Building an ADU in Menlo Park, California

What you can build in Menlo Park

Menlo Park's ADU rules are in Chapter 16.79 of the zoning code. The City Council adopted a new version, Ordinance 1129, on June 9, 2026, and the city says it took effect July 10, 2026. The city also says California's housing department (HCD) told it on June 15, 2026 that the ordinance "is in substantial compliance with State ADU law." You can read it on the city's ADU Ordinance update page.

ADUs are a permitted use in all zoning districts that allow single-family, multifamily or mixed-use homes. Junior ADUs (JADUs) are allowed in all single-family zones. The ordinance sorts ADUs into two groups:

• State-mandated units ("66323 Units"): On a lot with a single-family home you can have up to three: one internal (conversion) ADU, one JADU, and one new detached ADU of up to 800 sq ft. These need to meet only the limited standards set by state law.
• Locally regulated units ("66314 Units"): ADUs that don't fit the state-mandated types, such as an attached addition or a bigger detached ADU. Only one is allowed per lot, and it must meet the city's local standards (see below).

On a lot with an apartment building, you can convert non-living space such as storage rooms, attics, basements or garages into at least one ADU, up to 25% of the existing units. You can also add up to eight detached ADUs on a lot with an existing multifamily building, but no more than the number of existing units, or two detached ADUs with a proposed multifamily building.

ADUs are approved ministerially, meaning staff review without a public hearing. Projects that need a use permit to modify the standards must finish that discretionary review first. For the statewide rules, see our California ADU guide. [1][2][3]

Size, height and setbacks

State-mandated detached ADU: up to 800 sq ft of interior livable space, at least 4 ft from the side and rear lot lines. Height is 16 ft, or 18 ft within a half-mile walk of a major transit stop or high-quality transit corridor, plus 2 more feet if the roof pitch matches the main house.

Locally regulated ADUs (Table 16.79.070(1)):

• Size: at least 150 sq ft. Up to 850 sq ft with one bedroom or less, or 1,000 sq ft with more than one bedroom. An internal ADU over 500 sq ft can be up to 1,000 sq ft; at 500 sq ft or less it counts as a JADU.
• Attached ADUs: also limited to 50% of the existing home's interior livable space.
• Accessible bonus: an extra 100 sq ft if the ADU meets the California Building Code's accessibility requirements and has an accessible path from parking or the street.
• Height: attached ADUs 25 ft or the zone's height limit, whichever is lower, and subject to the daylight plane rules in Chapter 16.67. Detached ADUs 16 ft, or 18 ft near a major transit stop with 2 more feet for a matching roof pitch.
• Setbacks: 4 ft side and rear. The front setback follows the zone, but must give way if needed to fit an 800 sq ft ADU with 4-ft side and rear setbacks. Eaves may extend 18 inches into side and rear setbacks.

Guaranteed allowance: floor area limits, floor area ratio, building coverage, open space and parking rules can't block one locally regulated ADU of at least 800 sq ft with 4-ft side and rear setbacks. If you use this allowance, the main house's building permit must get its final inspection before the ADU's.

Conversions: no setback is required for existing living area or an existing accessory building converted to an ADU, or for a structure rebuilt in the same place and size. Additions beyond the footprint (up to 150 sq ft for getting in and out) must meet the 4-ft side and rear setbacks. [1]

Parking

Menlo Park requires no parking for ADUs or JADUs. When a garage, carport or covered parking structure is torn down or converted to build an ADU, "those off-street parking spaces need not be replaced." If you want to keep parking, you can provide it as tandem parking on a driveway. [1]

Fees

ADU applications must be "accompanied by the appropriate fee," and an ADU is permitted through a building permit. Building and planning fees come from the city's Master Fee Schedule, which the City Council approved on April 28, 2026. It sets building plan check and permit fees by occupancy type and size, and passes credit and debit card processing fees through to the payer.

Impact fees: Under state law, no city, special district or water company may charge impact fees on an ADU with 750 sq ft or less of interior livable space, or a JADU of 500 sq ft or less. Above those sizes, impact fees must be in proportion to the unit's size compared with the main house. Menlo Park's fee schedule lists a "Building Construction Street Impact Fee" of 0.58% of project valuation on construction projects over $10,000 (residential alterations and repairs excluded). The schedule doesn't say how this applies to small ADUs, so ask the Building Division before you budget for it.

School fees: State law lets school districts charge fees on ADUs larger than 500 sq ft of interior livable space.

Utilities: An ADU or JADU created inside existing or proposed space under state law (Gov. Code 66323(a)(1)) can't be required to install a new or separate utility connection or pay a related connection fee or capacity charge, unless it is built with a new single-family home or approved for separate sale. An ADU built with a new home needs its own connection, and it may be charged a connection fee or capacity charge in proportion to its size or plumbing fixtures. For other ADUs, ask the Building Division and your water and sewer providers what applies. You must also submit a letter from the sanitary district confirming there is enough sewer capacity for the ADU.

