# Deck joist cantilever distance with multiple intermediate supports

Summary: Looking for advice on allowed cantilever length for a multiply-supported joist.

As described in Deck Magazine (which cites the American Wood Council's construction guide) there are limits to how far a deck joist (also beams) can cantilever.

The typical / simple case is shown in the first diagram. The cantilever can't exceed 1/4th of the joist span:

I'm looking for advice on interpreting this rule in the situation where the joist runs of a series of intermediate supports. I've hacked up their diagram to illustrate this:

So in this drawing the the joist is continuous for distance L which could be potentially much longer than what would be feasible in the first diagram. And though this diagram only shows one intermediate support 'B' but you could imagine there being several.

But is the 'L' in the second diagram accurate? (Allowed?)

My assumption here is that one reason for the L/4 rule is to prevent a 'seesaw' effect. So using intermediate supports to increase L would still prevent this. But there could be other considerations I'm not thinking of...

(Note - I'm aware that the local code official will have their own point of view.)

• Holding the main part DOWN is as important as holding it up, when all your friends come over to your birthday party and all stand on the cantilevered portion. (Bigger the cantilever, bigger the uplift.) Mar 3, 2019 at 17:38