Now, here is an example where sistering was for reinforcement.
See that stud to the right of the cast iron main stack, how it is not vertical, and how it is barely under the floor joist above it?
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The cast iron bathtub is right above it!
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We figure, when the house was built (1917) that, after the framing was competed, the plumbers came in and said,"We got to put some pipes here." and grabbed the nearest sledge hammer to make room for it!
You will see that the contractor has two sistered pieces, on either side of that joist. The one to the right is a 2x8 to shore up the floor joist on top of the angled stud (the 2x4 to the left is for leveling the ceiling).
While we had the walls and ceiling opened up we replaced that mess of original plumbing to correct a few issues.
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It looks like you did it right. I see how it was sistered. Floor beams can be a problem when plumbers come in and notch out sections to run pipes. It weakens the structure. In these cases, glue and screwing when sistering can help.
Renovation is about compromise with your budget. Uneven floors are not uncommon, not a big deal unless you play marbles. I’ve seen floors jacked up from below, new beams, all very expensive. Sometimes the floor level of one room is higher or lower by a small enough amount to get on your nerves. Plywood sheathing on the floor can fix that.
You start off with what looks like a simple issue. The deeper you dig, the more expensive the solution.

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