Deck cantilever spans

Going to inspect this house tomorrow, when I pulled up the picture I noticed the deck was cantilevered out quite a bit. I don’t know the actual spacing and dimensions yet, but I will tomorrow. Does anyone know what the code chart scale might be ? Based on the 2010 code or something close to that.
Thank you in advance.




In general cantilevers are 2/3 in and fastened and 1/3 out but actually 2’ is all that’s allowed without an engineers stamp.
I had one a couple of years ago where the deck was cantileved out 6’ from the home with 2"x8" joists 24" on center. full dimension doug fir and when I did the math it passed? Building department confirmed it.


The minimum span ratio is 2:1. That is for every foot of cantilever the joist should be two foot inside the house. See attached table from the 2012 IRC Code Book.

Cantilevered Joist.png

Randy, Let me make sure I understand the chart (Please Help), going by the chart a 2x10 16" on center w/ 30 psf- maximum span out from the house is 53" ?

Depends on the lumber also.


The IRC is lacking. It is the very bottom (minimum) standard… and with decks, that is just not good enough.

The attached image depicts a cantilevered deck. Joists should be cantilevered no more than one-quarter of the joist length or three times the joist width (nominal depth), whichever is smaller.

Again, you have to check the cantilever against both the joist length and width.

For example: if you are using a 2X12 (which is 11 1/4" wide), you can only cantilever out 33 3/4" regardless of joist length.


Sam - Your read the table correctly. As Paul indicated and mentioned in condition (a) at the bottom of the table the lumber species and grade makes a difference.

Nick - His picture is a little small, but it’s actually a true cantilevered balcony, not a deck with a cantilever overhang

And an FYI… Southern Pine is currently going through a DE-rating, so do not use old span charts on new construction. I believe the revised charts will be effective in 2015.

Randy, you are correct.