Accessory dwelling units
An accessory dwelling unit (ADU) is a dwelling unit on a residential lot which provides complete independent living facilities for one or more persons, and includes permanent provisions for living, sleeping, eating, cooking, and sanitation independent of the main dwelling(s). ADUs are sometimes called an “in-law unit” or a secondary dwelling unit. ADUs, and junior ADUs, or JADUs, have been the focus of recent State legislation, as they can provide needed housing without materially changing the visual character of a neighborhood. The Planning and Building Divisions are committed to making the ADU review process as predictable and streamlined as possible for our customers. Please review the information below for details regarding the ADU requirements by building type, the process for new proposals and links to the related handouts and State legislation. Links are also available through the related documents section to the right of your screen if viewing through a web browser.
Requirements and guidelines
The table below contains general requirements related to ADUs. For specifics regarding setbacks, allowable heights, sizes and other development regulations for an ADU on a lot with a single-family residence or existing multi-family building please review the appropriate webpage to the left and the materials in table 2, below. Please click the zoning layer through the interactive GIS map to look up the zoning for a particular parcel. The map layer for zoning may not be activated by default, but can be applied after following the preceding link. Specific requirements for development vary between single-family or multifamily residential zoning districts according to the zoning of the parcel of interest.
|General ADU requirements
|Minimum lot size
|Minimum unit size
||Not permitted, unless associated with an affordable housing nonprofit per AB587
|Aesthetic similarity to primary dwelling
||Must provide exterior access separate from the primary dwelling for all ADU/JADUs.
|Sanitation facilities (restroom)
||Must be independent for ADU, JADU can be shared with primary dwelling
|Cooking facilities (kitchen)
||Must be independent and must include the following:
- Permanent range
||None for ADUs permitted between Jan. 1, 2020, and Jan. 1, 2025, for a JADU the owner is required to reside in either the primary dwelling unit or the JADU.
||30 days, minimum, for ADUs permitted after Jan. 1, 2020
||No impact fees for ADU < 750 sf
ADU applications that meet all zoning ordinance requirements may be reviewed and approved by staff. Before starting such an application, staff recommends coming in to the counter (see hours at top right of this page) to discuss the ADU regulations. Project plans (including a site plan, floor plans, floor area and building coverage diagrams(PDF, 470KB), and elevations) are required with ADU applications.
Following the Planning Division's recommended preliminary review, applicants who are proposing fully-compliant ADUs will coordinate with the Building Division to confirm the items required for submittal of a building permit application. In general, the following guidelines are applicable to ADU building permits, depending on the specific proposal:
Please note that new ADUs require a number of standard fees, including (for ADUs 750 square feet and greater) proportional impact fees. One such impact fee are the school fees charged by the local school district. As a hypothetical example, if the primary dwelling unit is 2,000 square feet and the ADU is 1,000 square feet, and the school fee was $3.79/square foot the ADU would be responsible for $3,790 in school fees. Please consult the Building Division to confirm the school district for your property, the fees vary by district. The Building Division can also provide detailed fee quotes before an application.
ADU applications that do not meet all zoning ordinance requirements may be reviewed and acted on with a use permit by the Planning Commission (with the exception of the density and subdivision requirements, which may not be modified). Please contact the Planning Division if you are considering any such application for discretionary review.
Background and additional resources
A number of state laws regarding accessory dwelling units became effective Jan. 1, 2020. The following California Government Code sections may be referenced, however please defer to the information above for Menlo Park specific regulations:
Which properties qualify as a lot with a single-family residence?
Properties developed with one standalone single-family dwelling, one standalone single-family dwelling and ADUs, or lots developed with no more than two standalone single-family dwelling condos shall follow the requirements for existing developments under the SF ADU requirement handout and section 16.79.050.
Which properties qualify as a lot with an existing multi family building?
Properties developed with apartments, townhouses with shared walls and those developed with more than two standalone single-family dwellings on the same lot are considered multi-family buildings. These properties follow the requirements outlined in the MF ADU webpage and section 16.79.090.
Do ADUs count toward floor area and building coverage limits?
Yes. However, for ADUs proposed with a single-family residence, or on a lot with an existing single-family residence, a new ADU that is 800 square feet or smaller in size may exceed the floor area limit and building coverage limits by up to 800 square feet if built after or concurrently with the primary dwelling unit. Additions to the area of existing ADUs may not exceed the limits for the lot that they were built on, nor can additions to the primary dwelling unrelated to the ADU exceed the limits. Please review the SF ADU webpage for additional information. New ADUs on properties with existing multi-family buildings may also exceed the floor area ratio by the gross floor area of the ADU(s). Please review the MF ADU webpage for additional information. Please review the Zoning Ordinance for the definitions of floor area, building coverage and gross floor area.
Is an ADU an accessory building?
