That member is essentially half the size of the adjacent members (because of the notch), but it’s carrying half the load because it’s between the adjacent members. If you must sister a joist, I’d use a 2x4 and nail (or screw) with 10d nails placed about one inch from the top edge and one inch from the bottom edge and stagger the nails so the wood does not split. Make sure there’s 5 nails each side of notch.

Another way to sister is to attach a length of similar lumber along 1/3 or more of the length of an existing joist or rafter. The sistering piece may even run the full length of the existing joist except where it is supported at the ends. This is frequently done to strengthen a rafter or joist. When partially sistering a joist, remember that the way you fasten the joists together is of utmost importance as the fasteners will carry the load to the original joist. In particular, the fasteners at either end of the sistered joist, provided they are not bearing, will experience the most force and have more fasteners than the center of the sistered joist. How to Sister Joists Some Building Codes require sistering to extend a minimum of 4-feet on either side of the affected area and have ½” bolts in a ‘W’ pattern for a stronger connection. Other Codes identify that the only acceptable way to sister a joist is to double it full-length with both ends of the new joist supported on bearing points.

And finally, if you can do a visual inspection of your floor joists and find that some are rotten in places, or have soft spots due to moisture damage. It is important to repair those joists as they’ve lost some ability to handle a proper load. In those instances, sistering the damaged joist is required. Building Code for Sistering Joists Sistering is a term with a variety of structural purposes where a length of similar dimensional lumber is attached to a joist or rafter for reinforcement or extension. Sistering depends on the purpose and structural requirements, and any code parameters.

My idea was also to have 6x2 beams (not bolted to the existing 8x2 joists) running next to every second existing joist . These new 6x2 beams will be raised to the new height of 2" above exist. joists.When sistering a damaged or weak joist with a piece shorter than full length, the ends of the new board are not supported underneath. Double or triple the nail pattern at the ends to improve shear strength. Lag screws or bolts may be used instead of nails, but in a tighter pattern than a doubled joist.