Home Improvement

I have a 4bd/2ba that I want to add another bathroom to. There is a small "office" (it's not big enough to be considered another room) that I would like to convert to said bathroom. The two existing bathrooms are right next to each other in the rear of the house and the water cutoff is in front of the property, on the sidewalk.

What considerations would I need to worry about with a project like that? We don't want to go septic.