The plumber ran a 3-inch drain along the bottom of a 2x10 floor joist and cut a 3-inch-deep notch across the bottom edge right in the middle of a 14-foot span, then screwed a steel strap across the notch.

No, the strap does not restore the joist's strength.

Here's why:

Code Violation: The International Residential Code (IRC) Section R502.8.1 governs notches in wood floor joists. For a 2x10 joist (actual depth ~9.25 inches), the maximum allowable notch depth is 1/3 of the joist depth, which is approximately 3.08 inches. While the 3-inch notch is technically within this limit, the location is critical.

Critical Location: The notch is cut in the middle third of the span (7 feet from either end on a 14-foot span). IRC R502.8.1 explicitly prohibits notches in the middle third of the span because this area experiences the highest tensile stress during loading.

Steel Strap Insufficiency: A steel strap, even if properly installed, cannot adequately restore the tensile strength lost by removing the bottom fibers in the tension zone. The strap would need to be engineered (size, thickness, attachment) to transfer the tensile forces that the wood fibers originally carried. Standard straps are not designed for this purpose.

Correct Solution: The proper fix is to sister a new joist alongside the damaged one, or install a properly sized and engineered steel beam/plate that spans the entire notch area and is anchored to transfer loads effectively.

Conclusion: This installation violates the IRC and compromises the structural integrity of the floor system. A licensed structural engineer or contractor should assess and repair the joist properly.

No. The strap does not restore the joist's structural capacity. This is a critical structural defect.

Code Violation (IRC R502.8 / IBC 2308.8.2):

• Notch Depth Limit: Notches in the bottom edge of a joist are limited to 1/6 the joist depth (1.625" for a 2x10 actual 9.25").
• Notch Location: Notches are prohibited in the middle third of the span (where bending stress is maximum).
• Your Case: A 3" deep notch in the middle of a 14' span violates both limits severely (3" > 1.625" and wrong location).

Why the Strap Fails:

1. Tension Face Destroyed: The bottom 3" is the tension face. Wood fibers in tension cannot be "strapped" back together effectively; the strap bears on crushed wood fibers at the notch corners.
2. Shear Transfer: The strap relies on screws into the remaining 6.25" of joist above the notch. This creates a stress concentration (shear lag) likely to split the wood or pull screws.
3. No Engineering: Straps are for reinforcing existing capacity (e.g., sistering), not creating capacity where the primary tension member is severed. This requires an engineered repair (steel flitch plate, LVL sister, or mid-span bearing wall).

Immediate Action:

1. Stop work. Do not load this floor.
2. Hire a Structural Engineer (PE) immediately to design a repair.
3. Plumber Liability: The plumber created a code violation and structural hazard. Their "fix" is negligent. Document photos for insurance/claims.

Do not accept the strap as a fix. It masks a dangerous condition.