Step 1: get started with your ADU

We have recently interviewed a homeowner, who is about to start her fifth construction project in the Bay Area. It took her close to a year to get ready for permit application for her 5th house! Of course, ADU home is smaller than a typical main house, but it has all the detail of a standard building, thus a lot of details to think about.

It takes time to make decisions. But the more restrictions you have, the easier it becomes.

Check Feasibility

Why are you considering the ADU? This is the most important step in the construction process. As soon as you find that personal reason, the process becomes less stressful and more successful. Promise. And it is the same for any construction project. You can read more about it if you want.

There is a reason that goes back centuries why the architects start with programming (what rooms, what size), then move to conceptual design and only then to detailed design and drawings (visualization). ADU homes are no different.

Looking for a shortcut? Interested in some guided selection that will give you 3 vetted names for Bay Area builders that actually had built ADUs?

Any experienced builder will charge you for the feasibility report – and the costs range from $1000 to $4500 – because it takes time and knowledge. Feasibility report includes the analysis of your city regulations, site analysis, and in our case – several options to build – often with different construction methods.

By going with feasibility report through a single builder – you lock yourself into the construction methods and vendors that this builder knows. What if there are other options that will work better for your site and situation?

Sometimes an ADU is not an option, then we encourage you to consider an addition – might work better for you and your property. We have developed a whole Trello Board for those of you who need help thinking this decision through.

If ADU home is a better solution for your family, we work with seven vetted construction crews that cover a multitude of construction methods, and we can get you to permit faster.

We encourage you to determine your budget at the start of your project – before you start calling the builders. In September 2020, you could definitely build a 500-550 sf ADU with the most modern design you have ever seen for $200,000, event if it sits on a slope. This is close to $400 per square foot with a fixed contract that covers everything. Fast forward to June 2021 – the $200,000 will cover a 430 sf modular unit on a flat lot. Lumber prices are up three times, and they impact all builders – custom and modular.

We have seen anything from $250 per square foot for garage conversions to $1000 ( in fact, the sky is the limit) for detached ADUs built as guest houses. Just remember that the smaller the ADU, the higher the cost per square foot. If you need some help wrapping your head around current prices, this is the best article we have seen on the subject of home-building costs with great illustrations.

Please check the costs for San Mateo county here.

You can also use the calculator by LoanDepot to determine how much an ADU might cost in your county.

If anyone is quoting you a much lower number, check their license, references, and ask if the costs below are included:

  • engineering drawings, architect and/or designer fees
  • city fees for building permits and inspections
  • connection to utilities (fees and trenching)
  • foundation
  • building materials and labor
  • finishes (wall tile, paint, flooring)
  • transportation costs and crane rental if modular
  • site setup (i.e. fence, temporary toilet for the crew)
  • water heater, HVAC
  • solar panels (required for new construction since January 2020)
  • appliances (stove, washer, dishwasher)
  • kitchen cabinets, storage units
  • landscaping
  • construction waste disposal

You will have to add some furniture for your ADU home plus some light fixtures on top of the above.

Something to consider when dealing with costs per square foot:

The smaller the ADU, the bigger the cost per square foot. Main culprit? Fixed costs spread over a smaller number of living space. Here is an example:

Here it is when explained by Kamal Hyder, general contractor and owner of SFBay ADU:

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