We are remodeling our 5x8 bathroom and extending it into an old mud room on the back of the house. Right now the toilet sits within the 5x8 space, but will be moved directly back into the 40" wide mudroom (about 3-4ft).

I have easy access to all the piping from the basement which is unfinished and the mudroom extends beyond the foundation of the house but sits on its own foundation (more or less like a deck). The floor in the mud room is lower than the subfloor in the bathroom (which is rotted by the way, but the beams are good). So I plan to rip out the old flooring and put new sub floor in to move and set the toilet on.

Flooring:
What special concerns do I need to do for the flooring? I assume standard 5/8 plywood, but do I need to run joists within specific distances of the toilet? Should I frame it first, then do the piping, then lay the subfloor?

Piping:
The house was built in 1907, I have cast iron piping but... It was remodeled and some one has already gone through the trouble to couple 4" PVC into the cast iron. I've read all the other posts on moving toilets so what I am expecting is to literally extend the existing horizontal pipe (which is about 1ft right now) with a longer one making the run 4-5ft long and leaving the existing vent about 3-4ft from the toilet.

Any hidden problems or difficulties you think I may run into? (and yes that is vague but just general issues you usually run into because I don't do this for a living so its all new to me ;) )

Thanks,
Evan

Bump. Somebodies got to have some answers, ideas, comments?

The usual order of things is:

Framing of the walls and floor joists.

Sheeting of the floor.

And then the plumbing goes in.

As for the trap arm (the portion between the vent fitting and the closet flange) you are allowed 5 feet of developed length on a 3" trap arm.

Excellent, Thanks. Put the floor in, then the plumbing, check.

As for materials sheeting the floor, any recommendations? My book says plywood, but the store has different 4x8 sheets ranging from 15 bucks a sheet to 40!

I plan to tile the room so I'll be laying down cement board. If I do that does it give me flexability on what sub floor material I can use?

Another plumbing question. If I put in a double shower head setup, would I want to run a second on/off to the second head on the same side as the 1st shower head or the other side of the tub?

I think OSB has largely replaced plywood as subfloring. If you do go plywood, look for something like CDX. The CD means one side looks bad, and the other worse. The important thing is X for exterior, with water resistandt glue holding it together. Your cement board will cover up irregularities in either OSB or CDX. Screw every thing down good with exterior grade deck screws.