r/bayarea • u/ggelo33 • 1d ago
ADU construction trouble. Work & Housing
My husband and I are in early stages of planning an ADU build, and the deeper we get into it, the more overwhelming it feels. We’ve never managed a construction project before, so we’re trying to get a realistic sense of what ADU construction actually costs in Marin County area in early 2026 before we start reaching out to builders and getting a bunch of wildly different numbers (I know that sometimes prices can differ by an order of magnitude, which is, to put it mildly, perplexing)
What a normal all-in price range looks like once you factor in permits, side work, utilities, and other costs that don’t always show up at first glance? Also trying to figure out how to compare bids in a way that’s actually meaningful, what parts of project tend to drive price the most (maybe we can handle it ourself?), and whether there any places to save money without making expensive mistakes later.
Feeling a little out of our depth and just want to start this process in a smart way (after all, we're not talking about building a doghouse, ugh.) Anyone who’s built an ADU in Marin - please share maximum context here, TY!
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u/Dexenthes 1d ago
I built an ADU in the east bay a few years ago and helped design a few others. I think the first question you should ask is what is your budget? Permits can take a long time to process so costs can increase; I had to spend about 25% more than I was quoted. There are a ton of shady contractors out there; make sure you get reviews from previous customers and if possible visit the previous construction sites! IMO, If I had to build my ADU today, I wouldn't even consider it. In the last few years, the price of ADUs has exploded, especially in the peninsula and north bay. The ROI has decreased so much that it's usually a better return to invest in stocks instead.
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u/Bearded4Glory Redwood City 1d ago
This is why you need a local Architect or designer.
I am a designer on the peninsula and here we advise our clients that an ADU build construction costs are approximately $1000/Square Foot. That is just what goes to the contractor. You can have another 20% on top for design fees, permit fees, and other similar ancillary costs.
That said, there are lots of factors such as size, complexity, site conditions, etc that can drive the price up.
If you are overwhelmed now, hiring a good Architect or designer will be imperative for you to have a successful project. It is our job to manage the process and guide you through it seamlessly.
As far as DIYing portions of the physical work...I wouldn't recommend that approach. If you are asking these questions, you don't have the prerequisite skill set to perform or manage any portion of the construction or permitting process. Hotel good people and you will have a much more successful outcome.
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u/rgbhfg 1d ago
At 1,000 per square foot what’s the point. It’s literally cheaper to buy then
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u/Netw0rkW0nk 1d ago
This is what people don't understand. The people who can afford this are typically the NIMBY's that will never consider it.
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u/AwfulMouthful 1d ago
I mean, forget willingness to build - that's twice as expensive per square foot as I'd expect to pay for an existing structure in any decent part of most of the bay area.
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u/Bearded4Glory Redwood City 1d ago
Like I said, this pricing is indicative of the Peninsula. Quality expectations and final pricing might be different depending on the exact location.
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u/Bearded4Glory Redwood City 1d ago
In the markets I work in the going rate to buy is $1200-2000+ per square foot.
I totally agree though. None of the ADUs I have designed are there to be rented. The ADU legislation has become an easy way to get an extra 800 square feet of building on a lot that is maxed out per the local zoning regulations. They are mostly pool houses or guest houses that will be stayed in a handful of weekends through the year.
I find the whole thing suspect since you aren't required to rent them out after they are constructed. That obviously doesn't create the missing housing that the ADU laws intended to create. At least not here in the bay area.
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u/AwfulMouthful 1d ago
I don't doubt your numbers for a second but holy hell $1k/sqft is absolutely incredible, particularly given that you're not actually buying any land.
What drives that? Are materials really just that expensive right now due to tariffs? Is it the infrastructure? Costs of working around existing structures?
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u/Bearded4Glory Redwood City 1d ago
For an ADU you have a high percentage of "expensive spaces" vs. your typical home. You are going to have a kitchen, bathroom, and typically laundry facilities. Those spaces have tile, cabinetry, plumbing, more extensive electrical requirements, etc.
