The big question mark is relocating my sink to the opposite wall of my bathroom. I am going to call a plumber but i want to know as much as i can before i get into this. I want to install a double vanity. I assume water and waste line will need to run under the floor to the opposite side of the bathroom, unfortunately this would run into the floor joists. What is the protocol for cutting through or notching the floor joists. they are 8x3 wood joists (assumed from the 1st floor joist). the house is a rowhome built in 1920. Will the plumber know this? Is this even possible? Should i demo first then call a plumber? Would a plumber require a real carpenter? Last and most importantly what would one expect in cost.
I am only going to hire a plumber and electrician and do the demo, carpentry, drywall, tileing myself.
You can drill holes in the existing joists to accommodate the new plumbing. The holes cannot exceed 1/3 the depth of the joist, which is about 2-1/2" on an 8" joist. The holes can't be within 2" of the bottom or 2" of the top of the joist, but can be located anywhere along the length of the joist. The plumber will drill the holes and piece in the PVC drain in the floor. You won't have to do it for him.
Some plumbers are quick to notch wood joists. This can be done, but it substantially weakens the structure. Notching is allowed in the joist, but never in the middle third of the joist's span. Notches can't exceed 1/3 of the joist's depth.
Just go over his plan before he starts to make sure he doesn't do any wood butchering that will compromise the structure or cause you to fail your inspection.
As for costs, that's not what this site is for. Guessing what it would cost you would be a shot in the dark. We're better geared to helping you do these things yourself.