STATEWIDE UPDATE: New California ADU Bills SB13, AB68, AB881, AB670 have passed. These laws will create more options for building an ADU in Hillsborough in 2020. To prepare for the upcoming changes use our ADU Services to learn how these laws will effect your property!
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 08/11/19


The city government of Hillsborough will approve ADUs under California's statewide mandated regulations.
The California Building Code (CBC) 2016 is adopted with the following amendment(s): 742
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:

One ADU per lot. The lot upon which the ADU is to be located must contain a single-family residence.

AB68 & AB881 Update: Properties which convert existing space to create ADUs may be eligible for one ADU -AND- one JADU.

Types of ADUs allowed:

Attached, detached and junior ADUs are allowed.

Lot size:

Per state requirements.

AB68 & AB881 Update: Properties will not be subject to minimum lot standards by ordinance or of the applicable zoning district.

ADU size:

Detached ADUs may not exceed 1,400 square feet in floor area. Attached ADUs may not exceed 30% of the floor area of the primary dwelling (not including the garage area).

AB68 & AB881 Update: Properties will be allowed up to 850 square feet for a one bedroom or up to 1,000 square feet for a two bedroom ADU.


Setback requirements as specified in the Hillsborough Municipal Code for all residences. (Review the Development Standards information available online at

AB68 & AB881 Update: The maximum required setback for a detached new construction ADU shall be no more than 4 feet from the rear or side property lines.


Parking: ADUs with one or two bedrooms require one parking space, and ADUs with three or more bedrooms require two parking spaces in addition to those required for the primary dwelling. These parking spaces may be unenclosed and cannot be in tandem. Exceptions to the parking requirements may be granted for ADUs including two or more bedrooms.

AB68 & AB881 Update: Properties which convert an existing garage will not be subject to replacement parking requirements.

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.


The ADU may accommodate an extended family, a caregiver, or it may be rented. Either the ADU or the primary dwelling may be rented, but not both at the same time unless both are rented to the same party.

That the ADU may not be sold separately.

SB13 Update: Owner-occupancy requirements for ADUs will be voided statewide for 5 years.

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: 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.

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) 2016 is adopted with the following amendment(s): 742

Hillsborough City Planning Offices

Hillsborough Building Department

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

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

ADU Guides

ADU Services

A recent customer review:

"Hausable provided all of the information we needed to make a decision about building an ADU. Thanks for the excellent service!"

Thea in Escondido, CA

Customer since August, 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


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)

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

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.

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.

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

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