Two seperate but related issues.
I'm in the middle of a kitchen remodel. I'm doing most of the work myself but am having the cabinets installed by a contractor (with sales tax savings it was too cheap to pass up).
Some background: The house is a "2-flat" in Cook County, IL, meaning there are two apartments top and bottom. We are in the process of converting to a single-family home, meaning the upstairs kitchen will be removed after the downstairs kitchen is remodelled.
I have demo'd the downstair kitchen, and am in the process of securing permits for the cabinet install and necessary electrical work. When I talked to the building department about what they needed, they asked if I was adding a dishwasher, and since I am, she said they need isometric drawings, I presume of the DWV system. But I don't quite understand WHY they need them so i'm leery that I am opening myself up to some expensive plumbing work if the inspectors see something they don't like. Why would they want isometric drawing because i'm putting in a dishwasher??
The existing pipe/vent layout looks good to me (see photo below). This is a secondary stack on the exterior wall that drains both kitchens. The drain line is 2" and the vent line, on the right, is 1.5". In the basement, there is a cleanout on the 2" line and the 1.5" vent ties into the 2" drain just above the floor of the basement (along with a drain for a washer and laundry sink) and then the 2" line goes into the concrete, presumably over to the main stack and out to the catch basin and sewer system.
Obviously, I can't see how the vent and drain are tied together above this point because it's in the wall, but are there any obvious deficiencies here?
The second issue is that before I install the cabinets I want to replace the galvanized line with PVC. As you can see in the photo, there are unions on the 2" lines above the 1.5" branch drain, so my intention is to replace everything below those unions with PVC, down to the cleanout fitting in the basement. I may need to replace more than that in the future, but at the moment I want to make sure I take care of what is behind my new cabinets.
My plan is to basically copy what is there other than I may lower the 1.5" line to make things easier for plumbing under a deep sink. I will probably NOT pull a permit for this PVC swap because I don't need to do so for 'repairs under $500". But I still want it to be right, and with the inspectors poking around anyhow I might get called on any errors.
Note that the upstairs kitchen will be removed in the near future so the remaining galvanized pipe above this point will all be vent only.
Thanks for any comments and advice!