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There are several factors that determine the maximum joist cantilever overhang for a deck. Learn about deck cantilever and overhang rules at Decks.com.
If you’re maxing out a joist span, figuring out the allowable cantilever is easy—just follow the table over from your chosen joist species and size to the right, and the maximum cantilever (referred to as “overhang” in DCA 6) for each on-center spacing is right there.
Section R507.5 notes that deck joists can cantilever up to 1/4 of the joist span. But you’ll notice when you look at the portion of the span table for joists with cantilevers that the joist span for decks with a cantilever is often less than the span for the same sized joist without cantilevers.
The 2015 edition of the deck joist span table allowed a universal 1:4 ratio for the maximum cantilever and solved the nonlinear problem by providing two different maximum joist spans—one for joists that do not cantilever, and one for joists that do.
In this article, I’ll explain how to navigate the updated deck-joist-span table (R507.6), how joist spans and cantilevers are measured, and how I select joists for a deck design. I’ll also introduce how to interpolate the maximum cantilever when the joist back span falls between two columns on the table.
On BestDeckSite, we've created dozens of floor joist and beam cantilever tables to answer all your questions. All our cantilever tables automatically factor in for lumber type, outdoor "wet service" conditions, code requirements, and any drifting snow load affects.
Deck beam spans shall be in accordance with Table 3 and can extend past the post face up to LB/4 as shown in Figure 3. Joists may bear on the beam and extend past the beam face up to the lesser of LO or L/4 as shown in Figures 1A and 2, or the joists may attach to the side of the beam with joist hangers as shown in Figure 1B.
Joist Cantilevers. According to the new span tables and IRC provisions, cantilevers can extend up to one-fourth the backspan of the joist. This means that joists, such as southern pine 2x10s at 16 inches on-center, spanning 12 feet are allowed to cantilever up to an additional 3 feet (see illustration, below).
Mike Guertin breaks down how to read the new code tables and adjustments for cantilevered joists to more accurately size the beams on a deck.
Table R507.6 identifies the maximum joist spans and cantilevers by load, species, joist size, and spacing for #2-grade lumber. The Code further identifies how blocking at the beam and joist hangers at the ledger board is to be used.
A cantilever is a deck section that projects beyond the supporting joists. You can use this to create a covered porch or extended seating area. The maximum cantilever distance is 4 foot 6 inches, but it’s best to keep it within 2 feet for most decks.
Cantilevers with a live load of up to 40 pounds per square foot (psf) are permitted according to the Building Code (IRC 2009 or IRC 2012); however, your engineer may permit larger cantilevers. If you upgrade to joists that are 2 by 10, the building code will allow you to cantilever for over 5 feet.
The 2021 IRC provides a pre-engineered span table for sizing deck beams, but it offers a lot more design flexibility than may appear. This video is a quick-...
1. Joist stock greater than 4.9 m not typically available. 2. Where guards are required, joists and rim boards shall be a minimum of 38 x 184 mm. 3. See Figure 1 for details in regards to cantilevers. TABLE 2b - DECK JOIST SPANS NOT INCISED (ft-in) Maximum Nominal Allowable
The principle of a cantilever deck is similar to a teeter-totter, where one end is anchored, and the other end is free to float in the air. The magic lies in the framing, which extends back into the structure of the house, using the strength of the joists to keep it from tipping over.
There are three ways to determine deck joist span and spacing – formula, calculator, and joist sizing and span tables. Regardless of the method used, span and spacing depend on the type and grade of the wood, cantilever, beam size, height off the ground, footing size, and live load values.
Thinking about installing a cantilever, girder or drop beam to support your deck joists? Learn why they are important to the supporting your deck frame and how to install them at Decks.com.
Beginning in 2015, deck joists of solid-sawn lumber at common on-center spacings have been allowed to cantilever up to one-fourth their span in most circumstances (for example, joists spanning 12 ft. can cantilever 3 ft. beyond the beam).
Many decks have joists that span from ledger to and over a beam, cantilevering a few feet past the beam. Unless the calculator or table SPECIFICALLY includes input for the cantilever portion, one must assume that it calculates for a simple, single span.
When building a deck with 7-ft. joists, you know the beam can span somewhere between 7-7 and 8-0, but you don’t know exactly where. Check with your local code official, or simply drop back to the shorter value in the table and assume the allowable span is 7-7. Fastening and Cantilevering.
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