How To Sister Floor Joists Together

Pairing two boards together along their full length where they are supported at both ends is another way to sister joists or rafters.

How to sister floor joists together.

If the new sister bears on wood at least 1 5 on each end then you re good to go. The most common mistakes in this method would be not nailing the sisters together good enough inadequate bearing on one side or another the truss companies use a gang nail to splice wood together pictured at left. Sistering code question it depends on why you re adding them. Set a hydraulic jack and post under the beam and jack up the joists about 1 8 in.

Sistering joists is commonly used when adding onto an existing deck or repairing a deck. A day until they re level. The longer the overlap distance the stronger the connection. Doing so strengthens weak joists and can help straighten sagging joists.

Adding a second joist along the full length of another is also known as doubling up or a double joist. Then set new joists same height as existing ones alongside the old. Tack a beam under the sagging joists. When sistering these pieces together it is easy to put just a few nails in the boards and move on.

If it is a gravity load problem sagging then no nailing is necessary. Framing lumber is the typical. Nailing two 2x4s together will work to span about three joists unless the sag is under a weight bearing wall. The amount of weight that each floor joist handles is pretty amazing.

Sistering joists means beefing them up with additional material. In these cases the overlapped joists help tie the framing together by combining the rigid members over a beam. It is important to jack this end level to keep the floor from sagging any more and to keep the joists from splintering later. If the old joists are truly failing damaged improperly installed you need to nail them together to preserve the lateral load transfer through the diaphragm subfloor.