ADU FAQs

Accessory Dwelling Units (ADUs) and Junior Accessory Dwelling Units (JADUs) are independent and semi-independent dwelling units with complete or partial provisions for sleeping, cooking, and sanitation. ADUs and JADUs are allowed on properties with existing or proposed single-family dwellings. ADUs are also permitted on lots that are developed with an existing duplex or multi-family units, however JADUs are only allowed as part of a single-family dwelling. The City of Rocklin’s ADU Ordinance (Rocklin Municipal Code Chapter 17.67) was amended in accordance with the State of California law and became effective March 20, 2020. This resource provides guidance on frequently asked questions about Rocklin’s local ADU Ordinance. The California Department of Housing and Community Development’s ADU Handbook can be found here. 

ADU 101

What is an ADU? 

An ADU is a secondary unit with complete independent living facilities. An ADU may be created through the following methods: 

• Building a new detached accessory building
• Converting an existing legal accessory building or structure
• Converting an existing legal accessory building or structure and adding an addition
• Building an addition attached to a single-family dwelling unit. An ADU cannot be created by addition to a duplex or multifamily dwelling structure
• Converting space in a single-family dwelling
• Converting non-habitable portions in a multifamily dwelling structure
• Junior ADU: Similar to a conversion ADU in that it is created from existing space within a single-family dwelling, but meets specific requirements and specifications for a Junior ADU prescribed by State law.

Where are ADUs allowed? 

ADUs are permitted on lots that are zoned to allow residential uses and where there is an existing or proposed residential use. 

Can I build an ADU on a lot with a duplex or an apartment building? 

Yes, the City’s ADU Ordinance allows ADUs on lots with duplexes and apartment buildings. In this FAQ and the ADU ordinance, we refer to these housing types as “multifamily buildings”.

Development Standards

How many ADUs are allowed on a lot? 

• Lots with a Single-Family Dwelling: One (1) ADU and one (1) Junior ADU are allowed.
• Lots with Multiple Detached Units: One (1) ADU or one (1) JADU.
• Lots with Multifamily Development: On a lot with an existing duplex or multifamily building (3 units or more), one of the following is allowed:
  • A maximum of eight (8) detached ADUs are allowed on a lot with an existing multifamily building, not to exceed the number of existing units on the lot. 
  • Up to two detached ADUs are allowed on a lot that has a proposed multifamily dwelling.

Are ADUs subject to lot size requirements, coverage, and or density limitations?

No, any lot that is zoned residential and has an existing or proposed dwelling unit is eligible for an ADU. (See California Government Code Section 65852.2 and 65852.22) 

What is the maximum size of an ADU?

• Detached/ attached new construction
  • 850 square feet (studio or one-bedroom)
  • 1,200 square feet (one-bedroom +)
• Conversion ADU – May exceed size limitations. Note: An ADU created entirely through conversion with no modifications to the existing building envelope that exceeds the development standards for maximum size is allowed a physical addition of no more than 150 square feet for ingress and egress.
• JADU – 500 square feet 

Where can a JADU be established?

A JADU may only be established within existing or proposed single family dwellings, which includes attached garages. If a JADU is established in an attached garage, parking replacement is not required.

What are the required setbacks for a new construction ADU or an addition to an existing accessory building or structure that will be converted into an ADU?

A newly constructed ADU or an addition to an accessory building or structure that will be converted into an ADU must maintain 4-foot side and rear setbacks, and must adhere to applicable zoning district requirements for the front setback. 

Can architectural features (e.g. Bay windows, eaves, electrical equipment, etc.) project into the required setbacks?

Eaves and heating and cooling equipment may project 3 feet into the required setback. (See RMC 17.08)

What is the maximum height allowed for new construction ADUs or a new addition that is part of an ADU?

The maximum height of an ADU varies slightly. For detached ADUs:

• On a lot with an existing or proposed single- or multifamily unit, the maximum height is 16 feet.
• On a lot with an existing or proposed single- or multifamily unit that is within a half mile of a major transit stop or high-quality transit corridor (as defined in Section 21155 of the Public Resources Code) an additional two feet in height shall be allowed, for a maximum height of 18 feet.
• On a lot with an existing or proposed multifamily, multistory dwelling, the maximum height is 18 feet.

For Attached ADUs:

• 25 feet or the height limitation that applies to the primary dwelling described in the Rocklin Zoning Ordinance, whichever is lower.

How is the maximum height of an ADU measured?

The maximum height of an ADU is measured from finished grade to the highest point of the structure.

How much floor area can be added to an existing accessory building or structure that will be converted into an ADU?

Additional floor area may be added to an existing accessory building or structure as long as the size of the overall ADU does not exceed the maximum size of limits outlined in question 7. An ADU created entirely through conversion with no modifications to the existing building envelope that exceeds the development standards for maximum size limits outlined in question 7 is allowed a physical addition of no more than 150 square feet to allow for ingress and egress. The addition must comply with maximum height and setback requirements. (See BMC 23.306.040) 

Can an ADU have a porch? Does the porch count in the allowed square footage for the unit?

Yes, ADUs may have a porch.

Maximum floor area allowed depends on the underlying zone. Contact the Planning Department for more information.

Can an internal connection be maintained between the primary dwelling unit and the ADU/ JADU?

Yes, an internal connection can exist between the respective units, provided the connection is fire rated and is secured. If a separate bathroom is not included in a JADU, an internal connection must be provided.

How do I legalize an existing unpermitted ADU?

Unpermitted ADUs will be reviewed and considered as a new construction ADU for zoning purposes and are subject to the existing development standards in the zoning ordinance.

Can a commercial space within a mixed- use structure be converted into an ADU?

No, an existing commercial space cannot be converted into an ADU. (See California Government Code Section 65852.2 and 65852.22.) 

Parking

Is replacement parking required for ADUs? 

Replacement parking for existing dwelling unit(s) is not required, but is allowed when a garage, carport, covered parking structure or designated uncovered parking area is physically replaced by an ADU.

Is parking required for new ADUs and JADUs?

No.

Rental and Ownership

Can I rent the primary dwelling unit(s) and ADU to different parties?

Yes, the primary dwelling unit and the ADU may be rented to different parties. (See California Government Code Section 65852.2 and 65852.22)

Does the property owner have to live onsite?

On a property with an ADU, there is no owner occupancy requirement. On a property with a JADU, the owner must live in the primary residence or the JADU. (See California Government Code Section 65852.2 and 65852.22) 

Can an ADU be used as a short-term rental?

No.

Is an ADU required to have its own address?

Yes. An address will be assigned to the ADU as part of the building permit process. However, JADUs are not required to have a separate address. (See California Government Code Section 65852.2 and 65852.22.) 

Can an ADU be sold separately from the primary dwelling unit?

Except as provided in Section 65852.26, the ADU may not be sold or otherwise conveyed separate from the primary residence. (See California Government Code Section 65852.2, 65852.22, and 65852.26)

Can non-habitable amenities of a multifamily dwelling structure (i.e. garage, laundry room, storage space) be converted into an ADU?

Yes, provided that the conversion of these spaces does not conflict with existing lease agreements and that the amenity space is associated with the residential units. (See California Government Code Section 65852.2 and 65852.22