Deck Joist and Beam Cantilevers

15 Nov.,2022


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Cantilever (14)

When the ends of floor joists hang out over a beam, or the end of a beam extends out beyond the supporting post below, the structure is said to be cantilevered. Not only do most people prefer cantilevers for aesthetic reasons because the posts are tucked underneath, but they also allow the builder to be less precise when locating the posts during construction. Given the need for tables that tell you how to safely cantilever lumber, you may be surprised to learn that cantilever tables are virtually non-existent.

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. These tables truly cannot be found anywhere else and are yet another reason why BestDeckSite really shines.

One of the concerns that's often voiced in the context of cantilevers is "uplift". This refers to the fact that when only the cantilevered portion of the joist or beam is under load, the opposite end wants to lift up. It's the same reaction that occurs when you sit on a see-saw. The opposite end wants to lift up.

The impact of uplift is an over rated concern. Sure, it's a factor, but in almost all cases, the resistance offered by a standard joist hanger or a small hurricane strap is more than enough to prevent uplift. The only time when it is really a factor is when beams (not floor joists) are pushed to their limit. In those cases, the uplift on the second post in from the cantilevered beam can be substantial and requires special attention.

We guarantee that you'll learn everything you ever wanted to know about cantilevering floor joists and beams on BestDeckSite. There are over a dozen tables to help you readily decide just how far you can cantilever your lumber for any type of situation. Not only do the tables help you size your cantilevers but they'll also tell you when uplift is a concern and even when you're getting into a situation that is best handled only by experienced builders.

For example, let's say we're building a deck out of 2x6 lumber in an area of the country that gets up to 60 pounds per square foot (psf) of snow. (If you're not sure how much snow to design for, check out the snow maps and ask your local Building Inspector.) Since most building codes require designing for drifting snow loads, we'll assume that's a condition for our cantilever example. So the question is, "How much can we cantilever the far ends of the joists?"

Looking at the table below, we see that 2x6 floor joists can be cantilevered up to 2 feet and 6 inches (2'-6") when the joists are spaced 16" apart. The table also indicates that we need to keep the length of the joist that is not cantilevered between 4'-0" and 6'-6". In so doing, we're assured of having a solid deck and that uplift is easily handled by a joist hanger or small metal strap.

Incidentally, you may have noticed that this particular table is specific to decks attached to the house and that don't use a center beam. BestDeckSite floor joist and beam cantilever tables address all the possible combinations related to the number of beams and the location of the beams and cantilevers. All you need to do is click on the picture that represents your deck and read from the table.