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The original item was published from 1/11/2022 9:42:00 AM to 1/13/2022 1:44:01 PM.

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Planning & Building

Posted on: November 2, 2021

[ARCHIVED] Accessory Dwelling Unit Regulations

Title: City Council Scheduled to Update the Accessory Dwelling Unit (ADU) Regulations and Establish New Regulations for Two-Unit Projects Allowed Under Senate Bill 9 

Summary:  City Council Scheduled to Formally Adopt Updates to the Accessory Dwelling Unit Ordinance and Adopt New Regulations for Two-Unit Projects Permitted Under Senate Bill 9 on November 15, 2021

City Council held first reading at its November 1, 2021 Council meeting to introduce an ordinance to update the City’s Accessory Dwelling Unit (ADU) regulations and an ordinance to establish new regulations for Two-Unit Projects that will be permitted in Single-Family Zoning Districts as of January 1, 2022 (based on new state law established under Senate Bill 9).  Second reading and formal adoption of the two ordinances are scheduled for the November 15, 2021 City Council meeting and will become effective 30 days after adoption.

The ADU Ordinance is modelled based on the City’s existing Urgency ADU Ordinance, plus modifications to the Floor Area exemption; calculation of overall height for an ADU; clarification of rear and side setbacks for through and corner lots; and establishing a definition of breezeway, see details below. 

The Two-Unit Ordinance is based on new state law.  Council also adopted an addendum to the Single-Family Design Guidelines to provide “objective guidelines” at the November 1, 2021 hearing.  Staff also noted that additional ordinances will be forthcoming to further address SB9, including regulations related to urban lot splits, affordability restrictions and demolition restrictions.

For More Information: 

Council meetings are now held in person at 6:30pm in Council Chambers located at 26 Corte Madera, 2nd Floor, Mill Valley, CA. Please provide written comments prior to the meeting to Danielle Staude at; or provide oral comments at the meeting by attending the hearing, see details below.

To watch or view the meeting remotely or download materials: Go to the watch meetings online website and select the date of the hearing (November 1 for 1st reading and November 15, 2021 for 2nd reading and adoption). 

Addition Details about the Ordinances:

ADU Ordinance

    Floor Area Exemption.  The Planning Commission and City Council have heavily debated the long-standing Floor Area exemption, which allows homeowners to deduct square footage from the total allowable square footage on a lot as an incentive to build an ADU.  With new state laws, there are now other incentives that are granted to build an ADU project. As a result, Council recommended removing the Floor Area exemption temporarily until staff provides further research and options that will allow the City to reinstate a local incentive for creating affordable smaller scale ADUs, including ADUs above a garage. 

    Overall ADU Height.  State law now permits a detached 16’ ADU on any given parcel.  Staff has clarified how applicants should measure the overall height of an ADU, which is now defined as “the vertical distance from the lowest exterior wall (measured from finished grade) to the highest point of the Unit”, which may be the ceiling for basement units or roof ridge for Detached ADUs. 

    Rear and side setbacks: Clarification for corner and through lots since State Law allows reduced four foot “rear and side” setbacks for qualifying ADUs and two-unit projects.  

    Breezeway: Defining and clarifying that an ADU connected by breezeway is considered a “Detached ADU” and is therefore subject to height restrictions of 16 feet.  

    Fire Safety:  Both Planning Commission and City Council have expressed interest in further regulating those ADUs proposed in hillsides and high fire severity zones. Planners noted at the City Council and Planning Commission hearings that they are actively collaborating with the City Attorney and  Southern Marin Fire District in order to bring forward a separate ordinance that would adopt local amendments to the Fire Code specifically to address ADUs in these fire prone areas. 

Two-Unit / “Duplex” Ordinance

On September 16, 2021, Governor Newsom signed Senate Bill 9 (SB 9), which requires cities and counties in urbanized areas to ministerially approve up to two residential units (either contained in one structure typically known as a “Duplex” or in separate structures) and “urban lot splits” for parcels located in single family residential zones. Ministerial approval means that the City cannot conduct a public hearing or discretionary review. SB 9 will become effective on January 1, 2022.   House

The new legislation also creates allowances for urban lot splits, which will be addressed in a subsequent update to the subdivision ordinance (MVMC, Title 21).

The following provides a brief summary of key provisions for each type of ministerial approval required by SB 9 that is addressed in the new Draft Ordinance: 

    Number of Units: Up to two new housing units, or the addition of one new unit to an existing unit. The two units may be adjacent or connected. An ADU or JADU may also be added to each unit when combined not combined with an urban lot split. 

    Objective Development Standards: Objective zoning and development standards may be applied, provided the standards do not physically preclude the construction of up to two units of at least 800 square feet each.  

    Rear and Side Setbacks: Up to four feet may be required from the side and rear lot lines, provided that no setback may be applied to existing structures or structures constructed in the same location and to the same dimensions as an existing structure. The City can apply its own front setback, provided that the front setback does not preclude the development of at least two units of at least 800 square feet each.  

    Parking: One off-street parking space may be required for each unit, unless the parcel is located within one-half mile of a high-quality transit corridor or major transit stop or there is a car share vehicle located within one block of the parcel. Bus service in Mill Valley does not qualify under the SB9 definitions and therefore any proposed two-unit project or lot split granted under SB9 regulation will be subject to parking requirements.  

    Short-Term Rentals Prohibited: Local agencies must require that tenancies be longer than 30 days.

Local agencies may deny applications for two-units under the following circumstances:

o    The development is located in (1) the coastal zone; (2) wetlands; (3) very high fire severity zones, except if the proposed development incorporates fire hazard mitigation measures pursuant to existing building standards; (4) earthquake fault zones; (5) special flood hazard areas (100-year flood zones); (6) conservation or sensitive habitat areas; and (7) certain other areas designated in state housing law.

o    The development would require the demolition of (1) an affordable housing unit; (2) a rent controlled unit; (3) a unit that has been rented within the past three years; (4) housing units removed from rental market within the past 15 years under the Ellis Act; (5) more than 25 percent of the existing structure’s walls, unless permitted by the local agency or the site has not been occupied by a tenant in the last three years; or (5) a designated historic site.

o    The building official finds that the development would have a specific, adverse impact on public health and safety or the physical environment that cannot be mitigated. A “specific, adverse impact” means “a significant, quantifiable, direct, and unavoidable impact, based on objective, identified written public health or safety standards, policies, or conditions as they existed on the date the application was deemed complete.” State law specifies that a general plan or zoning inconsistency is not considered a specific, adverse impact. 

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