Help with incorrect placement of hole in a floor joist – GreenBuildingAdvisor

I have a 50-year-old house and had planned to install a two-piece bath. However, the arewhere the installation was to take place required joist repair. The joists had to be sistered with 2x10s across the full width, which went smoothly, including creating a boxed area for the plumbing and drain.

I knew the stack would likely need to be drilled through one of the nearby joists to bring it up through the wall. However, the plumber seemed to drill the initial 2 3/4″ hole too high, placing the top of the hole within 3/4″ of the top of the joist. Later, he realized the hole was too high and expanded the notch below it.

Now, I’m wondering if the joist can be resupported using 3/4″ plywood gussets on either side of the notched space . The over-notching occurred on the sistered joists (one of which is an extra 1/2″ wider and taller, as it’s the original joist).

If that’s possible, would it be acceptable to fasten the gussets 6 1/2″ from the bottom of the joist (due to water lines in the way) for a span of 8″? I would create a “U”-shaped notch to accommodate the stack pipe (7″ if it fits in the crawl space access). Currently, the gusset’s full height on the inner side of the drain box frame would be 14.5″ long. This seems slightly undersized, so I’m considering adding a concrete block with an adjustable jack on top for additional support.