Modesto Municipal Code Art. 5 Accessory Dwelling Units

This article implements the requirements of Government Code Section 66310 et seq.

(Ord. No. 3762-C.S., effective § 3, effective 5-11-23; Ord. No. 3787-C.S., § 4, effective 1-2-25)

(a) Accessory dwelling units (ADUs) may be created in any zone that allows single-family residential, multi-family residential, or mixed-use, or as expressly permitted in this article.

(b) Junior accessory dwelling units (JADUs) may be created only in zones that allow single-family residential on a lot with an existing or proposed single-family dwelling.

(c) ADUs and JADUs may only be rented in increments of thirty (30) days or more.

(d) An ADU includes an efficiency unit as defined in Section 17958.1 of the Health and Safety Code.

(e) An ADU includes a manufactured home, as defined in section 18007 of the Health and Safety Code.

(f) These regulations may be applicable to lots zoned for single-family residential uses and built with units in compliance with Senate Bill No. 9 (Chapter 162, Statues of 2021).

(g) An accessory dwelling unit (ADU) or junior accessory dwelling unit (JADU) conforming to the standards of this article shall:

(1) Be deemed to be an accessory use or accessory building.

(2) Be deemed a residential use that is consistent with the existing General Plan and zoning designation for the lot.

(3) Not be considered in the application of any local ordinance, policy, or program to limit residential growth.

(4) Not be considered to exceed the allowable density for the lot upon which the ADU or JADU is located.

(5) Except as provided in Government Code Section 66310 et. seq., an accessory dwelling unit may be rented separate from the primary residence but may not be sold or otherwise conveyed separate from the primary residence.

(Ord. No. 3762-C.S., effective § 3, effective 5-11-23; Ord. No. 3787-C.S., § 4, effective 1-2-25)

(a) Ministerial Approval Only. A local agency shall ministerially approve an application for a building permit for an ADU or JADU.

(1) Timeframe for Review. If there is an existing single-family or multi-family dwelling on the lot, the permitting agency shall either approve or deny the application within sixty (60) days from the date the permitting agency receives the completed application.

(i) If the applicant requests a delay, the sixty (60)-day time period shall be tolled for the period of the delay.

(2) If the local agency has not approved or denied the completed application within sixty (60) days, the application shall be deemed approved.

(3) If a building permit for an ADU or JADU is submitted with a permit application for a new single-family or multi-family dwelling on the lot, the permitting agency may delay approval or denial of the ADU or JADU application until the permitting agency either approves or denies the application to create the new single-family or multi-family dwelling.

(4) A demolition permit for a detached garage that will be replaced with an ADU, shall be reviewed with the application for the ADU and issued at the same time.

(i) Written notice or the posting of a placard for the demolition of a detached garage, per subparagraph (4), above, shall not be required, unless the subject property is located within an architecturally and historically significant historic district, or is listed on a local, statewide, or national register of historically significant structures.

(5) If the permitting agency denies an application for an ADU or JADU, the permitting agency shall, within the sixty (60) daytime-period, return in writing a full set of comments to the applicant with a list of items that are defective or deficient and a description of how the application can be remedied by the applicant.

(b) Fire Sprinklers. An ADU shall not be required to provide fire sprinklers if they are not required for the primary residence; and the construction of an ADU shall not trigger a requirement for fire sprinklers to be installed in the existing primary dwelling.

(c) An ADU shall not be required to provide a passageway in conjunction with the construction of an ADU.

(d) An ADU shall not be required, as a condition for ministerial approval, to correct nonconforming zoning conditions.

(e) Local building code requirements that apply to detached dwellings shall apply to ADUs, except that the construction of an ADU shall not constitute a Group R occupancy change under the local building code, as described in Section 310 of the California Building Code (Title 24 of the California Code of Regulations), unless the building official or enforcement agency of the local agency make a written finding based on substantial evidence in the record that the construction of the ADU could have a specific, adverse impact on public health and safety.

(1) Nothing in this clause shall be interpreted to prevent a local agency from changing the occupancy code of a space that was unhabitable space or was only permitted for nonresidential use and was subsequently converted for residential use pursuant to this section.

(f) No other local ordinance, policy, or regulation shall be the basis for the delay or denial of a building permit or use permit under this subdivision.

