Doing so strengthens weak joists and can help straighten sagging joists.
Sistered sistering floor joists.
Sistering joists for a cantilever requires removing the rim joist and sliding the new joist in beside the existing one.
Sistering joists means beefing them up with additional material.
This article provides step by step instructions and pictures on how to make structural repairs by sistering floor joists alongside weak joists.
The section being inserted and sistered should be twice as long as the cantilever.
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.
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.