Framing lumber is the typical.
Sistered sistering floor joists.
Sistering joists for a cantilever requires removing the rim joist and sliding the new joist in beside the existing one.
The section being inserted and sistered should be twice as long as the cantilever.
If you have sagging cracked or twisted joists which can happen in older houses this project will provide the extra support the floor needs.
How to sister a floor joist.
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.
Doing so strengthens weak joists and can help straighten sagging joists.
This article provides step by step instructions and pictures on how to make structural repairs by sistering floor joists alongside weak joists.