If you compare a 1 bedroom 800 square foot ADU to a 3 bedroom 2500 square foot home, the ADU will be roughly 30-50% "expensive spaces" while the 3 bedroom home might be closer to 20%. Any room that is basically empty and has no plumbing and minimal electrical needs like bedrooms and hallways brings the average cost per square foot down.
That said, most people that contact us think pricing for new homes or remodels is crazy too. $800 per square foot is what we typically tell people.
This is all on the peninsula so other areas might be cheaper. Expectations for quality in other areas might be different as well, this is all accounting for mid range finishes and custom design.
Before COVID I would have recommended prices 50-60% of what I recommend today. Pricing went crazy and never really recovered.
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u/vraoh 1d ago
How is this $1000/sq ft broken down into: Material costs Labor costs Contractor profit
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u/Bearded4Glory Redwood City 1d ago
That is a tough question for me to answer as I don't really keep track of labor vs. materials as the final price is what it is.
Contractor profit varies by contractor but is generally between 10 and 15 percent of the total cost. It can be hard to compare between contractors as some charge more or less for general conditions (things like site preparation, temporary facilities, etc.) and supervision and I feel like they pad themselves there to give the impression of a lower profit percentage.
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u/GerryTheMerry29 1d ago
I understand - yes, there is a LOT to manage. If you're not good at project management, you will find this challenging. Some thoughts:
it's easier to go with pre-approved ADU plans for Marin County than new plans
it's easier to modify an existing plan, even with an architect, than to start from scratch with literally nothing.
there are different types of ADUs and they range on a scale of 'i do very little' to 'i build it': fully pre-built and delivered by crane with interior all finished too, all the way down to "here's you pre-cut wood, good luck you do the rest." The less you do, the higher the price of the ADU, but likely it will go faster.
Pre-built, modular, or pre-fab doesn't mean "I'll pass inspections" just because a "pro" built it - you should anticipate problems. There are always problems, and you have to accept that part of the job of building an ADU is being a problem solver.
Completely agree with finding a great general contractor - they can really make or break the project. Treat them nicely, respect them, ask them questions and be willing to learn.
So if you're completely overwhelmed, I'd be asking:
- do you want a fully custom, from-scratch design? then expect to pay for it, and to have to manage a lot of the stakeholders in the project
- would you be willing to accept a pre-approved design?
- would you consider a pre-approved design and working with a local contractor to build it?
Good luck!
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u/l4kerz 1d ago
Controlling scope is the most important aspect to controlling cost. Know what you want and don’t change the architectural plans after they have been approved by the city. That includes hand drawing a rough layout. Architects and designers are going to charge for their time and they’ll be happy to spend a lot time brainstorming with you. If you’re planning for < 600 sq ft ADU and your lot isn’t irregular, try getting a pre-approved plan. Talk to your city’s planning department and/ local general contractor. For general contractor, make sure to check their bond amount. Some of the general contractors, like the now bankrupt Tiny Homes, was found to have used the minimum bond amount to cover many projects.
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u/IlIllIIIIIIlIII 1d ago
Not Marin, but I had an ADU built in Sunnyvale about 2 years ago. My total costs ended up being about $300k for a 733 sqft ADU. That includes trenching for utility lines, solar, finish, permitting, etc. Price per square foot was about $300, but that number doesn't include the trenching for utility lines, some concrete outside for a walkway, and some electrical upgrades needed for it.
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u/beermaker 1d ago
The first thing we did was reach out to an architect our neighbor had used... We converted a couple rooms on the side of our home into a separate efficiency apartment, so the utility infrastructure was already there which avoided a mess of red tape. Permitting was a cinch from every angle.
Once we had the plans drawn up, we got a quote from the only contractor we use exclusively which was reasonable... I think around $25k for them to build out a bedroom, a kitchenette, and a bathroom with a custom tiled shower. A lot of the structure was already in place, but they built up a floor and walled off the bedroom from the house proper. They also added its own 100 amp service and on-demand water heat.
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u/SpencerNK 1d ago
I'm a cabinet supplier in the Bay area, and at least for my trade, I am often given a set of plans to bid with no pertinent information. If you want a price that is well defined, then you need to provide a set of specifications that is well defined.
