Accessory Dwelling Units


Accessory Dwelling Units

Accessory Dwelling Units (“ADU”) have been known by many names: granny flats, second units, in-law units, backyard cottages, and more. ADUs are an innovative, affordable, and effective option for adding much-needed housing in California.

Please click on the Accessory Dwelling Unit Handbook (click here) for further information about ADU size and height limits, setback requirements, parking requirements or exemptions, and other design regulations. 

About an ADU

ADUs provide independent living quarters for one household on the same lot as the primary single-family dwelling. The ADU provides full facilities for sleeping, eating, cooking, and sanitation. The ADU may be detached, attached, or a converted structure located within the living areas of the primary dwelling unit on the lot.

  • Detached: The ADU structure is detached from the primary dwelling unit
  • Attached: The ADU structure is attached to the primary dwelling unit
  • Converted: The ADU within the existing primary dwelling unit or the ADU was established through the conversion of an accessory structure, for example, a garage or pool house.

Image of the types of ADUs


Junior ADUs

Junior Accessory Dwelling Units (“Junior ADU”) are allowed to be created within the walls of a proposed or existing single-family residence and shall contain no more than 500 square-feet. Junior ADUs offer additional housing options. They may share central systems, contain a basic kitchen utilizing small plug-in appliances, may share a bathroom with the primary dwelling, all to reduce development costs. Junior ADUs present no additional stress on utility services or infrastructure because they simply re-purpose existing space within the residence and do not expand the dwelling’s occupancy.

Please click on the Accessory Dwelling Unit Handbook (click here) for further information about height limits, setback requirements, parking requirements or exemptions, and other design regulations. 

What are the benefits of ADUs?

  • Affordability: ADUs are an affordable type of home to construct in California because they do not require paying for land, major new infrastructure, structured parking, or elevators.
  • Efficiency: ADUs can provide as much living space as many newly-built apartments and condominiums, and they’re suited well for couples, small families, friends, young people, and seniors.
  • Cost-Effective: ADUs are built with cost-effective wood frame construction, which is significantly less costly than homes in new multifamily infill buildings. ADUs also use less energy and resources (electricity, water, etc.) than larger full-size homes. 
  • Income: ADUs can provide a source of income for homeowners. ADUs can also increase the property value. 
  • Flexibility: ADUs give homeowners the flexibility to share independent living areas with family members and others, allowing seniors to age in place as they require more care.
  • Privacy: ADUs allow extended families to be near one another while maintaining privacy.
  • Housing options: ADUs provide a method to build more housing quickly, within existing neighborhoods while preserving neighborhood character, and without increasing density. Building a new ADU usually takes a few months, as opposed to a new housing subdivision that could take two years or more. 

Image for life cycle of ADUs

Different Types of ADUs

A) Detached ADUs

Image of detached ADU

Image of detached ADU

Image of detached ADU

Image of detached ADU

Image of detached ADU


B) Attached ADUs

Image of attached ADU

Image of attached ADU


C) ADUs above a garage

Image of ADU above garage

Image of ADU above garage


D) Junior ADU

Image of interior Junior ADU

Image of interior Junior ADU

Exhibit of detached ADU and Junior ADU

General Requirements

The following list is provided as an overview of the general requirements in State ADU law, but may not list all applicable regulations for your particular project.

Please read and review the Accessory Dwelling Unit Handbook provided by HCD – see link to PDF document at right. 

Number of ADUs per lot:

Single-Family Residential Lots:

One (1) ADU, attached or detached, on a lot with an existing or proposed single-family dwelling; and

One (1) Junior ADU, within an existing or proposed single-family dwelling.
Lots with multiple detached single-family dwellings are not eligible to have Junior ADUs.
Junior ADUs are not allowed in accessory structures.

Multi-Family Residential Lots:

Up to two (2) detached ADUs on a lot with multifamily dwellings; and

One (1) ADU within portions of multifamily structures that are not used as livable space, up to 25% of the existing floor space.

Maximum ADU Size

Detached ADU: 1,200 square-feet maximum.

Attached ADU: up to 50% of the floor area of the existing primary dwelling, and at least 800 square-feet minimum. 

  • ADUs are allowed to add up to 150 square feet beyond the physical dimensions of the existing accessory structure to provide for ingress.

Junior ADU: 500 square-feet maximum.

  • Junior ADU is required to be created within the single-family residence.
  • Junior ADU is not allowed to add up to 150 square-feet beyond the physical dimensions of the existing structure.

