam span table is no easy feat, and many design assumptions have to be made. It includes 2-ply and 3-ply beams and heavy timber Douglas fir beams. Most helpful to the industry, a beam span table is now included, and it’s also based on all the proper conditions and design properties. Many builders may find spans reduced from what they are accustomed to however, the maximum allowable cantilever for deck joists is also clearly defined, and the limit of 1/4 the joist backspan is a generous design option. The new table also reflects the design value changes to Southern pine published in 2012. The 2015 code adds a new joist span table that accounts for these conditions and includes new species and sizes, such as redwood and cedar. The joist span tables that have long been in the IRC are not based on a wet-use environment or for incised, treated lumber, both conditions that reduce the maximum allowable spans. However, a second “permitted” lateral load anchor detail has been included. The still ambiguous lateral load provisions for decks have not been completely put to rest, and the notorious anchor detail remains. The 2009 IRC saw deck ledgers addressed, the 2012 set up a section in the IRC specific for decks, and the 2015 brings joist and beam span tables, as well as post sizing and foundation provisions. Largely based on prescriptive tables from the American Wood Council’s DCA6 document, many of the new code provisions may look familiar. We asked Glenn Mathewson, a municipal building inspector and deck construction expert based in Colorado, to provide an overview of some of the biggest changes: The 2015 edition of the International Residential Code brings the biggest update of deck codes the IRC has ever seen.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |