Single-family residential accessory dwelling units

Properties developed with a single-family residence may construct up to two accessory dwelling units (ADUs), one that is detached and one that is either attached, interior or junior. These ADUs may be created through the conversion of existing spaces. Any ADU that is created from existing space, either within the primary dwelling or detached accessory building, may retain the setbacks of the existing structure. The tables below outline requirements for attached, detached and junior ADUs. For full details regarding development regulations related to ADU proposals on properties developed, or proposed to be developed, with a single-family residence, please review the online Municipal Code, section 16.79.050. Please review Municipal Code section 16.79.060 b) for details regarding setbacks for conversions.

Attached and interior ADUs

An attached ADU is a unit that is constructed as a physical expansion (i.e., addition) of an existing primary dwelling unit, including a new basement underneath a primary dwelling unit. An interior ADU is a dwelling unit that is contained within the existing space of a primary dwelling unit, including within its living area, basement, or attached garage or constructed as part of a proposed primary dwelling unit. Please consult the tables below for information regarding the requirements for attached or interior ADUs.

Attached ADU requirements
Minimum unit size 150 sf
Maximum unit size
1,000 sf or 50% of the existing area of the primary dwelling, whichever is greater
Bedrooms 2 max
Minimum setback: front
Same as primary dwelling
Minimum setback: corner side
4 ft
Minimum setback: interior side
4 ft
Minimum setback: rear
4 ft
Maximum height
Same as primary dwelling
Daylight plane
Same as primary dwelling
Permitted to exceed FAR and lot coverage maximum
Yes, if ADU is 800 sf or smaller and built at the same time as, or after, the primary dwelling and other structures
Parking
One off-street parking space required for attached ADUs (OK in tandem/setback configuration). Certain sites are not required to provide parking, see 16.79.080 for details. On-street parking overnight is prohibited in single-family zoning districts. Please see the FAQs for additional information regarding the City's overnight parking prohibition.

Interior ADUs must be within existing space. Conversions of existing space to interior ADUs may maintain existing setbacks provided sufficient distance is required for compliance with fire and life safety building code requirements, per Municipal Code section 16.79.060 b).

Interior ADU requirements
Minimum unit size 150 sf
Maximum unit size 1,000 sf or 50% of the existing area of the primary dwelling, whichever is greater
Bedrooms 2 max
Parking None required for interior ADUs. On-street parking overnight is prohibited in single-family zoning districts. Please see the FAQs for additional information regarding the City's overnight parking prohibition.

Junior ADUs

A Junior accessory dwelling unit (JADU) means a dwelling unit that is no more than 500 square feet in size and contained entirely within an existing or proposed single-family dwelling. A JADU shall include cooking facility with appliances and a food preparation counter and storage cabinets that are of reasonable size in relation to the size of the JADU. A JADU may include separate sanitation facilities or may share sanitation facilities with the primary dwelling. A JADU must have exterior access separate from the primary dwelling. Please review section 16.79.070 for full details regarding regulations applicable to JADUs.

Detached ADUs

A detached ADU is a dwelling unit that is constructed as a separate structure from the primary dwelling unit, contained within the existing space of an accessory structure, or constructed as an addition to an existing or proposed accessory building. Requirements for detached ADUs vary by size for units up to 800 square feet and those between 801 square feet and the maximum size allowed, 1,000 square feet. Please consult the table below for information regarding the requirements for detached ADUs. Conversions of permitted accessory buildings to detached ADUs may maintain existing setbacks per Municipal Code section 16.79.060 b). 

ADU requirements ADUs up to 800 sf ADUs 801-1,000 sf
Minimum unit size 150 sf 150 sf
Maximum unit size 800 sf 1,000 sf
Bedrooms 2 max 2 max
Minimum setback: front same as primary dwelling same as primary dwelling
Minimum setback: corner side 4 ft same as primary dwelling
Minimum setback: interior side 4 ft same as primary dwelling
Minimum setback: rear 4 ft 10 ft
Maximum height 16 ft 17 ft
Daylight plane n/a at 3 ft setback, measure up 9.5 ft, then slop inwards at 45 degrees
Permitted to exceed FAR and lot coverage maximum Yes, if built at the same time as, or after, the primary dwelling and other structures No
Parking One off-street parking space required (OK in tandem / setback configuration). Certain sites are not required to provide parking, see 16.79.080 for details. On-street parking overnight is prohibited in single-family zoning districts. Please see the FAQs for additional information regarding the City's overnight parking prohibition.

FAQs

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 accesory 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:

  1. A building permit or other supporting documentation is provided to show the structure was legally built;
  2. The building can be upgraded to meet the Building Code requirements for a dwelling unit; and
  3. The accessory building complies with the development regulations for an ADU, with the exception of:
    1. Minimum yards;
    2. Height;
    3. Daylight plane; and
    4. Parking.

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.