Hidden Hills

Accessory Dwelling Unit (ADU’s)

Preapproved ADU Plan Submittal Process

What is an Accessory Dwelling Unit?

An accessory dwelling unit, defined in Government Code Section 65852.2 refers to an attached or a detached residential dwelling unit that provides complete independent living facilities for one or more persons and is located on a lot with a proposed or existing primary residence.

For more information and resources on ADUs, visit the Department of Housing and Community Development’s website:
https://www.hcd.ca.gov/policy-and-research/accessory-dwelling-units

Overview

Assembly Bill (AB) 1332 (Government Code Section 65852.27) requires local agencies to develop a program and process to preapprove architectural and design plans for accessory dwelling units (ADUs) by January 1, 2025. Major components include:

  • Develop a preapproval program for ADUs,
  • Streamlined 30-day approval for preapproved plans.

Streamlined 30-day Approval

AB 1332 requires a local agency to approve or deny an application for a detached ADU ministerially within 30 days from the date the local agency receives a completed application* by either of the following:

  1. a plan for an ADU that has been preapproved by the local agency within the current triennial California Building Standards Code rulemaking cycle pursuant to the standards outlined above, or
  2. a plan that is identical to a plan used in an application for a detached ADU approved by the local agency within the current triennial California Building Standards Code rulemaking cycle.

*Completed application includes HHCA Architectural Committee approval. The 30-day timeframe begins upon submittal of the completed application to the City.

ADU PREAPPROVED PLAN REVIEW PROCESS

This guide has been developed to assist architects and designers in preparation of a submittal for ADU preapproved plans. Please follow the steps outlined below.

Advisory. These are not the steps for a building permit submittal. Homeowners must obtain a building permit from Building & Safety for the construction of a preapproved ADU. For more information on how to apply for a building permit, please review the “For Homeowners” section below.

FOR DESIGNERS

Step 1: Determine Eligibility
Preapproved ADU Plan submittals must meet the following criteria:

  1. Detached, single-unit ADUs only.
  2. New construction (not conversions).
  3. Minimum unit size of 250 sf.
  4. Maximum unit size of 800 square feet.
  5. Maximum one-story and height up to 16 feet (measured from grade to roof ridge).

Step 2: Submit for Design Review Preapproval
Prepare and submit conceptual architectural plans for Hidden Hills Community Association (HHCA) Architectural Committee preapproval. The plans must include:

  1. Title sheet with placeholders for:
    a. Project data
    b. Vicinity map
    c. Scope of work
    d. Sheet index
    e. Applicable codes
  2. Placeholder site plan sheet
  3. Placeholder sheet for existing building and site photos showing all sides of the existing main residence
  4. 3-D colored rendering
  5. Elevations showing:
    a. Building materials (exterior finishes, colors, roofing materials)
    b. Window specifications (dimensions, operation, and include a window section with dimensions and muntin specifications)
    c. Plate heights, roof pitch
    d. Building height
  6. Up to two building sections
  7. Floor plan
  8. Materials options (if proposed)

Step 3: Architectural Committee Review
At the HHCA Architectural Committee meeting, the Committee may approve, conditionally approve, or deny the designs. If your design is denied, you may revise and resubmit for preapproval.

Step 4: Submit for Building and Safety Review
After your design has aesthetic preapproval, you may submit detailed drawings for Building & Safety review. Pay the appropriate fee and, after payment of fees, the plans will be reviewed by the City’s Building & Safety Division for compliance with all codes and requirements. There may be more than one round of plan check review if corrections are necessary.

Step 5: Final Decision
At the end of both the HHCA Architectural Committee’s and Building & Safety’s review periods, you will be notified of the City’s decision to preapprove your plans. If your design is preapproved, the plans will be posted on this webpage along with your contact information for use by future potential clients. The City will remove a preapproved ADU plan from the website within 30 days of receiving a request for removal from the applicant. You will still retain your copyright to the preapproved design, so any homeowner who wishes to use the design must contract with you to do so.

Advisory. Designers may need to update plans if the City adopts new building or zoning codes which affect your ADU plan. The City will notify you when such changes take place and let you know how updated plans can be submitted.

FOR HOMEOWNERS

The City is launching the Preapproved ADU Program for homeowners to use and designers to apply to, starting in January 2025. Homeowners can then reach out to the designer of the plan they select and work with them throughout the process. Browse the City’s list below – New plans coming soon!

 How to Apply for a Building Permit

Preapproval does not mean that the designs already have their building permits, but rather that elements of the permitting process for your ADU will already be addressed upon application submittal. Preapproved plans are around 70-80% complete but you will still be required to provide site-specific information. This guide has been developed to assist you in the preparation of your building permit submittal for your Preapproved ADU. Please follow the steps outlined below.

  1. Contract with the designer responsible for the preapproved ADU plan set.
  2. Submit additional site-specific plans, studies, and engineering, as applicable.
  3. Obtain HHCA Architectural Review Committee approval of the preapproved ADU.
  4. Obtain a building permit from Building & Safety for the construction of a preapproved ADU.

The full list of submittal requirements and logistics for a building permit are included below.

Permit and Plan Review Application
Permit Center

PREAPPROVED ADU PLANS

At this time, no plans have been preapproved by the City of Hidden Hills. Refer back to this webpage for updates or reach out to the City’s Building and Safety/Planning webpage with any questions.

Disclaimer. Please note that the City of Hidden Hills has reviewed the above accessory dwelling unit plans and found them in conformance with all applicable zoning and building code requirements. Please note that preapproval by the City of Hidden Hills of ADU plans does not constitute an endorsement or recommendation of any specific designer, contractor, or other design professional by the City.