"the cast iron will rust eventually."

Not in your lifetime.

It is more labor, and harder labor, to install.

Thanks brickeyee for your comments. The plumber did say he would charge $300 extra for cast iron, and I don't think he wanted the extra hassle as our job is already quite big. Do you find cast iron makes a big difference in sound insulation? Can the same effect be had with spray insulation, or is our best option that cast iron pipe. The location of the pipe fall is not well placed given it travels through dining room wall.

Carol

"Do you find cast iron makes a big difference in sound insulation?"

I have installed cast iron lines in a number of higher end homes to reduce drain noise.

Folks with multi-million dollar homes do not want to hear the upstairs toilet flush in the living room.

It works far better than any sound insulation since you are adding the one thing that stops sound cold, mass.

Thank you very much Brickeyee for your expertise. I will contact the plumber and hopeful he will agree to put in the cast iron. We will also have a drain lin in the wall in between the kitchen and hallway. I think this location will not both me as much as the one going through the dining room as we use the dining room every day.

Carol

We have an older (1928) house where cast iron was standard during construction. The previous renovation had a plastic stack running next to the kitchen, and any time the toilet flushed upstairs you could hear the water rushing down. In renovating the kitchen and bathroom, we insisted on cast iron above grade level (it was less important in the basement) to eliminate any noise. Would never do it any other way.

Thanks geller for your helpful input. I think we are going to try for the cast iron pipes as well.

Carol

The older cast iron is quieter, but even new cast iron is still much better than plastic for noise control.

The mass of the pipe itself limits how much noise can be transferred from the water.