A Guide to Building Accessory Dwelling Units
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Part 1: ADU Manual Part 2: Pre-Approved ADUs Part 3: Appendix
1.1 Introduction 2.1 Introduction 3.1 Contacts and Resources
1.2 Regulations 2.2 Plan Options 3.2 FAQs
1.3 Development Standards
1.4 Considerations
1.5 Permitting
Table of Contents
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Part 1: Accessory Dwelling Unit Manual 1
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An accessory dwelling unit (ADU) is an attached or a detached residential dwelling unit which provides complete independent living facilities for one or more persons. It shall include permanent provisions for living, sleeping, eating, cooking, and sanitation on the same parcel which the primary single-family or multifamily dwelling unit is situated. An accessory dwelling unit may also include the following: An efficiency unit, as defined in Section 17958.1 of the Health and Safety Code, and a manufactured home, as defined in Section 18007 of the Health and Safety Code. In 2016, the State approved new regulations pertaining to accessory dwelling units, which became effective on January 1, 2017. The intent of the new regulations was to facilitate and expedite the construction of new dwelling units that are secondary to a primary single-family or multifamily dwelling on the same lot to increase affordable housing in California. Cities were then encouraged to amend local zoning ordinances to provide a means of facilitating accessory dwelling units (ADUs) under local development standards. The City responded by adopting an ordinance in 2018 (amended in 2020) related to ADUs. The City’s ordinance provides relief from several zoning standards, the standards applicable to ADUs are outlined in greater detail in this guide. Additional amendments to California law related to ADUs became effective January 1, 2020 which included several changes including the allowance of an ADU on multifamily lots, impact fee exemptions, allowances for garage conversions, eliminated minimum lot size requirements, and reduced the maximum application review time from 120 days to 60 days. Additional legislative amendments became law in 2021 and 2022. This guide is a resource for residents interested in adding an ADU to their property. The guide contains three parts: (1) An informational guide on the process of building an ADU, (2) a selection of “pre-approved” ADU plans that are available at no cost, and (3) an appendix with contact information and additional resources. ADUs provide many benefits for the municipality, the owners, and for prospective renters. If you are planning to build an ADU, there are many alternatives to consider. This section discusses some of these alternatives such as the intended use of the unit, the size and location of the unit, construction methods, and professional help in the process.
ADUs can be used in many ways. These units provide flexible space for the owners as they can be used as rental properties, home offices, or guest rooms. The size of these units is conducive to multigenerational housing, and provides options for families to grow and age in place. As rental units, ADUs help diversify the housing options within the existing community, and the rental income helps owners offset their housing costs.
Introduction to Accessory Dwelling Units 1.1
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State laws have changed drastically in recent years to support the construction of ADUs throughout California and in addition the City of Manteca has taken several measures to help promote the construction of new units, as well as to legalize previously constructed and unpermitted units through the City’s Development Services Department. Senate Bill 1226 (2018) As of January 1, 2019, homeowners who created accessory dwelling units (ADUs) without the required building permits may have the opportunity to bring their ADUs into compliance.
For ADUs that were constructed without building permits, local building officials now have the option to inspect the ADU and apply the building standards that were in effect at the time the unit was constructed. This bill, with application of appropriate building codes, may allow issuance of a building permit for the residential unit. (See California Health and Safety Code Section 17958.12) Other State Laws for ADUs
California Senate Bill 1069 (2016) amended Planning and Zoning law to ease restrictions on ADUs in order to address the state’s housing shortage. The Legislature further updated ADU law effective January 1, 2018, to clarify and improve various provisions to promote the development of ADUs. These include allowing ADUs to be built concurrently with a single-family home, opening areas where ADUs can be built to include all zoning districts that allow single-family uses, modifying fees from utilities, such as special districts and water corporations, and reducing parking requirements. State legislation that took effect January 1, 2020 and January 1, 2021 gave California cities more flexibility and latitude for allowing homeowners to build ADUs. Several bills were introduced that clarified previous legislation and further eased the requirements to construct and ADU. Each of these land use bills make it easier than ever for homeowners to take advantage of this attractive opportunity. Recent state legislation is codified in California Government Code Section 65852.2 and 65852.22.
