Presumably, they have explored the feasibility in terms of zoning. Cities are becoming more open to ADUs because of the crisis in rental availability.

As they are drawn, I prefer A. The kitchen is too small for an island in plan B. However, if you made an L-shaped kitchen in plan B that would allow for a small table. That would give more space for the living room.

Consider who will be living on each level, and where their kitchen is over your home. Where would you want someone's dishwasher running over your head?

And having lived in an up/down 2 unit for many years as landlord pay extra special attention to soundproofing between floors. It sounds as if there will be plenty of opportunity.

I think your idea sounds like a great one. Bedroom addition/ layout on bottom floor looks great. I don’t know if there is a way to modify this, but if you are using the side/ backyard for yourself, the larger bedroom in the ADU has a lot of windows that face that direction. For privacy reasons, is there anyway you could have the main windows for that bedroom be where the closet is and rearrange that bedroom? I know it’s skinnier in that part of the room, but just thought I would throw out the privacy concern.

You are brave (or naive!) to consider a rental above your home.

What are your plans for a tenant that gets a keyboard and plays piano at odd hours? A tenant that gets a treadmill and runs at midnight or 5 am? One that moves in with a child that screams and stomps around at all hours of the day and night? You will hear all of these things and more!

Before adding to the conversation, I want to know if is approved by local zoning and the neighbors.

@chispa - we avoid that with “if you like loud music, loud parties, or loud television you won’t like it here.” As owner occupied you have more leeway in some areas.

@Mark Bischak, Architect I’m guessing the op lives in CA, where Newsom recently signed a bill allowing homeowners to build up to four multifamily units on their properties, or subdivide their lots.

@mainenell, these days you need to be very careful how you screen and realize that it might be close to impossible to get someone evicted easily, specially if the OP is in CA.

Chispa- I’ve been doing this for 35 years. I am well aware of rules and regulations. And of the necessity to carefully screen. I am well versed in fair housing regulations. But the OP should become very familiar with those regulations. Especially if she is in California, but even Massachusetts and New York. Those states have also become quite anti-landlord. I suggest the OP visit the website MrLandlord.com to learn about screening, fair housing, etc well before she has need of the information. (Personally, I would not consider being a landlord in any of the above states.)

Entry to the larger bedroom looks a bit awkward—straight into the corner of the bed. What if the second bedroom was smaller, like a bunk room or office? Might allow the door to move a little and maybe to add some storage in the bathroom

Thank you all for your helpful comments! We have the go-ahead from local planning/permit department, however we have not started engineering yet. Not sure if that will throw a wrench in or not. We are in CA. And regulations around ADUs have relaxed to allow for more housing.

I absolutely hear and value comments about having upstairs tenants. It’s a concern of mine, but something we think we are prepared for in order to preserve our small yard. And our contractor definitely has mentioned sound proofing. My biggest concern is our bedroom since I’m a light sleeper, and the ADU does not sit over the master bedroom at all.

I am used to being a landlord in CA and understand what that comes with. I have prior experience renting rooms in my own home as well as a single family home. Thankfully, in 8 years I had only one “bad apple” and when I gave her notice she left with minimal fuss. For me, it’s been about going with my gut on people, and so far amazing people have surfaced. Many I’ve made lifelong friendships with.

I should have mentioned some of the window and door placements in the drawings have not fully been “thought out” yet. We did ask our architect if the back/side windows in the larger ADU room could be high for privacy, and he said yes.

As for our budget, we have $350k— possibly up to $450k if we do an equity line of credit. We have been waiting for at least a year for costs to come down. But it’s just not happening so we want to just go ahead. We had devastating fires in our area in 2020 that also has bumped up costs and wait time for everything. Our goal is to have kiddo in this house (a few doors down from a good school) by the time he is 5. He’s 2.5 now.

OP - so glad to know you know and are experienced in this landlording thing. I wish you luck in this. As owner occupied I would think about making one the bedrooms larger and shrinking the second to a small office size. Reducing the likelihood of that crying baby a and tantrumming toddler. Also, a shower without a tub would help with this. Not having the apartment over your sleeping rooms is a really good move. We lived in a similar setup for 12 years. But the building was built in 1920 with balloon framing. 2 of the 3 bedrooms were a 1 story 1970-ish addition. But the older part of the building did have some sound issues.

Have you had an engineer look at the house to see if it can support a second story?

Any shared floors and walls with air cavities will transmit sound from upstairs to downstairs, especially if you're not building from the ground up. Think long and hard about how much you'll earn from rent versus the cost - financially and in terms of your quality of life.

I used to live in LA and moved out of CA 18 months ago. For what you want to do, your budget would not have been enough in LA 2 years ago and prices have only risen since then. We did a similar sized project there 12 years ago and spent your higher amount back then.

Have you had a builder as part of the design process? If you haven't, you might be in for a surprise when you go out for bids.

My acoustics-expert boyfriend suggested that you put down the thickest pads and carpet you can upstairs to minimize the impact of footsteps overhead. :)

Again thank you everyone. Your comments are very much appreciated. We have not yet had an engineer look at it. That’s our next step. We have had a builder part of the design and discussion process from the beginning. He’s a good, longtime friend. Good-hearted, very experienced professional and a straight shooter. He has been honest about costs potentially going north of our budget. I think my husband is anxious to move just get started because he knows he, thankfully, has a career in which he can work a lot of overtime opportunities and potentially fill budget gaps if needed.

First, we considered a smaller 1 bedroom ADU mostly just over the garage with just a very small amount (a 2-3 feet) lapping over on top of our living space. But my husband floated the idea of a 2 bedroom and our builder said that building a second story from beam to beam (one side of the house to the other) instead of over just a portion of it would actually save money in not having to beef up the foundation so much. It was a more bang for our buck type of thing. Forgive my lay terms. I’m doing my best to summarize the conversation.

Personally, I am more comfortable with the original smaller 1 bedroom ADU idea. But I think the difference in rental income we could get for a 2 bedroom was what did it for my husband. We are probably naive to move forward without scaling back on the design. This is exactly why I value all this feedback. Thank you.

Kim, I also live in CA. I think you live in a beautiful area with access to redwoods and the ocean.

I'd use the most expensive soundproof drywall and plywood that you can afford. Also, keep the plumbing and drains separate between the Upper ADU. Consider cast iron drains at least on the ADU to avoid hearing their draining water. 

As for the layout, I'd opt for one bedroom that can comfortably accommodate a queen or possibly king bed.  The second bedroom would probably large enough for a twin bed or baby bed.

I typically rent 2+1 units to singles or couple or a single parent with a child. 

The 2+1 units always take longer to rent even if the units are larger (over 1K sq ft).

I'm building a 2+2 detached ADU now in Los Angeles 90049. I started  researching ADUs and building costs at that time. I locked in a contract price fixed contract in September 2021.  I think that you'll have to budget more than  $500/sq ft.  Building costs have only gone up since I was investigating my ADU.