Setbacks for ADUs:

Front yard: 25 feet minimum in most single-family residential districts (R-1, R-E, R-S, R-A, R-A-A, R-R, R-R-A, A-1 and A-2). Front setbacks may vary for corner lots, key lots, reverse corner lots, etc. (please refer to the zoning district standards listed in RMC Title 18 – Zoning Regulations).

Side yard: 4 feet maximum

Rear yard: 4 feet maximum

Converting an existing structure to ADU:

  • A local agency may allow the expansion of a detached structure being converted into an ADU when the existing structure does not have four-foot rear and side setbacks.
  • A local agency may allow the expansion area of a detached structure being converted into an ADU to have no setbacks, or setbacks of less than four feet, if the existing structure has no setbacks, or has setbacks of less than four feet.
  • A local agency shall not require setbacks of more than four feet for the expanded area of a detached structure being converted into an ADU.

Other considerations for setbacks:

  • Setbacks may also account for utility easements or recorded setbacks.

Definitions in the Redlands Municipal Code:

ADU Height Limit:

No less than 16 feet (minimum).

Maximum of 2-1/2 stories and 35 feet in most single-family residential districts (R-1, R-E, R-S, R-A, R-A-A, R-R, R-R-A, A-1 and A-2) and the R-2 district. Please refer to the height limits for the subject property listed in RMC Title 18 – Zoning Regulations.

Definitions in the Redlands Municipal Code:  “Building Height” – see RMC 18.08.115

Parking for ADUs:

One (1) parking space per unit or bedroom, whichever is less.

  • These spaces may be provided as tandem parking on a driveway (tandem parking means two or more automobiles that are parked on a driveway or in any other location on a lot, lined up behind one another).
  • When a garage, carport, or covered parking structure is demolished in conjunction with the construction of an ADU, or converted to an ADU, the local agency shall not require that those off-street parking spaces for the primary unit be replaced.
  • Off-street parking spaces for the ADU shall be permitted in setback areas in locations determined by the local agency, or through tandem parking, unless specific findings are made (specific findings must be based on specific site or regional topographical or fire and life safety conditions).
  • Guest parking spaces shall not be required for ADUs.

Exemptions from ADU parking requirements:
1) ADU is located within one-half mile walking distance of public transit
2) ADU is located within an architecturally and historically significant historic district.
3) ADU 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 ADU.
5) When there is a car share vehicle located within one block of the ADU.

Definitions in the Redlands Municipal Code:

  • Covered parking spaces: not less than 10′0″ in width and 20′0″ in length – see RMC 18.164.110(A)
  • Uncovered parking spaces: not less than 9′0″ in width and 19′0″ in length – see RMC 18.164.110(B)
  • Access to street – see RMC 18.164.120

Bedrooms:  No limit (minimum or maximum) on the number of bedrooms of an ADU. 

Kitchen & Bathroom:

ADUs (attached and detached) must have their own independent living facilities, which is to include a small kitchen or cooking area as well as lavatory facilities.

Junior ADUs are not required to have their own separate kitchen and lavatory facilities within the Junior ADU, but they must have interior access to the portions of the single-family residence that do provide the kitchen and bathroom facilities.

Type of Approval:

Ministerial approval of ADUs within a residential or mixed-use zone (i.e., building permit only).
Contact the One Stop Permit Center for application filing requirements and application fee information. 


ADUs (attached and detached): The updates to State ADU law removed the owner-occupancy allowance for newly created ADUs effective January 1, 2020. The new owner-occupancy exclusion is set to expire on December 31, 2024. Local agencies may not retroactively require owner occupancy for ADUs permitted between January 1, 2020, and December 31, 2024.

Junior ADUs: There are owner-occupancy requirements for Junior ADUs. The owner must reside in either the remaining portion of the primary residence, or in the newly created Junior ADU.

Home Owner’s Association:

Can a local Homeowners Association (HOA) prohibit the construction of an ADU or Junior ADU?

No. Assembly Bill 670 (2019) and AB 3182 (2020) amended Section 4751, 4740, and 4741 of the Civil Code to preclude common interest developments from prohibiting or unreasonably restricting the construction or use, including the renting or leasing of, an ADU on a lot zoned for single-family residential use. Covenants, conditions, and restrictions (CC&Rs) that either effectively prohibit or unreasonably restrict the construction or use of an ADU or Junior ADU on such lots are void and unenforceable or may be liable for actual damages and payment of a civil penalty. Applicants who encounter issues with creating ADUs or Junior ADUs within CC&Rs are encouraged to reach out to the California Department of Housing & Community Development for additional guidance.