Regulations 1.2
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ADUs come in many shapes and sizes but are always a self-contained home that is smaller than the main house and legally part of the same property. An ADU always contains a kitchen, bathroom, and place to sleep. ADUs can range from efficiency studio units to 1,200-square foot units with multiple bedrooms. Detached, attached, interior conversions, and above garage accessory units can be either new construction or converted space. A building permit is required to build any accessory dwelling unit. It is recommended that you visit the Development Services Department to talk with staff about your project while in the planning stages. Staff can help you determine if an ADU is allowed on your property and to discuss zoning standards that are applicable to your project. They can also help answer questions about the building code and applicable construction standards, utilities, and fees. Zoning Standards ADUs are permitted on all residentially zoned properties that are occupied with a single-family dwelling unit or will be improved with a single-family dwelling unit prior to or at the same time as the ADU construction. One ADU is allowed per single-family parcel. ADUs are also permitted on parcels with multifamily development. An attached ADU is allowed up to 1,200 square feet in area but no more than 50% of the existing living area, whichever is less. In some specific circumstances, detached ADUs are allowed up to 1,200 square feet. There are no off-street parking requirements for ADUs and if a garage is converted to an ADU, replacement parking is not required.
Development Standards 1.3
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4 DEVELOPMENT STANDARDS FOR ACCESSORY DWELLING UNITS
ATTACHED DETACHED INTERNAL
Addition to esidence Structure
separated from the
residence
Conversion inside existing
residence or xisting
accessory structure
Min. Lot Size No limitations No limitations No limitations Max. Unit Size No more than 50% of existing living area, or 850 sq
ft, or 1,000 sq ft for a 1 bedroom, or 1,200 for accessible unit
Max. floor area of 850 sq ft,
or 1,000 sq ft for a 1 bedroom, or 1,200 for accessible unit Max. floor area of 850 sq
ft, or 1,000 sq ft for a 1
bedroom, or 1,200 for accessible unit
Min. Setback
Front
Side
Rear
Same as required for the primary structure by the zoning district 4-feet 4-feet
N/A – Existing Structure
Sufficient for fire access Sufficient for fire access
Max. Height 16 feet N/A – Existing Structure Site Coverage ADU structure is not included in the calculation of site coverage allowed by the applicable zoning district
N/A – Existing Structure
Off-Street Parking None required for ADU
None required for ADU and no replacement parking with garage conversion Max ADUs/Lot One (1) ADU per lot, two (2) when parcel has existing multifamily building Access Independent exterior entrance to the ADU is required Density ADU shall not be included in the calculation or determination of lot density Type of ADUSeparation Per California Building Code and Fire Code N/A—Existing Structure 16 feet
Types of ADUs Allowed
Attached Detached Internal / Conversion
Design Standards
If exterior alterations, additions, or construction of a new structure is required for an ADU, the ADU improvements shall be architecturally compatible with the main dwelling unit. No portion of an ADU balcony, deck, or open stair landing that faces the rear lot line or the side nearest to the ADU shall be higher than three feet from the ground. For accessory dwelling units that do not meet the zoning designation’s setback for the main dwelling unit, no portion of any window that faces the lot line where the setback requirement for the main dwelling unit is not met may extend above 10 feet from the ground.
Occupancy and Ownership
The property owner is not required to reside in either the ADU or main dwelling unit. An ADU may be rented, although rental is not required (no Short-Term Rental). The ADU shall not be sold separately from the main dwelling unit. Floodplain Development: ADUs are required to meet development standards of 100-year floodplains. Please contact the Building Safety Division at (209) 456-8500 to determine if the ADU is located in a 100-year floodplain.
Fire Sprinklers: Fire sprinklers are not required in an ADU, unless they are required in the main dwelling unit.
Consultation with Fire Prevention is recommended and may be contacted at (209) 456-8500.
Sanitary Sewer and Water Utilities: Separate sanitary sewer and water connections between the ADU and the public utility mains are not required, provided that the existing on-site utilities can be extended from the existing main dwelling unit to the ADU.
If the property owner requests separate sanitary sewer and water utility connections for the ADU, then all connection improvements and associated connection fees shall be required. The Engineering Department may be contacted at (209) 456-8460 for further information.
Fees:
City Public Facilities Fees are not applied on building permits for the construction of an ADU. If the property owner requests separate utility connections for the ADU, then utility connection fees are required.
Pass-thru fees that the city collects on behalf of other agencies may apply.
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4 Size and Location
ADUs can be built as detached or attached units to the primary residence, within an existing home or accessory structure, or as a garage conversion. The City’s ADU regulations allow for a range of sizes, from studios up to 1,200 sf. The zoning of your property and the size of your existing lot and house will be determining factors in how large of an ADU you can build.