An ADU is not considered an accessory building, and therefore will not be regulated as one. This means an ADU will not count toward the maximum allowable area for accessory buildings and structures, and the proposal will not be required to maintain 10 feet of separation between the ADU and the primary dwelling. For more details about ADU regulations, please refer to Chapter 16.79 (“Accessory dwelling units”) of the Zoning Ordinance. For more details about accessory building regulations, please refer to Chapter 16.68.030 (“Accessory buildings and accessory structures”) of the Zoning Ordinance and the accessory buildings and structures handout(PDF, 156KB) .
Can I convert an existing accessory building into an ADU?
An accessory building (including detached garages/carports) may be converted into an ADU so long as the following criteria are met:
- A building permit or other supporting documentation is provided to show the structure was legally built;
- The building can be upgraded to meet the Building Code requirements for a dwelling unit; and
- The accessory building complies with the development regulations for an ADU, with the exception of:
- Minimum yards;
- Daylight plane; and
All or any portion of an accessory building that meets the above eligibility criteria may be demolished and reconstructed to meet building code requirements based on the change of occupancy at the time of conversion. The ADU that replaces the accessory building may retain the setbacks and the footprint of the legally constructed accessory building. If the proposed ADU exceeds the permitted unit size of 1,000 square feet, a use permit may be requested to deviate from this standard.
Can I convert my attached garage/carport into an ADU?
The garage/carport of an existing residence may be converted into an ADU provided the ADU maximum unit size requirements are met. While not required, providing replacement off-street parking for the existing residence is strongly recommended (see parking question below). The replacement parking can be allowed in any configuration on the same lot, including covered spaces, uncovered spaces, tandem spaces, or mechanical parking lifts. Uncovered replacement parking must meet the dimensional requirements of the Parking Stalls and Driveway Design Guidelines(PDF, 383KB) , and may not extend onto the public right-of-way.
Do I need to provide parking for my ADU?
Section 16.79.080 contains the parking requirements for ADUs. In most cases, one off-street parking space is required. However, no parking is required for the ADU if the ADU is:
- Located within ½ mile walking distance of public transit;
- Located within an architecturally and historically significant historic district;
- An interior ADU;
- Not eligible for on-street parking permits, but on-street permits are available; or
- Within one block of a car share vehicle.
Please note, the City does not currently include historic districts and residents in single-family homes may only purchase temporary permits for on-street overnight parking, so exceptions b) and d) are not currently applicable. If developing an ADU or converting an accessory structure into an ADU results in inadequate parking at your property for the additional people occupying the property, you will not be exempt from the overnight parking prohibition nor other parking restrictions and may need to limit the number of vehicles at the property.
Can I rent out my ADU?
For ADUs constructed after January 1, 2020, a minimum of 30-day lease term is required to rent out an ADU. There is no minimum lease term for a JADU. For a JADU constructed after January 1, 2020 and ADUs constructed after January 1, 2025 the answer is yes, so long as the primary dwelling unit or ADU is occupied by the property owner. For ADUs constructed before January 1, 2020, JADUs, and ADUs constructed after January 1, 2025 both the main dwelling unit and the ADU cannot be rented or used as a dwelling by persons other than the property owner unless the property owner has completed the non-tenancy status registration process or received a use permit. For more information about tenancy status related to properties with ADUs, please see section 16.79.100(1) of the Zoning Ordinance. As part of the building permit application for a new JADU and new ADUs after January 1, 2025, the property owner shall be required to provide a signed tenancy acknowledgement form(PDF, 58KB) .
Is there a daylight plane requirement for ADUs?
There is no daylight plane requirement for ADUs 800 square feet and smaller, or for those in zoning districts without daylight plane requirements. A detached ADU that is larger than 800 square feet in area has a separate daylight plane requirement that must be met, unless a use permit is approved to deviate from this ADU standard. The daylight plane for a detached ADU is established at a line three (3) feet from the side property lines. The daylight plane begins at a horizontal line 9 feet, 6 inches above the average grade with a slope inwards at a 45 degree angle. There are no permitted intrusions into this daylight plane. The daylight plane requirement for an attached ADU is the same as the daylight plane required for the primary dwelling.
Will my property taxes increase with an ADU?
Property taxes are assessed by the County of San Mateo Assessor’s Office, not by the City of Menlo Park. For all development projects in the City, the County collects information from the City when building permits are issued to a property. Please contact the County Assessor’s Office for more information about how the information is used.
What fees are required for an ADU?
An ADU is considered a new single-family residence from a building code perspective and there are a number of plan check and technical report fees that may apply depending on site conditions in given geographic regions of the City, as well as whether the ADU is proposed as a detached, attached or interior ADU. ADUs 750 square feet or smaller in size are exempt from impact fees for the City, although school impact fees may apply. The building pre-application (BPA) record type through our online permit portal is active. Prospective applicants can create a BPA through the online services webpage and email the Permit Team with questions regarding all the fees and the process for their specific proposal. The Sequoia Union School District can be reached by phone at 650-369-1411 ext. 22203 with questions regarding school impact fees.