Schedule ADU Consultation
(650) 730-2387 ext: 376
Schedule ADU Consultation (650) 730-2387 ext: 376

Hillsborough ADUs

Everything about building Accessory Dwelling Units in Hillsborough, CA

Research local zoning codes for ADU design
Calculate returns and costs to get financing
Estimate your project costs and timeline

Check your property to get zoning info & price quotes for ADU feasibility & design services:

I'm interested in

Hillsborough ADU Guidelines Last Updated 04/05/20

PLANNING OFFICE The city has closed all operations during the COVID-19 outbreak. More information will be posted here once it becomes available. In the meantime, we are providing services for Hillsborough properties based on recent projects and research.

The city government of Hillsborough will approve ADUs under California's statewide mandated regulations.
The California Building Code (CBC) 2019 is adopted.
Relevant state bill updates for SB13, AB68, AB881, AB670 are shown in green below.


City Hint: The city has not yet responded to requests for ADU permit volumes for the past year, but they will be provided here once response has been received.

Number of ADUs allowed:

According to state law, all single-family homes are allowed at least one ADU. Additionally, single-family properties which are owner-occupied may create one ADU and one Junior Accessort Dwelling Unit (JADU). Also, multi-family properties may now add one ADU per every four existing residential units, so long as they were legally established.

As of January 1st, 2020

Types of ADUs allowed:

Detached ADU, Attached ADU, Junior ADU are approved. Accessory Dwelling Unit (ADU)s may be new construction or converted from existing space. Junior ADUs must be converted from existing space.

Lot size:

Accessory Dwelling Unit projects on single family or multi-family residential parcels will not be subject to the minimum lot size of the underlying local zoning code or by special ordinance. ~ AB-68

As of January 1st, 2020

ADU size:

Single-family and multi-family Properties will be permitted to construct up to 850 sq.ft. for a one bedroom ADU or up to 1,000 sq.ft. for a two bedroom ADU, regardless of the underlying zoning standards of the property. A Junior Accessory Dwelling Unit up to 500 sq.ft. is permitted. The minimum size of any living unit (including ADUs and Junior Accessory Dwelling Units) is 150 sq.ft. according to Califronia Residential Code. ~ AB68 & AB881 Update

As of January 1st, 2020


The maximum required setback for a detached new construction Accessory Dwelling Unit (ADU) shall be no more than 4 ft. from the rear and side property lines. Setbacks will not be required for Accessory Dwelling Unit (ADU)s and Junior ADUs converted from existing space that was legally eastablished. Attached Accessory Dwelling Unit (ADU)s and conversions from existing space to be expanded will be required to comply with the setbacks of the underlying zone. ~ According To AB68

As of January 1st, 2020


Lots which convert an existing garage to an ADU or Junior Accessory Dwelling Unit will not be subject to replacement parking requirements. ~ AB68 & AB881 Update

As of January 1st, 2020

Fire Safety:

Per state requirements.

Shape, materials and style:

New construction/exterior changes (if any) should be designed to be compatible with the architectural style and detailing of the primary unit.


Height of the ADU will be determined by the maximum height of the underlying zone.

Design review:

For the required approval by the Planning Division, the Planning staff can approve most new ADUs administratively. If staff approval is not possible, the application will require approval by the Town’s Architecture and design review Board.

After approval from the Planning Division is secured, construction drawings may be prepared and submitted for the Building Permit application.

Number of Bedrooms:

Not specified by State Standards.


Owner-occupancy will not be required for new ADUs (conversion and new construction) built between 2020 and 2025. ~ SB13 Update

As of January 1st, 2020

Utility connections:

Local health officer approval where a private sewage disposal system is being used, if required. (State requirements)

There are no fees for the Planning Division review and there are no Building Permit fees for second units; Building Division plan-checking and other related fees do apply.

SB13 Update: As of January 1st, 2020, local impact fees for ADUs will be reduced substantially statewide.


The term “second unit” means a residential dwelling unit that provides complete independent living facilities for one or more persons and is located on the same lot as the main house (called the “primary dwelling”). The second unit includes permanent provisions for living, sleeping, eating, cooking, and sanitation.

Allowed Zones:

*** Beginning in 2020, according to state law, all residential zoning districts, including single-family and multi-family, are allowed to build Accessory Dwelling Units. ***

As of January 1st, 2020

Lot Coverage:

The second unit must be constructed within the allowable maximum permitted floor area (FAR) and lot coverage of the applicable zoning district.