Considerations 1.4
Design Professionals Any of the following design professionals can assist the preparation of construction plans for an ADU. Architect Architects are professionals licensed by the state whom have a degree in architecture and have passed a series of licensing exams. Architects are legally responsible for the work they design. Architects may provide a range of services including full-service from the initial concept to final construction. This can include coordinating with additional consultants such as structural engineers, surveyors, civil engineers, contractors, or any other project related consultants. DesignerDesigners can come from varying backgrounds and skillsets. Most designers have a design-based education and/or work experience, but none are professionally licensed. The services designers provide are dependent upon the level of their experience in the design, engineering, and construction fields. Civil Engineer Civil Engineers work with the design, construction, and maintenance of natural and built environments. This can include residential, commercial, industrial, transportation, and infrastructure projects. A civil engineer can provide drafting, structural, grading, and Stormwater services.
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4 Types of Construction
Timber Frame Timber frame, or stick-built construction, is the traditional method of home construction. This method is done on-site and relies on wooden beams for its basic construction, with more narrow timber beams in between them. Timber framed homes often leave a portion of the wood timber exposed as part of the design aesthetic, in addition to its structural purpose. Modular Modular construction relies on pieces of the house or ADU being fabricated offsite, and then being delivered to the building site. The prefabricated pieces are delivered to the site and placed into position, either by hand or with a crane. Manufactured Manufactured construction is a process where an entire house or ADU, or sections of them, are predominantly built and assembled in factories. The entire unit, or the sections, is then transported to the building site and assembled.
Design/Build A design/build firm will design and construct your ADU. Design/build firms are usually headed by a licensed architect or contractor. There are no standards for design/build firms, so the level of services they provide varies depending on the skill set of the owner and staff. The staff is usually a collection of designers who provide design services for small scale projects. Manufacturer Modular and manufactured homes can be an efficient way of constructing your ADU. Manufacturers of these homes are monitored by the state of California, and a contractor is required for the on-site foundation work, utility hookups, and placement or assembly of the unit. Most manufacturers offer a variety of options for homeowners to customize their unit. This method of construction simplifies the design process and generally takes the least amount of time from conception to completion.
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4 Permit Center
A visit to the City’s Permit Center is a great first step towards constructing an ADU on your property. City Staff are available to guide you and answer your questions regarding your property, building plans, or the construction process. Please visit the Development Services Department for additional information on how to submit an application for new construction of an attached or detached ADU. PlanningPlanning staff can provide information about your property, including the zoning and lot size, which are critical in determining the type and size of ADU you can build. A Planner can also assist you with all of the other development standards that may influence the design of your ADU. Building Building staff will ultimately issue your permit to construct and occupy your ADU. The staff can walk you through the permitting and inspection process, and provide you with a list of building codes and drawing requirements that you or your consultants will need to consider prior to applying. Engineering Engineering staff can help you with questions about property lines, right-of-ways, grading, storm water, and utility and drainage easements. Only a professional survey of your property can accurately determine where all of the boundaries lie, and it is recommended that one be conducted as part of your planning process. Fire Fire Prevention staff are available to answer questions about fire sprinkler requirements for your ADU. Generally, fire sprinklers are not required for an ADU unless the main house has fire sprinklers. Public Works Public Works staff are available to answer questions about existing utilities on or around your site, and sewer & water connection requirements for your ADU.
Permitting 1.5
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4 Plan Check Fees Paid /
Plans Submitted
Route for
Review
Engineering
Plans Approved
Plans Returned
for Corrections
Plans Corrected
and Resubmitted
Public
Works
Planning Building
Remaining Fees
Paid Permit Issued Begin Construction Field Inspections Final Occupancy
Building Permit Process
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4 Part 2: Pre-Approved Accessory Dwelling Units 2
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The city has developed a program to encourage the construction of ADUs by offering a selection of pre-approved ADU building plans. These permit-ready plans are complete sets of construction drawings to the latest codes. These drawing packages are pre-approved by the Building Safety Division and are available “off-the-shelf” at no cost. The selection of permitready plans includes a studio, 1-bedroom, and 2-bedroom option. This program aims to assist in the construction of ADUs to address the citywide housing shortage by providing complete construction drawings, expediting the process, and reducing preconstruction costs. The permit-ready plans were designed with simplicity and cost in mind. The plans have simple floor plan layouts, simple roof designs, and utilize conventional construction techniques to reduce the cost and length of construction. These plans were developed collaboratively with the City of Stockon and some drafting assistance from the students at the Lincoln High School Engineering and Construction Academy. You are encouraged to contact the Planning Division regarding any specific design requirements early on in the process. You can contact Planning at (209) 456- 8500 or by visiting the Permit Center Counter.
If a permit-ready ADU plan is chosen for your project, a Site Plan must be provided with the permit-ready plans.