(g) Fees charged for the construction of accessory dwelling units shall be determined in accordance with Government Code Section 66324, as amended and renumbered from time to time.

(h) An ADU shall not be considered to be a new residential use for the purposes of calculating connection fees or capacity changes for utilities, including water and sewer service, unless the ADU was constructed in conjunction with a new single-family dwelling. The City may require a new or separate utility connection, as well as a corresponding connection fee or capacity charge, in accordance with Government Code Section 66324.

(i) The City shall not impose any impact fee upon the development of an ADU less than seven hundred fifty (750) square feet in floor area.

(j) An impact fee charged for an ADU of seven hundred fifty (750) square feet or more in floor area shall be charged proportionately in relation to the square footage of the primary dwelling unit.

(k) For an ADU of eight hundred (800) square feet or less, lot coverage as shown on Table 4.1-1 (Residential Development Standards) shall not apply.

(Ord. No. 3762-C.S.,§ 3, effective 5-11-23; Ord. No. 3787-C.S., § 4, effective 1-2-25)

(a) Attached. An ADU may be attached to a proposed or existing single-family dwelling or multi-family dwelling.

(b) Detached. An ADU may be detached (free-standing) from a proposed or existing single-family or multi-family dwelling on a lot, (e.g., a new-construction, detached ADU).

(c) Converted. An ADU may be located within a proposed or existing single-family dwelling (e.g., an existing attached garage), or other living space to be converted to an ADU (e.g., master bedroom suite); or an existing detached accessory structure to be converted to an ADU.

(1) For multi-family dwellings, an ADU may be located in areas currently not used for living spaces, (e.g., storage room, laundry room), or in an existing (free-standing) accessory building on the lot.

(d) Junior ADU (JADU). A JADU is a special type of ADU that is not more than five hundred (500) square feet in size and is contained entirely within the walls of an existing or proposed single-family residence. JADUs may only be created in single-family zones.

(Ord. No. 3762-C.S., effective § 3, effective 5-11-23; Ord. No. 3787-C.S., § 4, effective 1-2-25)

(a) Lots with a Single-family Dwelling or Duplex. On a lot developed with an existing or proposed single-family dwelling or duplex, an applicant may choose from any of the following ADU types (i.e., attached, detached, converted) or a JADU, or a combination thereof not to exceed two (2) additional units beyond the primary single-family residence.

(1) An attached (new construction) ADU meeting the requirements of this chapter.

(2) A detached (new construction) ADU:

(i) Minimum four (4) foot side and four (4) foot rear yard setbacks are required.

(3) A converted ADU may be located within an existing single-family dwelling (i.e., in living space to be converted to an ADU, e.g., a master bedroom suite), or within an existing detached accessory structure (e.g., a detached garage).

(i) The ADU located within an existing or proposed single-family dwelling must have exterior access.

(ii) The side and rear setbacks of the existing accessory structure to be converted must be sufficient for fire and safety.

(4) One (1) junior accessory dwelling unit (JADU) is allowed per lot zoned for single-family residential, where there is only one (1) existing or one (1) proposed single-family dwelling.

(i) Junior accessory dwelling units shall conform to the requirements in Section 10-4.509, below.

(b) Lots with Multi-family Residential Dwellings.

(1) Multiple accessory dwelling units are allowed within the portions of existing multi-family dwelling structures that are not used as livable space, including but not limited to, storage rooms, boiler rooms, passageway, attics, basements, or garages, if each unit complies with state building standards for dwellings.

(2) The number of ADUs shall not exceed twenty-five (25) percent of the existing multi-family units, except that at least one (1) ADU is allowed.

(3) Not more than two (2) detached ADUs may be added to a lot that has a proposed multi-family dwelling, and not more than eight (8) detached ADUs may be added to a lot that has an existing multi-family dwelling.

(c) ADUs Developed on a Lot With an Existing or Proposed Place of Worship.

(1) An ADU may be developed on a lot, meeting the following requirements:

(i) Zoned Residential or Commercial, and excluding the Industrial Zones (C-M, M-1, and M-2);

(ii) Developed with an existing or proposed place of worship; and

(iii) Where the church or place of worship meets the Internal Revenue Service (IRS) requirements for tax exempt status under Internal Revenue Code (IRC) Section 501 (c)(3).

(2) Not more than two (2) detached ADUs may be built.

