Sistering joists for a cantilever requires removing the rim joist and sliding the new joist in beside the existing one.
Sistered sistering floor joists.
Doing so strengthens weak joists and can help straighten sagging joists.
So a 2 foot extension will be 4 feet sistered to the existing joist with appropriate fasteners 3 nails in a w pattern every 12.
How to sister a floor joist.
The section being inserted and sistered should be twice as long as the cantilever.
Framing lumber is the typical.
Properly sistering floor joists is very important and should not be rushed to save time.
If you have sagging cracked or twisted joists which can happen in older houses this project will provide the extra support the floor needs.