The deck was 16x10 and we turned it into a 16x20. Two things we did on top of the standard procedures one thinks need to be done.
1. We removed the existing 2x10 band and installed a new longer 2x10 - this literally connected the original framing to the new framing.
2. The original deck had a closed in section with a wall that did not have a supporting post underneath it. We installed two 2x8 joist right underneath the wall.
The rest was standard with the exception of the deck boards being installed at 45 degree angels.
And of course, the one small step that runs along the large deck.