Accessory Dwelling Units

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The City of Hercules supports development of Accessory Dwelling Units (ADUs) and Junior Accessory Dwelling Units (JADUs), also known as granny or in-law units as an innovative, affordable, and effective option for adding much-needed missing middle housing. Please review the information below to learn more about our local requirements for developing an ADU or JADU.

General ADU/JADU Information

Location. ADUs are permitted in any residential or mixed-use zone that permits residential uses.

ADU. An ADU may be attached or detached from the primary dwelling, must have an exterior entrance separate from the primary dwelling, and must have complete independent living facilities for 1 or more persons, including permanent provisions for sleeping, living, eating, cooking, and sanitation.

JADU. A JADU is no more than 500 square feet in size and contained entirely within the walls of an existing or proposed single-family residence; it must include a cooking facility with appliances, and a food preparation counter and storage cabinets that are of reasonable size in relation to the size of the JADU. JADUs may share a bathroom with the primary residence and have an internal connection.

Statewide Exempt ADU. Are ADUs that have total floor area of no more than 800 square feet, with 4 feet rear and side setbacks, with a height limitation of 16 feet on single-family lots or 18 feet on multi-family lots. See Hercules Municipal Code Sec. 13-35.320(10)

Fire Sprinklers. Accessory dwelling units shall not be required to provide fire sprinklers if fire sprinklers are not required for the primary residence.

No Short Term Vacation Rentals. All accessory dwelling units shall only be rented for a term of more than 30 days.

Owner Occupancy Requirements for JADUs. The owner of a parcel with a single-family dwelling and a proposed junior accessory dwelling unit shall occupy as a principal residence either the primary dwelling or the accessory dwelling.

Design. An ADU must conform to the design characteristics of the existing residence or residences.

ADU Address. Detached ADUs require a new address.

Impact Fees. ADUs of less than 750 square feet are not subject to impact fees. ADUs of 750 or more square feet are subject to any fees for residential units required by the City’s Master Fee Schedule. Fees shall be charged in proportion to the square footage of the primary dwelling (e.g., a 1,000-square-foot ADU would be charged 50 percent of the applicable fee if the primary dwelling is 2,000 square feet).

Development Standards

Single-Family Lot Development Standards Number of Units - One converted or newly constructed ADU, and one JADU
	Conversion of Structure	Attached ADU	Detached ADU
Maximum Square Footage	No unit size limits apply to conversion of an existing accessory structure or a portion of the existing primary residence to an ADU	1 bedroom 850 sq ft 2+ bedrooms 1,000 sq ft	1 bedroom 850 sq ft 2+ bedrooms 1,000 sq ft
Front Setback	N/A	As required by applicable zoning district, except that front setbacks may not preclude the construction of a Statewide Exempt ADU	As required by applicable zoning district, except that front setbacks may not preclude the construction of a Statewide Exempt ADU
Side - Interior Setback	No setback is required for an ADU created within an existing living area or accessory structure or an ADU created in a new structure in the same location as an existing structure	4 feet minimum	4 feet minimum
Side - Corner Setback	No setback is required for an ADU created within an existing living area or accessory structure or an ADU created in a new structure in the same location as an existing structure	As required by applicable zoning district, except Statewide Exempt ADU may be located 4 feet from a corner lot line	As required by applicable zoning district, except Statewide Exempt ADU may be located 4 feet from a corner lot line
Rear Setback	No setback is required for an ADU created within an existing living area or accessory structure or an ADU created in a new structure in the same location as an existing structure	4 feet minimum	4 feet minimum
Height Limit	N/A	Applicable height limits of the zoning district	16 feet + plus 2 feet if needed to match roof pitch of existing dwelling
Parking	0 parking	Studio – 0 parking 1+ bedrooms – 1 parking	Studio – 0 parking 1+ bedrooms – 1 parking

Multi-Family Lot Development Standards (Multi-family means a lot containing two or more attached dwellings) Number of Units - Two detached ADUs and at least one interior ADU (converted from existing non-livable space) up to 25 percent of the number of units in the proposed or existing multifamily dwelling
	Interior Conversion	Attached ADU	Detached ADU
Maximum Square Footage	Must be converted from non-livable space, if no such area exists an interior ADU can’t be approved	1 bedroom 850 sq ft 2+ bedrooms 1000 sq ft	1 bedroom 850 sq ft 2+ bedrooms 1000 sq ft
Front Setback	N/A	As required by applicable zoning district, except that front setbacks may not preclude the construction of a Statewide Exempt ADU	As required by applicable zoning district, except that front setbacks may not preclude the construction of a Statewide Exempt ADU
Side - Interior Setback	N/A	4 feet	4 feet
Side - Corner Setback	N/A	As required by applicable zoning district, except Statewide Exempt ADU may be located 4 feet from a corner lot line	As required by applicable zoning district, except Statewide Exempt ADU may be located 4 feet from a corner lot line
Rear Setback	N/A	4 feet	4 feet
Height Limit	N/A	Applicable height limits of the zoning district	18 feet + plus 2 feet to match roof pitch of existing dwelling
Parking	0 parking	Studio – 0 parking 1+ bedrooms – 1 parking	Studio – 0 parking 1+ bedrooms – 1 parking

Application Process

A Building Permit is required for development of an ADU/JADU, with review by the Community Development Department.

Applicants shall provide a complete application package to Planning Division to begin the ministerial review process.

Download the ADU Handout and Checklist for complete submittal requirements.

Once complete and submitted to the Planning Department, please allow up to 30 days for completeness review. For more information, please contact the Planning Department.