For budgeting help, see our ADU cost guide and ADU financing guide. [1][4][5][6]

How long it takes

Since January 1, 2026, Menlo Park reviews ADU applications in two steps:

• Completeness: within 15 business days (days City Hall is open), the city tells you in writing whether your application is complete. Each resubmittal starts a new 15-business-day review. If the city misses this deadline, the application is deemed complete.
• Decision: once complete, staff must approve or deny the application within 60 calendar days on a lot with an existing home. If no decision is made in that time, the application is deemed approved. If it is denied, you can resubmit and start a new 60-day cycle. If you apply for an ADU together with a new main house, the city may act on both at the same time.

You can appeal a completeness decision or a denial in writing to the Planning Commission within 15 calendar days. The commission must decide within 60 business days. See our ADU permit process guide for the general steps. [1][3][7]

Junior ADUs and garage conversions

A JADU must be between 150 and 500 sq ft of interior livable space and sit entirely inside a single-family home. It may add up to 150 sq ft beyond the house's walls, only for getting in and out. It needs a separate entrance and a permanent efficiency kitchen. A JADU without its own bathroom must have both a separate entrance and an interior door into the main living area. No parking is required.

Owner occupancy: only when the JADU shares a bathroom with the house. In that case the owner must live in the house or the JADU. The owner must record a deed restriction that bars selling the JADU separately from the house. A JADU may be rented, but not for less than 30 consecutive days.

Garage conversions: a garage or other accessory building can become an internal ADU, with up to 150 sq ft added for getting in and out. If the existing building wouldn't otherwise meet the location or height rules for an ADU, the city's checklist asks you to show it was legally permitted, for example with a city building permit or a San Mateo County property assessment record. See our junior ADU guide and garage conversion guide. [1][7]

Renting it out

You may rent an ADU separately from the main house, but "not for a period of less than thirty consecutive days." State-mandated ADUs and JADUs carry the same 30-day minimum, so short-term rentals are out. An ADU can't be sold separately from the main house unless the conditions in state law (Gov. Code 66341) are met; HCD calls this "a narrow exception" for homes built by a qualified nonprofit corporation. [1][6]

Legalizing an unpermitted ADU

If your ADU or JADU was built without permits before January 31, 2023, the city may not deny a permit to legalize it because of building standard violations or because it doesn't meet the ADU chapter, unless the Community Development Director finds a fix is needed to protect health and safety. You won't be required to pay impact fees or connection or capacity charges, except in limited cases where utility work is needed for safety. Before applying, you may get a confidential code inspection from a licensed contractor. Proof of the build date can include utility records, assessor records, aerial images, dated photos, contractor invoices, rental agreements or insurance records. [1]

SB 9 lots

SB 9 lets you build two homes on a single-family lot and split it once. In Menlo Park it applies in the R-E-S, R-E, R-1-S, R-1-S (FG), R-1-U and R-1-U (LM) zones. On a lot that is not split, the city says ADU law can be combined with SB 9 for up to four units: two main homes and two ADUs. The ADU ordinance doesn't allow ADUs or JADUs on a lot that has both an approved urban lot split and an approved two-unit development. Each lot from an urban lot split must be at least 1,200 sq ft, and the applicant must sign an affidavit to live in one unit for at least three years. The city is updating its SB 9 rules; see the SB 9 Projects page and our SB 9 guide. [1][8]

Permit steps in Menlo Park

1. Talk to the city first

   Staff recommend coming to the public information counter to discuss ADU rules with Planning, Building and Engineering before you apply. Planning is at 650-330-6702, and you can make an appointment online. [3][9][10]

2. Design to Chapter 16.79

   Have plans drawn that show compliance with the ADU chapter and your zone: site plan, floor and roof plans, elevations, sections, floor area and building coverage diagrams, and a boundary and topographic survey. [7]

3. Gather engineering and tree documents

   ADUs over 500 sq ft need grading, drainage and improvement plans. Add an impervious area worksheet, plus flood zone or creek documents and an arborist report if they apply. [7]

4. Submit the building permit application

   Submit the building permit application with the city's ADU Completeness Checklist, initialing each item, and pay the application fee. [1][3][7]

5. Record a JADU deed restriction

   For a junior ADU, record the deed restriction barring separate sale and limiting the JADU's size and features. [1][7]

6. Completeness review and decision

   The city answers on completeness within 15 business days, then approves or denies within 60 calendar days. Track your permit on the city's Accela portal. [1][3][11]

7. Build and pass inspections

   Schedule inspections online or by calling 650-330-6767. [11]

Pre-approved and sample plans

• Menlo Park Preapproved ADUs

  City preapproval for designers' ADU plans; no approved plans were listed as of October 2026. [12][13]

Who to call

• Menlo Park Planning Division

  ADU zoning rules and the ADU ordinance

  650-330-6702

  701 Laurel St., Menlo Park, CA 94025

  [7][9]

• Menlo Park Building Division

  Building permits and general questions

  650-330-6704

  [11]

• Menlo Park Building Inspections

  Inspection questions and scheduling

  650-330-6767

  [11]

Questions people ask