True cost of ADU?
We've rented in Oakland for years and are now looking to buy a home here, with the plan that my parents would live with us in a second unit/ADU. True duplexes seem to be a little out of our price range, so we are looking at various types of set ups - houses with large flat lots but no second structure, houses with partial ADUs (garages converted to studios that could be expanded, etc), houses with large lower levels or extra rooms that could be walled off and a kitchen and bathroom added. We're having trouble figuring out what the true cost of an ADU will be and with such a fast-moving real estate market we can't really get actual estimates on a specific property or anything like that before buying. Whether or not we can afford any given home depends on how much adding the ADU would cost, so I would love to hear others experience on how much it cost for them to add one to their home. I'm particularly interested in garage conversions and also in pre-fab companies like Bay Modular which seems great on paper but wondering if costs can add up and how to avoid that. Contractor recommendations welcome but at this stage I'm really more looking for actual cost examples so I can get a sense. Thank you!
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Our garage conversion, about 600 sf with 400ish to be a studio apt, the rest storage, has been estimated at 200-300k. That's not including the architect and permit fees, on which we've spent a few thousand. The garage has a usable foundation and drainage system, so it would cost more if we needed to build those. (This is in Berkeley, but I'd guess Oakland costs are similar.)
I personally haven’t added an ADU to my own home, but we’ve done many renovations and I’ve worked on several projects adding units to properties in Oakland and Berkeley and am familiar with the budget.
I haven’t used any modular construction, but took a quick look at Bay Modular. The $250/sf cost for the largest unit is about as good as it gets for construction costs. However, this doesn’t appear to include the foundation which can be a significant cost.
Other expenses not accounted for as far as I can tell are a Survey, Geotechnical Report, Permitting Costs, EBMUD water meter and service, PG&E meter and service, sewer lateral, structural engineer for the foundation, etc. The sum of those costs can easily add up to $75-$100k. If you can get away with sharing utilities with the existing unit, you can save quite a bit, but in my experience the local jurisdictions won’t allow it. YMMV
Chopping up an existing house or remodeling a garage area can result in some significant cost savings. But this scenario would rely on everything existing being in good condition and would be very location specific.
I personally would budget at least $250k for a freestanding ADU. Possibly more. Which is why we haven’t built one.
I think this is dependent on the site. New construction or remodel, extent of work, location, grade, access, etc. I was looking for a house earlier this year with plans to live with a sister who is disabled. Not the exact same situation but also a value-oriented home buyer willing to consider a project. What was most helpful was meeting up at the house with a contractor for his opinion. That contractor was a family friend so not his usual business but you might try calling around to see if someone would be willing to meet you at a property for a quick informal bid. This is obviously only for properties you have pre-screened to be of interest. Might be considerate to offer a consult fee.
Another way to do it would be to video your walk-through and send it to the contractor for their opinion. Also your real estate agent should be able to give you a ballpark figure too and that info is useful when comparing properties. Either way I think you will need to get quotes specific to the property. Good luck!
I can't answer your question completely, but can share some lessons learned in our process so far. We purchased our house in El Cerrito, largely because it offered us what we thought would be a reasonably inexpensive garage conversion. Like you, we had to make a decision quickly and with limited information, since the housing market doesn't wait.
1. Just because there's an existing structure, doesn't mean it will be usable. The detached garage on our property is sturdy and in good condition, but after purchasing the house and talking to architects, builders and a structural engineer, it the consensus was that it would likely cost us far more to preserve the existing structure than to tear it down and start from scratch. I don't know if this situation would be different if our structure wasn't unreinforced concrete blocks, but in any case, it has been a bummer to realize.
2. Just because your real estate agent thinks something is possible, or will cost within a certain range, does not mean that it is accurate. Treat it as an opinion and do what you can to verify.
3. The thing that we are benefitting from (albeit not having received a permit from the city yet) is the existing footprint of our garage. If that did not exist - or if it had not been a permitted structure - we would have to build our ADU with 4-foot setbacks. Because of the new ADU laws in El Cerrito, we are able to take advantage of the existing area that is closer to the property line, and therefore makes better use of our yard overall. The limitation to using the existing setback is that you most likely can't take advantage of a pre-fab unit (I don't know that they're always more affordable, but assume they usually are) unless it is smaller than the existing footprint.
So many variables and risks... good luck!!
I have not build an ADU, but I have done major renovations to 2 houses and understand the process pretty well. If you are building from scratch, it starts at about $400-600 per square foot depending on finishes. Building material cost have also increased substantially since covid, I would budget at least $300k for building a permitted ADU.
We'll end up spending about $180k on ours, including permits, contractors, etc. This doesn't include yard redesign, which we'll probably look into later. There's a lot of variation, and a lot depends on preferred fanciness, customization, etc. We went with a company focusing on modular builds. We didn't do anything fancy. I worry that the front house and back house will look really different, and we won't be able to sell one day. But for now, this seemed like the best option for housing older parents. For what it's worth, we built 500 square feet of detached living space, plus some storage (non livable but will be used as a gym)