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  • Lorianna Kastrop

ADU Projects: A Step-By-Step Process

By Lorianna Kastrop, Vice President/CFO, The Kastrop Group, Inc. Architects

There is a housing shortage in the Bay Area and a lot of communities are encouraging the construction of Accessory Dwelling Units (ADU’s) in residential neighborhoods. These units are usually a backyard cottage, second-floor unit over a garage, or a garage conversion. They are built to maintain separation or privacy for the primary unit, having their own entry, kitchen, bathroom, and other necessary living facilities. In California there is now more flexibility on the former requirement to provide off-street parking for the secondary unit, depending on your jurisdiction.

If you are interested in building an ADU on your property, here are some basic steps you will need to follow, as well as some links to more detailed information:

  1. Create a wish list. References:



  4. It is likely that you will need to hire a professional site surveyor to show proof of your property line locations. Reference:

  5. Verify your jurisdiction. Do you live within the City or Town limits, or are you in an unincorporated area of the County? Usually you can do this on your City’s website. Then call your jurisdiction’s Planning Department to find out whether a Planning Review (often called an Architectural Permit, or Design Review) is required before you can get a Building Permit.

  6. Hire an architect. Your architect will help guide you through the remaining steps and give you trustworthy referrals to other consultants and General Contractors. References:

  7. for Bay Area projects




  11. Develop a design with your architect. References:



  14. Work with your architect and a prospective General Contractor (GC) to acquire a Preliminary Construction Estimate, to ensure your project is within your planned budget with a comfortable contingency. References:



  17. Be prepared that other consultants will likely be required to complete the plans, depending on the site and scope of the project (e.g., surveyor, structural engineer, mechanical/electrical/plumbing engineer, a Title 24 energy consultant, sometimes also a geotechnical/soils engineer, arborist, and less often a civil engineer). Reference:

  18. Submit for a Building Permit to your jurisdiction. Fees will be due to your jurisdiction for plan review. Your jurisdiction may require other fees at this time.

  19. There will be a waiting period of 6 to 8 weeks (typically) while the drawings are under review for a permit. Make use of this time by obtaining official construction bids from two to four GC’s, now that you have a review set of drawings. References:



  22. Expect plan check comments from your jurisdiction, with hopefully minor revisions requested by the jurisdiction plan checker. Plan checking is often outsourced to a third-party plan checker, as building codes become increasingly complex in California. There could be another 4 to 6 weeks for review time once resubmitted. Use this time to check with your insurance agent that your homeowner’s insurance coverage is adequate while you are under construction.

  23. When you receive notice that your permit is approved your chosen GC will be able to complete standard City forms and “pull”, or activate, the permit to get work started. Reference:

  24. Construction time varies, but expect at least 6 months, even for a “simple” project. Some of this is due to the trenching for installation of utilities to the new building. If it is an addition to an existing building, it may go somewhat faster. Larger units on sites that have complicated terrain could exceed one year. Reference:

  25. If you are building near a property line, you may be required to have the property staked by a surveyor before construction occurs.

  26. Site visits by the structural engineer and architect should occur before inspections by building inspectors. The GC should call the architect directly for any clarifications or questions while the project is under construction. This will help the process go more smoothly.

  27. A last “punch list” visit by your architect to determine if the project is complete as designed. The architect may note some items for the GC to finish or adjust. Then the project will be finalized and closed out. The Building Inspector should sign-off and finalize the permit. Be sure that your GC has paid all the subcontractors so that there are no remaining liens on your property.

  28. Inform your insurance company that you have made a major improvement to your property and revise your homeowner’s policy. Reference:

  29. Plan for increased property taxes (pro-rated based on your current rate). Reference:

Photo of a recent ADU project we completed in Redwood City, CA.

We hope that this checklist, along with the extra references, will give you confidence to move forward with your Accessory Dwelling Unit. You may be planning to move to a backyard cottage so that other family members can occupy the main residence (granny/grandpa unit). You may be creating another source of income for yourself. You may wish to do your part to alleviate the housing shortage. Perhaps you are going to achieve all three of these goals! Contact us if you want help with your project in the Bay Area.

Thanks for reading and as always, we are Designing for Your Reality.

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