We have a 8ft deck. Want to cantilver out 4ft past. Have 2 x 8 existing. If we DOUBLE the 2 x 8 for 12ft total is it strong. With a single its only 2ft out that works. Thanks
You can cantilever up to 40% of the joist span (that would be 38") but not more than 4x the joist width (4x7.5=30"). You need to get deeper joists (2x12s) if you want to cantilever more.
Building a Cantilever depends a lot more on the conection/fastening system than the actuall lumber size. J.
I built a deck last year that is cantilevered on two sides. Used engineered lumber (PSL) to support the overhang. Might be something to consider.