Problem: Inadequate Floor Joist Support
Cause:
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.
Solutions:
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.