Steps to building an ADU

1. Planning 

  • Homework and gather information (available on this webpage)
  • Prepare a preliminary Site Plan to verify feasibility
  • Early consultation with city staff (Planning, Building, and Engineering staff at the One Stop Permit Center)
  • Assemble your project team
  • Architect or qualified consultant prepares initial design
  • Review initial design with city staff
  • Plan refinement

2. Design

  • Construction plans prepared by architect or qualified consultant
  • Comply with applicable provisions of California Building Code
  • Comply with applicable provisions of California ADU law (see Accessory Dwelling Unit Handbook)

3. Permitting

  • Application for a building permit
  • Plan review by city staff
  • Corrections or comments on plans
  • Re-submit plans for further review, if required
  • Pay any applicable fees
  • Permit approval and issuance

4. Construction

  • You or your contractor begins work
  • Obtain necessary inspections as construction progresses
  • Obtain final inspections and sign-off

5. Move-in

Make a Site Plan

You can make a preliminary Site Plan yourself by using the City’s mapping tools available online. A preliminary Site Plan can help you explore the feasibility of building an ADU. A few clicks listed below will help you create and print a Site Plan in just a couple of minutes:

1) Go to the City’s online Zoning Map (click here)

2) On the toolbar at the top of the map, click on “Layers” and un-check Zoning.
    On the toolbar at the top of the map, click on “Basemap” and select Imagery Hybrid.

3) Find your location on the map, and scroll in for a close-up aerial photo of your property (use the scroll wheel on your mouse, or use the “+” symbol at the upper left side on the map to zoom).

For best results, make sure your property occupies most of the map window (this will ensure your Site Plan is clear and legible when you print it in the next step).

4) On the toolbar at the top of the map, click on the “Print” arrow (V) and select Landscape (PDF). 

5) The “Printout” button will appear in a few seconds, click on Printout and then a new tab will open with the aerial photo. Make sure your property occupies most of the page, and also showing the adjacent streets and sidewalks (i.e., property lines). At the upper right corner of the toolbar, select the Download button and save the document to your desktop.

Open the document from your desktop, and you can then edit the document electronically and use drawing tools (if you have PDF, Photoshop, or similar software) prior to printing. You can also print the page and draw on it. This will become your preliminary Site Plan.  

Measurement Tool: There is a measurement tool available on the Zoning Map that allows you to verify dimensions for the width of walkways, driveways, yards and setbacks, etc.  On the toolbar at the top of the map, click on the ”Measure” button and select the middle ruler symbol for ‘Distance’. Then select Feet on the drop-down list next to the ruler symbols.

State law has development standards for yards and setbacks specifically for ADUs (which are not listed in the City’s Zoning Code in RMC Title 18). The standards are different for detached ADUs, attached ADUs, and Junior ADUs. Please refer to the Accessory Dwelling Unit Handbook for further information, and check with a city planner at the One Stop Permit Center should you have any questions. 

How To Measure: Use your mouse and cursor to measure dimensions in feet. The first click of your mouse will start the measurement, and then a double-click will end the measurement. To do another measurement, just just click once again on your mouse and then double-click to end the measurement. You can then draw or write these measurements to provide the required information. 

Property Lines: A quick and easy way to verify your property lines and dimensions is to obtain a free Assessor’s Parcel Map from the County Assessor’s Property Information Management System website (click here). Click on the ‘Parcel Inquiry’ tab and  then enter your property’s Assessor Parcel Number (APN). Then select ‘View ASSR Parcel Map’ tab on the toolbar.

Additional Information 

The following links and documents are provided for informational purposes only. 

“Accessory Dwelling Unit Handbook” (click here) from the California Dept. of Housing & Community Development

For additional guidance, ADU Handbooks, or possible ADU floor plans for public use, please go to the California HCD website:

Discover the potential for an ADU on your property – ADU possibilities on your lot (click here)

“The ABCs of ADUs: A guide to Accessory Dwelling Units and how they expand housing options for people of all ages” by AARP

ADU Educational Workshops

ADU Finance Guide for Homeowners

American Institute of Architects, California – ADU Resource Center

ADU Professionals