Zoning Codes: Multifamily Granny Flats?

Erick Mikiten, AIA, LEED-AP  

Accessory Dwelling Units (ADUs) conjure up images of single-family homeowners with an underused back yard or aging Baby Boomers who want the retirement income of a rental home on their property. But as of January 1, 2020, new State laws require municipalities to be more flexible in allowing ADUs, including game-changing ADUs on multifamily properties. 

Owners of multifamily buildings are always balancing operating costs and revenue. They may have older buildings with costly maintenance or want to build new apartments, but can’t quite get them to pencil out due to high construction costs. Multifamily ADUs (MADUs) can help solve these problems while simultaneously fighting California’s overpriced housing market. 

The process is comparatively quick and easy, circumventing the difficult planning department hoops typical of multifamily projects. I liken it to getting a Community Chest card in Monopoly that gives you another house on properties that already have hotels on them. This is a true game-changer. 

Local agencies scrambled at the end of 2019 to update their local ordinances to conform with the new State laws. A handful of aggressive planning departments already had ordinances that allowed more than the new laws (larger or taller ADUs, for example), but many others were dragged kicking and screaming into this brave new world. 

Cities are still struggling to align their ordinances with State law, so check the current ordinance where you’re working. But here are some of the most impactful multifamily aspects of the new laws: 

Junior ADUs (JADUs):

  • Multiple JADUs can be created within an existing multifamily building. We were working on a rehab of an 8-unit 1940’s apartment building when the new laws were enacted, allowing us to carve two more units out of unused mechanical and storage space.
  • The number of JADUs is limited to 25% of the original number of dwelling units. 
  • JADUs can be carved out of storage rooms, boiler rooms, passageways, attics, basements, or garages (but not existing living space) as long as the new spaces meet building code requirements.

Location and Size:

  • When there’s an existing multifamily building on a lot, up to two detached MADUs are allowed. These can go just four feet from the rear and side property lines, even if the base zoning requires larger setbacks. 
  • MADUs can be up to 850 SF for a studio or one-bedroom units, or 1,000 SF for two-bedroom or larger units. Some cities, like Berkeley, allow MADUs to be 1,200 SF.
  • Any detached ADU is limited to a 16-foot height. This is in response to concerns that two-story buildings four feet from back yard property lines create a privacy problem for neighbors, and that they are more likely to block views on hillside locations. 
  • Lot size or coverage is not a limitation.

Parking and Emergency Access:

  • New MADUs are not required to provide parking as long as any of the following is true: It’s within half a mile of public transit (even just a bus stop). 
    • It’s in a significant historic district. 
    • It’s within a proposed or existing primary residence or accessory structure. 
    • On-street parking permits are required but not offered to the occupant of ADUs. 
    • It’s within a block of a permanent car share vehicle location.
  • Accessible parking space requirements of the California Building Code (CBC) Chapter 11A still apply, so check with your local agency and the CBC.
  • When demolishing or converting a garage, carport, or covered parking structure, replacement parking is not required. The only exception is required accessible parking.
  • Cities have different safety requirements for emergency access, especially for narrow hillside streets and certain fire zones. Such restrictions on any type of ADU are allowed by State law.


  • MADUs “shall be considered ministerially without discretionary review or a hearing” and are to be approved within 60 days of a complete application being submitted. So an agency can’t slow you down with a public hearing or design review process. 
  • When you’re proposing a new multifamily building AND a detached MADU, the reviewing agency can follow their regular process and requirements for the main building, but then has to abide by the 60-day rule for the MADU. So MADUs are definitely faster if you’ve already got a building in place. 
  • For the few cities that already had a MADU ordinance as of July 1, 2018, State law allows imposition of “standards, including, but not limited to, design, development, and historic standards” on MADUs, but not minimum lot size standards. It’s unclear whether these additional requirements allow agencies to take more than 60 days for their review, so bring this up in your first discussions with a Planner.


  • Unfortunately, encouraging better accessible design in MADUs didn’t make it into the new laws. But we architects need to think about the aging of the Baby Boom population and take every opportunity to create level entrances, accessible bathrooms and kitchens, and other amenities that we’ll all need more more of in the upcoming years. Do future residents a favor while also helping your clients to future-proof their MADUs. My mantra: Make your Granny Flats actually work for Granny!

Multifamily ADUs are a new tool that helps us add value to projects and make a dent in the housing crisis. We should take any opportunity to build these small-scale accessible apartments. They will make our neighborhoods more diverse, more affordable, and more interesting.

Now go forth and multiply.

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