What is the maximum number of load bearing studs in a row that can be notched?
There is no specific limit on the number of sequential studs, as the 7/8&quot; limit is intended to reduce the potential stresses, however, given the choice, I would rather drill than notch:
2308.9.11 Bored holes. A hole not greater in diameter than 40 percent of the stud width is permitted to be bored in any wood stud. [...]
and
In no case shall the edge of the bored hole be nearer than 5/8 inch (15.9 mm) to the edge of the stud.
So 40% of 3.5 in gives you ~1 3/8&quot; to use, often much more than you need for supply lines.
My concern though, is that you're thinking of notching for a waste line, and notching 7/8&quot; to add a 1 1/2 or 2&quot; drain line is... I'll just say that I'm with @JohnSmith in that I wouldn't bother, but then I don't know your specific situation.