Problem: Inadequate Floor Joist Support
Improper joist bearing.
When the bearing surface is too small or the connectors and fastenings are too weak, the joists can move, resulting in sagging of the floor.
Use ledger strips:
- Floor joists should have a minimum of 1 1/2″ (38 mm) of bearing at each end. When joists butt into the side of a beam, a ledger strip can be nailed onto the beam to provide the necessary bearing surface. Ledger strips are typically 2″ × 2″ (38 × 38 mm) and are fastened to the beam with two 3 1/4″ (82 mm) nails at each joist. Joists that bear on 2″ × 2″ (38 × 38 mm) ledger strips must also be toe-nailed to the beam with four 3 1/2″ (89 mm) nails. If 2″ × 3″ (38 × 64 mm) ledger strips are used, you need not toe-nail the joist as shown in Figure 22a and 22b.
Figure 22a - Bearing Support For Floor Joist - Ledger Strip
Figure 22b - Bearing Support For Floor Joist - Resting On Beam
Install joist hangers.
- Joist hangers are mechanical fasteners that provide the same support as a ledger strip. Joist hangers are fastened to the wood beam as well as to the joist as shown in Figure 22c.