The Site Plan shall include the following:
Must be drawn to scale Show property lines, sidewalks, driveways Location of the main residence Location of the Proposed ADU Distance from structures to property lines Distance between structures on site Approximate location of existing and new utilities Location of electrical service Introduction to Permit Ready ADUs 2.1
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Sample Site Plan
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1-Bedroom Option
1-Bedroom | 1-Bath | 625 SF
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2-Bedroom Option
2-Bedroom | 1-Bath | 745 SF
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Studio Option
Studio | 1-Bath | 435 SF
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Part 3: Appendix 3
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Contacts and Resources 3.1
Contacts Development Services
Planning
(209) 456-8500 Building (209) 456-8500
Fire Prevention (209) 456-8340 Engineering (209) 456-8460 Resources American Institute of Architects (AIA) www.aia.org Building Industry Association (BIA) http://biagv.org/ California Board for Professional Engineers and Land Surveyors www.bpelsg.ca.gov California Building Standards Commission www.bsc.ca.gov/Home.aspx California Department of Housing and Community Development (HCD): Second Unit Resources www.hcd.ca.gov/policy-research/ AccessoryDwellingUnits.shtml California Energy Commission www.energy.ca.gov California State Fire Marshal: Bulletin 17-001 http://osfm.fire.ca.gov/informationbulletin/pdf/2017/IB_17-001_Accessory_Dwelling_Units.pdf Contractors State License Board www.cslb.ca.gov Division of the State Architect www.dgs.ca.gov/dsa/Home.aspx Manteca Municipal Code http://qcode.us/codes/manteca/ International Code Council (ICC) www.iccsafe.org San Joaquin County Assessor https://www.sjgov.org/department/assr/
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4 1. HOW MUCH WILL MY ADU COST?
Since the size and construction of each ADU will differ, it is impossible to estimate the cost of your ADU. The cost per-square-foot of an ADU is likely to be the same as any new residential construction; builders and architects can give you rough estimates. 2. HOW MUCH WILL MY ADU PERMIT COST? Building permit fees are based on the cost of materials and labor to complete the project, known as the project valuation. Since the size and construction of each ADU will differ, the building permit fees are variable. A typical ADU building permit will range between $5,000 - $7,000. 3. ARE THERE OTHER FEES IN ADDITION TO THE CITY PERMIT FEES? There may be additional fees owed to outside agencies. New residential construction is subject to school district developer fees, you would be responsible to pay those fees directly to the applicable school district. There are two school districts in Manteca, you should contact the district for your area for an estimate. The California Water Service is the water purveyor for portions of the city. You should contact Cal-Water directly to inquire about their fees for a new ADU. Additional water/sewer connection fees are generally not applicable for ADUs if tapping into the same lines as the main house.
4. DOES MY ADU HAVE TO MATCH MY EXISTING HOUSE? The ADU improvements shall be architecturally compatible with the main dwelling unit. 5. MUST THE HOMEOWNER LIVE ON THE PROPERTY? No, both the existing house and the ADU can be rental units. 6. CAN I SELL MY ADU? No, you can only sell your house and ADU together. ADUs can be rental units or occupied by the homeowner or family members. 7. DO I HAVE TO PROVIDE OFF-STREET PARKING FOR MY ADU? No, there are no off-street parking requirements for ADUs and if a garage is converted to an ADU, replacement parking is not required. 8. CAN I LEGALIZE AN UNPERMITTED ADU ON MY LOT? Although this guide focuses on new construction, you may be able to get permits that will legalize an existing unit on your property. You can contact the Community Development Department for more information.
9. HOW BIG CAN I MAKE MY ADU? There are some limits on the size of an ADU, based on the size of your lot and existing house. An attached ADU cannot be bigger than 50% of the existing house. A detached ADU cannot exceed 1,200 sq. ft. 10. MY LOT SEEMS TOO SMALL OR UNUSUAL IN SHAPE. CAN I STILL BUILD AN ADU? Most lots are unique in shape and size, this guide addresses the most common conditions. There are various types of ADUs that work on different lots. For example, if a detached ADU will not fit in your backyard, you might choose to attach a new ADU unit to your current house. Or, you may choose to construct an ADU above your existing garage. You are encouraged to discuss the options available for your specific lot with the city Planning Department. 11. ARE FIRE SPRINKLERS REQUIRED FOR MY ADU? Depends. ADUs are not required to be sprinklered if the primary residence does not have fire sprinklers. For example, a garage conversion to an ADU would not have to install fire sprinklers if the main residence isn’t sprinklered. However, if a new main residence and ADU were constructed together, sprinklers would be required in both units because they would be required in the main residence per the California Residential Code.
Frequently Asked Questions 3.3
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