Conversion of Existing Space

Conversion of existing residential space (where there is no new construction proposed):
To secure approval of the conversion of existing space, first secure Planning Office, then Building
Department approval:
1. To secure Planning approval of the second unit, submit a completed Second Unit application,
demonstrate (with photos, a site plan, etc.) there is sufficient parking on the property for both the
primary and the second unit, and complete the request for the preparation of the document (for which
there is a fee for the City Attorney’s Office) to be recorded to alert future owners of the regulations
regarding a second unit. Submit these items to the Planning Division for approval. Once evidence of
the recordation of the required document is received, Planning Division approval will be granted.
2. After securing Planning Division approval, the applicant shall obtain all necessary permits and
arrange an inspection by the Building Division. The Building Division will check for any significant
health or safety problems. If there are repairs required, the applicant will work with the Building
Division to correct them. If there are no safety or Code problems, the second unit will be approved.

SB13 Update: Amnesty program to permit unpermitted units will be administered statewide, allowing non-health and safety code violations to be deferred.

Residential Building Code:

The California Building Code (CBC) 2019 is adopted.

Hillsborough City Planning Offices

Hillsborough Building Department

1600 Floribunda Ave. Hillsborough, CA 94010 Hillsborough, CA 94010

Read Hillsborough Housing Market Update

Call/Text ADU Operator (650) 730-2387
Call Hillsborough ext: 376 |
'Text to Check' Your Property sms: "123 Main St, Hillsborough"

Are you an ADU Pro? Get featured here.

ADU Example Designs

ADU Model 480 sqft

W 24 ft L 20 ft

ADU Model 450 sqft

W 30 ft L 15 ft

Hillsborough ADU Marketplace

How can I get my ADU built?

Use our ADU Services and Marketplace to get expert assistance, permit-ready ADU designs and on-site contractor estimates on one platform.

Fast and low cost ADU design services

Search local contractors to get estimates

Featured Financing Program

ADU Financing

CA Statewide

Tailored to ADU construction.
Based on project size & appreciation.
Learn how to qualify.

Karyn Jones

Program Representative

Call Now (760) 496-5959

Read Hillsborough Housing Market Update

Featured ArticleState of CA
Featured ArticleState of CA

California Housing Revolution? 2018-02-22

Featured ArticleState of CA

Opinion: How California can solve its housing disaster 2018-02-02

ADU Guides

ADU Services

A recent customer review:

"I would recommend these services as a cost effective way to begin the serious research necessary to organize an ADU project."

Sharon in Los Angeles, CA

Customer since July, 2018

Learn about ADU Services

Estimate ADU Potential
Costs / ROI



* upon completion of ADU


* based on local average price per sqft


* estimated by location


* 30 years / 5% interest rate / 20% down payment


Size: 500 sqft


Appreciation Estimate = (Base Value: $) / (Home's Living Space: sqft) * (ADU's Living Space: sqft)

Rental Estimate = (Rent Per Sqft: $3.25) * (ADU's Living Space: sqft)

Find ADU Contractors

How can I get my ADU built?

Our ADU Services and ADU Marketplace provide the fastest and lowest cost way to get started with your ADU project.

How does it work? Get started on your project with expert assistance and without commitment using our customized ADU Property and Design Reports as your first step. Then, get on-site visits from local contractors who can provide you with guidance and estimates for your ADU project.

Our Key Advantages

Compare all the costs and services in one place to find the best fit for your needs and budget

Order ADU zoning research, permit-ready designs and contractor estimates on one platform

Get started on your timeline and your terms, without commitment

The fastest and lowest cost way to get started with your ADU project

Our ADU Process

Expert Feasibility & Zoning Research

Expert Feasibility & Zoning Research

Use our ADU Property & Design Reports as a starting point to plan your ADU project. Our experts will do the legwork with your city or county planning office and design custom ADU concepts for your property and your needs.

Get Your ADU Design Permit-Ready

Get Your ADU Design Permit-Ready

Getting your designs ready for city permitting and construction can speed up your ADU project and reduce unforseen costs later on in the process.

Find contractors to build your ADU

Find contractors to build your ADU

Use our local contractor database to get on-site visits and cost estimates to compare services for your ADU project.

Check your property to get zoning qualification & price quotes for ADU Services:

Access cost estimates, zoning analysis, design concepts and order ADU Services to get help with feasibility, design and permitting for your ADU project. Check your property to get started!

I'm interested in