We're considering picking up a place in the near future. In my area, everything is pier-and-beam, but this has an ADU on a slab.

The ADU is a 4/1. (It used to be a 3/1 one-story garage apartment from 1945, but the parking bay has been bedroom-ified.) So the whole thing is on a poured slab.

The only bathroom is off one of the bedrooms. And while that wasn't a big deal back in 1945, it's perceived as more of an inconvenience nowadays.

If we're successful in getting it, I'd like to look at taking one of the extra bedrooms and turning it into a bathroom/utility room, to turn it into a 3/2 with laundry hookups. But with the slab in the way, I have no clue how expensive that kind of change will be. It might even be cheaper to build a little addition... but then I'd start getting into permit territory, which I'd prefer to avoid.

If the under-slab sewer drain is near where you want to add more drains, jack-hammer the slab between, make the connection, and pour new concrete.

OR

If the new drains are on an exterior wall, you can run them to the outside & trench them meet the existing sewer line.

Build a raised platform for the bath floor or at least the tub/shower/toilet area. About 6 inches should do it. Set them and hook up.

If you have to jackhammer the slab anyway just do that and don't do the raised platform.

Based on the age - before you make a decision I'd get a camera in to inspect the sewer line that is existing. A 1945 sewer line is nearing the end of life, if not past it, depending on what it was made of. That will give you more of an answer as to how to address.

If you need to replace the sewer line, I'd take the plunge and jackhammer concrete, run new sewer to old bathroom and plumb for new one at the same time. That will be the cleanest solution, and will give you another 50 years of sewer line.

Otherwise, I'd market it as a 3/1, with a family room, den or game room, where the bathroom is off that family room. :) Then, I'd make the change when you are ready to update the sewer line.

I have a slab house that was built in 1953. I was doing a kitchen remodel and we were only going to replace the drain lines above the slab. Luckily we found out before we put in the kitchen and the bathroom, that some of the underground drain pipes had corroded through. As a result, we had to jack hammer up the slab in the kitchen and bath areas (back to back) and replace all of the drain lines below the slab.

We tried the jackhammer route a few ADUs ago, and it was going to take days and days at plumber's rates, it was amazing how tough going it was. (We've jackhammered before, so this was a surprise.) We abandoned that idea and did the elevated bathroom design instead, with a step up so the plumber could do the slope for the waste line properly. Tied in to existing septic outside.

Give the garage conversion a real good lookover to make sure it was done right. Make sure they leveled the floor instead of leaving it sloped for a garage. Also make sure it's properly vented and insulated. Also check for permit on the conversion. Could be a problem for you later.

Ohhhhhhh!

I like that!

You're very smart, Razorback!

Thank you to everyone for all the perspectives--- they've been very helpful. I've definitely got a clearer idea as to what needs to happen, if we end up with it.

I picked up an apartment property with some garages converted to an ADU, on a slab. While pulling the records I found some discrepancy's. Dates of when the permits were pulled, inspected and finalized. Then a span before a Certificate of Occupancy was give.

The escrow company provided me with Title Insurance with copy's of the two Certificates of Occupancy and stated that all units were legal. I purchased the property.

I went to pull all of the City records on the property and had to pay an inspector to accompany me while viewing records. Records are now closed to the public.

I found out that several contractors, architect's and three owners worked on the ADU over a 14 year period. Things were done wrong but when the Final Cert. of Occupancy was issued, a letter was issued that all concerns were taken care of and the the ADU is now a legal unit.

Around 3 months into my ownership the City issued a Violation Order, I have an illegal unit rented out and told my tenants they need not pay me any rent.

The issue was in the past the owners never paid some of the Housing fee's associate with Rent Control on this unit, since it was converted after the rent control time period was over. BUT, I paid those fee's on the unit two days after I purchased it and updated the information in the Housing Department Computer, Rent Stabilization's Computer and in the County Tax Assessor's computer.