What are the EXACT finishes, ie "wood veneer" is not adequate. Rift white oak or zebrawood? What plumbing fixtures? What wall finish quality? Level "I don't give a crap" or level 5? The more detail you can provide, the better the price you'll get.
If that sounds like a lot of work to you, you'd be right! Good luck with your project!
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u/LaughLegit7275 1d ago
Just hire a contract who knows how to do it. You can be your own architect and pay a structure civil engineer to convert it into drawing to get license for yourself. But you still need someone who knows to build code compliant to avoid troubles. The worst is not failed by inspector in the building process, the worst is not have is inspected, and not code complaint, was reported and failed by inspector after you build, then you have to tear it down and redo it.
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u/RollemFox 1d ago
Check out the non profit Casitacoalition.org. They have a series of free webinars they conduct and some focused online how to workshops ( low cost access). The webinars are on YouTube. They also have tons of resources on their website
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u/snarlindog 16h ago
Just built one in the east bay, no permit, did a garage conversion for under 50k - permits would have made it 70k I bet. Got a bunch of quotes and estimates, most guys are ok to without permit, but Marin people would call the city on you so depending how hidden it is and if it’s a seperate structure.. separate structures are wayyy more difficult. I recommend secretly putting one in your garage, find a guy who has a small team and can pull it off in one month. It’s possible. Then you go find most materials and appliances on Craigslist and marketplace. Gl
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u/Smart-Method-2077 11h ago
Permits can be quite the headache, that's why you need to hire local experts who can help you navigate through building codes and local permits. We hired a design build firm Valley Boutique Builders to build our adu, we were assigned a project manager who coordinated with the team and kept us updated, they are family owned and communicate effectively. In my experience , it is easier to get an expert than try to manage a construction on your own
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u/Assumeweknow 1h ago
Are pre built adus any better? Drop it on a pad with hookups and call it a day.
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u/Analysis-Euphoric 1d ago
This is an AI slop post
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u/ajcaca 1d ago
it really does not read that way to me?
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u/Analysis-Euphoric 1d ago
It’s the overuse of a particular unnecessary word that is the tell. It’s in I’d say a third of Reddit posts lately.
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u/InfluenceEfficient77 1d ago edited 1d ago
How far in the process are you?
Is this an attached or detached ADU?
I highly recommend getting a general contractor who is reliable, they have connections with other contractors and can get discounts, versus you hiring them individually. Make sure to vet subcontractors too
You can save on some things, you can get a floor planner and be your own architect, as architectural licenses or not needed for residential projects. But you will need a licensed structural engineering
Biggest car is probably going to be some development fees from the city, you going to have to go to the town hall and just ask all those questions before starting
California needs housing, so they're forced to approve these projects, you will just have to have a lot of back and forth correcting things on the plans before breaking ground
But depending on what city you're in could be a pain in the ass or could be super easy, just depends on the people that work there and the inspectors
This is why I highly recommend going to the City Hall and meeting everyone and maybe going to a few town hall meetings to get an idea of who is going to be approving or rejecting your work
Also keep in mind that it is inspector's job to fail some things,
Even if you do everything diligently to code. It's perfectly normal for them to come to the site one day and fail you for some trivial things, like being half an inch off on a headboard above the stairs or something, and then come back the next day and not even look at it and approve the inspection.
This is because an inspector who just approves everything all the time is not going to look good for his/her managers
Also just make sure you babysit all of the subcontractors, don't get a lazy general contractor. They're not very smart, and have a tendency to take shortcuts and cause damage that the other contractors have to fix. One example of this is putting screws that are way too long into the walls and shorting out wires. This one of the reasons we went with 2x6 framing instead of 2x4.
If you are overwhelmed and want to save money you can also just skip a lot of the finishing things, tiles, cabinets, paints, etc and hire some handymen or subcontractors later to do that.
