How To Join Floor Joists Together

Nailing two 2x4s together will work to span about three joists unless the sag is under a weight bearing wall.

How to join floor joists together.

Sistering joists is commonly used when adding onto an existing deck or repairing a deck. Common sense tells you that large floor joists can carry more load and spacing joists closer together also increases the load bearing capacity of a floor. The extra two inches of vertical distance when a floor is framed with 2 x 10 joists rather than 2 x 12s can be quite important for example. Doing so strengthens weak joists and can help straighten sagging joists.

But larger is not always better when builders are constructing a home or adding a room addition. The longer the overlap distance the stronger the connection. Sistering joists means beefing them up with additional material. The amount of weight that each floor joist handles is pretty amazing.

Framing lumber is the typical. You should overhang at least a couple of feet on each side of the beam. How to sister a floor joist. When sistering these pieces together it is easy to put just a few nails in the boards and move on.

Set a hydraulic jack and post under the beam and jack up the joists about 1 8 in. Use m8 110mm coach bolts measure down 30mm from the top and bottom of the joists and drill through both the timbers and bolt together space the bolts out 600mm all the way along from one end to the other should be strong enough for a tap dancing elephant. Tack a beam under the sagging joists. In these cases the overlapped joists help tie the framing together by combining the rigid members over a beam.

Here is a pathetic attempt to splice some floor joists under the bathroom. A day until they re level. The long view makes the overlap seem longer but i believe the nearest one is less than a foot with very few nails. Drooping and joist sag can be seen in the photo.