The section being inserted and sistered should be twice as long as the cantilever.
Sistered sistering floor joists.
How to sister a floor joist.
Properly sistering floor joists is very important and should not be rushed to save time.
Since this is a repair of a faulty or damaged floor joist it is imperative to do this project correctly and there are a few big mistakes to avoid.
Sistering joists for a cantilever requires removing the rim joist and sliding the new joist in beside the existing one.
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.
Framing lumber is the typical.
Sistering joists means beefing them up with additional material.