I have a two storey house and we are planning on adding a third storey with a very limited budget. I have been working on floor plans based on the assumption it is far cheaper and more straightforward to put the new third floor bathroom directly above the existing second floor bathroom. The primary reason being to simply extend the existing stack to serve the new bathroom.
I have recently read some issues with this plan which lead me to believe I need an entirely new stack to serve the third floor bathroom. The current 3" stack serves a two bowl sink and dishwasher combo utilizing a 1 1/2" drain on the first floor. It then serves a sink, toilet, and bathtub on the second floor. I had hoped to just extend the 3" stack up through the wall in the new third floor bathroom and tie a new toilet, sink, and shower stall into this before extending through the roof.
So is this feasible or can I now have free range on my third floor plans because I will need to add a brand new stack all the way from the roof , through the new bathroom, and tie it into the main drain at basement level?
Any opinions and advice are appreciated.
Thanks very much.