(3) Each ADU may not exceed twelve hundred (1,200) square feet in floor area.

(4) Each ADU shall meet the required front setbacks of the respective zoning district.

(5) Each ADU shall meet the required street-side setbacks of the respective zoning district.

(6) Each ADU shall have a minimum four (4) foot interior side and rear yard setbacks.

(7) No additional off-street parking is required for the ADUs, if at least one (1) existing off-street parking space is reserved for tenants in each proposed ADU.

(8) The ADUs shall have a maximum height of sixteen (16) feet.

(Ord. No. 3762-C.S., effective § 3, effective 5-11-23; Ord. No. 3787-C.S., § 4, effective 1-2-25; Ord. No. 3787-C.S., § 4, effective 1-2-25; Ord. No. 3797-C.S, § 6, effective 6-24-25)

(a) Attached ADUs. The total floor area of an attached accessory dwelling unit shall not exceed fifty (50) percent of the primary dwelling. For a duplex, the total floor area of an attached accessory dwelling unit shall not exceed fifty (50) percent of the primary unit or units that the accessory dwelling unit is proposed to be attached to. This limitation shall not preclude development of an attached ADU of up to eight hundred (800) square feet.

(b) Detached ADUs.

(1) The total floor area for a detached ADU shall not exceed twelve hundred (1,200) square feet.

(2) A detached ADU shall not exceed the square footage (in floor area) of the existing or proposed single-family dwelling.

(c) Converted ADUs.

(1) When an existing detached accessory structure is converted to an ADU, a maximum one-hundred-fifty (150) square-foot expansion beyond the dimensions of the existing accessory structure is allowed, provided the expansion is used solely for accommodating ingress and egress.

(2) Any expansion to an existing structure that is nonconforming as to its setbacks, shall provide a minimum four (4) foot interior side yard and four (4) foot rear yard setbacks.

(Ord. No. 3762-C.S., effective § 3, effective 5-11-23; Ord. No. 3787-C.S., § 4, effective 1-2-25; Ord. No. 3797-C.S, § 7, effective 6-24-25)

(a) Lots with a Single-family Dwelling.

(1) A height limit of sixteen (16) feet for a detached accessory dwelling unit on a lot with an existing or proposed single-family; or

(2) A height limit of eighteen (18) feet for a detached accessory dwelling unit on a lot with an existing or proposed single-family dwelling that is within one-half (0.5) of one (1) mile walking distance of a major transit stop or a high-quality transit corridor, as those terms are defined in Section 2115 of the Public Resources Code.

(3) An additional two (2) feet of height is allowed to accommodate a roof pitch on an accessory dwelling unit that is aligned with the roof pitch of the primary dwelling.

(4) For an ADU that is attached to a primary dwelling, a maximum height of twenty-five (25) feet or the height limitation in the zone that applies to the single-family dwelling, whichever is lower. Notwithstanding the foregoing, an ADU shall not exceed two (2) stories.

(b) Lots with Multi-family Dwellings.

(1) A height limit of sixteen (16) feet for a detached accessory dwelling unit on a lot with an existing or proposed multi-family dwelling; or

(2) A height of eighteen (18) feet for a detached accessory dwelling unit on a lot with an existing or proposed, multi-family dwelling unit, that is within one-half of one mile walking distance of a major transit stop or high quality transit corridor, as those terms are defined in Section 2115 of the Public Resources Code.

(3) An additional two (2) feet of height is allowed to accommodate a roof pitch on the accessory dwelling unit that is aligned with the roof pitch of the primary multi-family dwelling unit.

(4) A height of eighteen (18) feet on a lot with an existing or proposed multi-family, multi-story, dwelling.

(Ord. No. 3762-C.S., effective § 3, effective 5-11-23; Ord. No. 3787-C.S., § 4, effective 1-2-25)

(a) No more than one (1) off-street parking space shall be required for an accessory dwelling unit.

(1) Parking may be tandem in an existing driveway.

(2) An uncovered off-street parking space, for an accessory dwelling unit, may be located, on a paved surface, in either a required front setback (existing driveway) or (if a lot has alley access) in a required rear setback.

(b) When a garage, carport, or other covered parking structure is demolished in conjunction with the construction of an accessory dwelling unit or is converted to an accessory dwelling unit, the lost off-street parking is not required to be replaced.