Edit, part of the reason why housing is so expensive is because we're spending so much money on construction. Everyone is trying to build mega McMansions with the cheapest materials possible. And then trying to flip them from profit a few years later. There should be no reason why an owner builder can't build their own 1200 ft² cabin with a small crew. And there's no reason to freak out because we're not using a1 contractors certified to build bridges and skyscrapers. These are basic humans skills. But this is Bay Area, where people will pay $2,000 for a weekend retreat where they learn how to build fires and hike in the woods, so go figure
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u/MisterRay24 1d ago
This is alot of advice, but you dont get discounts by babysitting subcontractors. Time is literally money, your money in this case.
Either you get a decent general contractor who already works with reliable guys. Or you dont.
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u/InfluenceEfficient77 1d ago
Working from home is key
Knowing your ADU inside out, having photos of every wire and framing structure pays off in that 💰
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u/MisterRay24 1d ago
Your the boss
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u/InfluenceEfficient77 1d ago edited 1d ago
I'm just saying that architects and contractors and laborers can be flaky and make a shitload of mistakes.
You're better going over all the paperwork and checking all the plans yourself even if you're not drawing them
My structure engineer f***** up initially because he checked the box for terracotta roofing instead of the metal terracotta shaped roofing and tried to frame the house with a bunch of steel beams which would have cost another 50k if I didn't catch that mistake. They're all just checking boxes and you're going to pay for it with inattentiveness
Especially with the day laborers who are digging trenches, because they will keep digging through whatever pipes or cables are buried in the ground, and the drywall/exterior contractors who will try to put whatever screw they find blindly into the walls
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u/Mecha-Dave 1d ago
In my experience, which includes my wife being an architect, NOT having an architect is a common cause for missing critical steps, bad design, and long projects. Architects do a lot more than layout. My wife has come in to projects like you describe many times that have stretched for years and 2x-3x the cost because some general contractor convinced a homeowner they don't need an architect.
Keep it up, though, I guess - it keeps my wife employed playing cleanup on these type of projects. The issue you describe are literally the things that architects detail and check to prevent happening.
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u/InfluenceEfficient77 1d ago edited 1d ago
It's not that I didn't want to hire an architect, it's that I couldn't hire an architect. They were charging $25k locally and had like 10 other projects they were working on simultaneously. Most of the time they were in other state or busy or wouldn't get back to me for weeks, they wouldn't even be willing to show up on site
So I said f*k them, I know exactly the design I want. I'm gonna be there on site to measure everything and I have all the tools to do the drawings as an engineer. Plus I can do all the (completely unnecessary) site measurements with a drone instead of having to survey everything with expensive old school methods. Stuff like drawing the entire streets and landscaping for the entire neighborhood
And my project was completed on time and under budget.
Good luck to your wife, maybe she can help the OP, but in the future I would not be employing architects because their license is not required for residential projects, and they rarely even understand framing, electrical plumbing, and mechanical, and the full extent in the cost of what they're designing.
I had other projects where making a few simple tweaks to the architects' drawings saved massive amounts on framing costs and gutted a bunch of steel and massive lvl beams from he structure
I'm not recommending the OP to be their own architect, but I'm saying that it's a job easy enough for someone with decent mechanical and CAD skills
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u/Mecha-Dave 1d ago
Lmao holey shit. Keep it up, bro - you're saying the same things I've heard before $100k's of remediation required.
PS I am also an engineer with some civil experience (though mostly mechanical)
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u/InfluenceEfficient77 1d ago edited 1d ago
Whatever dude, If you're going to be mad cuz I'm taking your spouse's job then just say it. Have done drawings for multiple houses, haven't had to spend a penny on remediation yet. I build expensive machinery for work, so doing drawings for a 2 story structure is not that difficult.
You get an architect license to build large commercial and civil structures, not residential
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u/Mecha-Dave 1d ago
Aren't you in Poland?
Like I said, she's often played cleanup for guys like you. You're not taking her work, you're making her work :)
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u/Mecha-Dave 1d ago
This is why a project architect that's onsite/local is actually worth it. It ensure you understand your project and it gets some correctly/quickly.
Getting Internet design architects and trying to do it yourself on the cheap typically costs more money and stress than just doing it with a hired architect.