(c) No parking is required for an ADU or a JADU unit if:

(1) The unit is within one-half (0.5) mile walking distance of public transit.

(2) The accessory dwelling unit is within an architecturally and historically significant district.

(3) The accessory dwelling unit is part of the proposed or existing primary residence or an accessory structure.

(4) When on-street parking permits are required but not offered to the occupant of the accessory dwelling unit.

(5) When there is a car share vehicle located within one (1) block of the accessory dwelling unit.

(6) When a permit application for an ADU (in compliance with these requirements) is submitted as part of a permit application to create a new single-family, or new multi-family dwelling on the same lot.

(Ord. No. 3762-C.S., effective § 3, effective 5-11-23; Ord. No. 3787-C.S., § 4, effective 1-2-25)

Editor's note— Ord. No. 3787-C.S., § 4, adopted December 3, 2024, effective 1-2-25, renumbered the former §§ 10-4.508, 10-4.509 as §§ 10-4.509, 10-4.508, respectively and enacted amended §§ 10-4.508, 10-4.509 as set out herein. The historical notation has been retained with the amended provisions for reference purposes.

(a) A junior accessory dwelling unit (JADU) shall be contained within the walls of the existing or proposed single-family residence.

(1) For the purposes of this section, contained within, a single-family residence includes the conversion of an attached garage.

(b) A JADU shall not exceed five-hundred (500) square feet in area.

(c) The JADU shall include a separate entrance from the main entrance to the existing or proposed single-family dwelling.

(d) A (JADU) may include separate sanitation facilities or may share sanitation facilities with the existing single-family residence. If a JADU does not include a separate bathroom, the JADU shall include a separate entrance from the main entrance to the structure, with an interior entry to the main living area.

(e) A JADU unit shall have an efficiency kitchen which includes all of the following:

(1) A cooking facility with appliances;

(2) A food preparation counter; and

(3) Storage cabinets of a reasonable size in relation to the size of the JADU.

(f) Prior to final inspection of a JADU, the property owner shall record a notice of condition (deed restriction), which shall run with the land, specifying that owner shall occupy either the JADU or the remaining portion of the single-family residence at all times, unless the owner is a governmental agency, land trust, or housing organization.

(g) Prior to final inspection of a JADU, the property owner shall record with the City a deed restriction, which shall run with the land, that shall include both of the following:

(1) A prohibition on the sale of the JADU unit separate from the sale of the single-family residence, including a statement that the deed restriction may be enforced against future purchasers.

(2) A restriction on the size and attributes of the JADU unit that conforms with Government Code Section 66310 et seq.

(h) A JADU shall not be sold separately from the single-family residence.

(Ord. No. 3762-C.S., effective § 3, effective 5-11-23; Ord. No. 3787-C.S., § 4, effective 1-2-25)

Editor's note— See editor's note at 10-4.508.

(a) The maintenance of a single-family dwelling appearance is encouraged through means such as:

(1) For an attached ADU or JADU, locating the second unit entrance to the side or rear of the main building so it is not readily visible from the street.

(2) Employing construction materials and architectural styles which blend the units so they appear as a single residence (if attached) or as single residence and accessory building, if detached.

(b) Where a second story accessory dwelling unit (ADU) is built adjacent a rear or side yard of a lot developed with a one (1) story, single-family residential dwelling, any walls of the accessory dwelling unit that could provide unobstructed views of a neighboring rear yard or actively used side yard shall have either no windows or windows with a bottom sill located at least five (5) feet eight (8) inches from the finished floor of the second story. This does not apply to a window required by the Building Code to be usable for accessible emergency access. This limitation shall not preclude the development of an ADU.

(c) The City Council may designate, from time to time, by resolution, areas within which accessory dwelling units will not be permitted due to infrastructure constraints relating to water and sanitary sewer.

(Ord. No. 3762-C.S., effective § 3, effective 5-11-23; Ord. No. 3787-C.S., § 4, effective 1-2-25)

Notwithstanding anything in this article to the contrary, the City shall ministerially approve the types of ADUs specified in Government Code Section 66323.

(Ord. No. 3787-C.S., § 4, effective 1-2-25)

In the event of a conflict between this Code and the requirements of Government Code Section 66310 et seq., as amended and renumbered from time to time, the requirements of State law shall apply.

(Ord. No. 3787-C.S., § 4, effective 1-2-25)