Thinking about adding a backyard cottage in Menlo Park? With recent state and city updates, building an accessory dwelling unit is more straightforward than it used to be. Whether you want space for multi‑generational living, stable rental income, or a stronger resale story, you deserve a clear plan. This guide lays out what you can build, size and setback rules, parking, permits, costs, utilities, and the exact steps to get started. Let’s dive in.
What you can build on a single‑family lot
ADU and JADU types and count
You can typically add one ADU and one JADU on a single‑family lot, for a total of up to three homes including the main house, subject to Menlo Park’s standards. The city’s ADU ordinance in Chapter 16.79 is your primary rulebook for sizes, setbacks, parking, and process. Review the code before you design to confirm your site’s specifics.
- Review the city’s single‑family ADU standards and diagrams on the Menlo Park ADU page for a quick overview of what fits your lot. Menlo Park single‑family ADU page
- For the full legal standards, consult Chapter 16.79, Accessory Dwelling Units. Menlo Park Municipal Code 16.79
Size, height, and setbacks at a glance
- Attached or interior ADUs: minimum 150 sq ft; maximum 1,000 sq ft or 50 percent of the existing home (whichever is greater). Height and setbacks generally follow the primary home. Daylight plane rules apply. See the city’s ADU page for details.
- Detached ADUs up to 800 sq ft: maximum height 16 ft, side and rear setbacks 4 ft, and front setback consistent with the main home. These ADUs can exceed lot coverage and FAR by up to 800 sq ft.
- Detached ADUs 801–1,000 sq ft: expect a 10‑ft rear setback, up to 17‑ft height, and daylight plane limits. Converting an existing accessory structure can allow original setbacks in some cases. See the city’s ADU page for specifics.
Parking rules simplified
Many ADUs require one on‑site space, but there are several exemptions. No parking is required if the ADU is within one‑half mile of public transit, is internal to the primary dwelling, is in a historic district, is within one block of a car‑share, or if on‑street permit rules restrict parking. If you convert a garage, you do not have to replace parking for the main home. See the ordinance’s parking section for the full list. Menlo Park Municipal Code 16.79
Junior ADUs (JADUs)
A JADU is up to 500 sq ft, entirely within the main home, with its own exterior access and kitchenette. JADUs require an owner to live on site and include a deed restriction. No parking is required for a JADU. See Chapter 16.79 for the JADU standards. Menlo Park Municipal Code 16.79
Permits and approvals in Menlo Park
Ministerial review and timing
ADUs are reviewed ministerially, which means your application is approved if it meets objective standards. Conversions tend to move fastest, while new detached ADUs commonly run 12 to 24 months from feasibility through construction, depending on design, utilities, and inspections. For planning ranges and budgeting tools, use the county resource center. San Mateo County ADU Resource Center
Preapproved ADU plans (APA)
Menlo Park now offers a preapproved ADU plan program. You can choose a plan that has been vetted by the city to shorten plan review. You still submit a site‑specific building permit, but applications using a preapproved plan are prioritized. Start by reviewing the city’s APA page to see how the program works. Menlo Park Preapproved ADUs
Fees and impact fees
The city exempts ADUs under 750 sq ft from certain impact fees. Plan check, inspections, and utility fees can still apply, and school district fees may be required. Confirm your project’s fees with the city and the local school district early. See the city’s general ADU requirements for fee guidance and rental rules. General ADU requirements
Utilities and fire coordination
Water and meters
Menlo Park has multiple water providers by address. Some ADUs need a new or larger meter and backflow device, especially if sprinklers are required. Identify your provider and coordinate capacity and meter rules before finalizing plans. Menlo Park Water Providers
Sewer and laterals
Most of Menlo Park is served by West Bay Sanitary District. ADUs may need a new or upgraded lateral, cleanouts, or capacity check. Contact the district to confirm requirements and permits. Sanitary sewer information
Electric, gas, and prewiring
PG&E handles electricity and gas, and trenching or panel upgrades often add time. Menlo Park provides building guidance and prewiring notes that apply to new permits. Coordinate with your utilities and the Building Division early. Building Division
Fire access and sprinklers
The Menlo Park Fire Protection District reviews ADUs for access, hydrants, and possible sprinkler triggers. Many ADUs do not require retrofitting sprinklers in the main home, but site conditions vary. Plan a check‑in with the fire district during early design.
Costs, financing, and schedule
Typical cost ranges
ADU costs vary with size, sitework, and finishes. County guidance suggests planning around 450 to 600 dollars per square foot for new detached ADUs, with conversions often lower. Add soft costs for design, engineering, permits, utilities, and contingency. Use the county’s cost tools to refine your budget. San Mateo County ADU Resource Center
Timeline expectations
- Conversions: design and permits can be measured in months, with construction often finishing in several more months if structural work is limited.
- New detached builds: common total timelines are 12 to 24 months from feasibility through inspections. Using a city preapproved plan can shorten review, especially if your site is straightforward.
State law updates that help
Faster approvals with preapproved plans
California now requires cities to run ADU preapproval programs and to accelerate review for detached ADUs that use a preapproved plan. Menlo Park’s program aligns with this direction, which can shorten your review window if your site complies with standards. Learn more about the statewide changes. Preapproved plan context
Owner occupancy and rentals
State law prohibits cities from requiring owner occupancy for ADUs, while JADUs still require an owner to live on site. Menlo Park also applies a minimum 30‑day rental term for ADUs permitted after January 1, 2020. Review state guidance to understand the framework, then confirm local rules with the city. California HCD ADU guidance
A simple step‑by‑step game plan
- Confirm zoning and utilities. Identify your water and sewer providers and check any special overlays like historic areas or heritage trees. Water providers | Sanitary sewer
- Choose your ADU type. Use the city’s single‑family ADU page and the municipal code to match size, height, and setbacks to your lot. Single‑family ADUs | Code 16.79
- Explore preapproved plans. Ask if a preapproved plan fits your goals to reduce plan review time. Preapproved ADUs
- Budget and financing. Use county tools to estimate costs and consider grants or assistance programs highlighted by the county and state. ADU cost tools | HCD guidance
- Coordinate early with fire and utilities. Verify fire access, hydrants, sprinkler triggers, and any meter or lateral upgrades. Building Division
- Prepare your permit package. Include site plan, elevations, utility notes, and any required letters from outside agencies as directed by the city’s checklists.
- Bid and schedule. Get two to three local bids, confirm lead times, and sequence inspections and utility work to avoid delays.
How this supports your sale or long‑term plan
An ADU can increase flexibility, add rental income, or strengthen your home’s market position. If you plan to sell, presenting a clear ADU path can widen your buyer pool and support your pricing story. If you plan to hold, understanding rental terms and maintenance needs helps you forecast returns.
As a Mid‑Peninsula team, we regularly help homeowners evaluate how an ADU could impact value, timing, and future plans. If you decide to sell, we pair boutique strategy with Compass tools like Concierge, Coming Soon, and bridge financing to smooth the process and maximize your outcome. If you plan to keep the home, we can connect you with local resources and help you position the property for future flexibility.
Ready to map your options? Reach out to Marylene Notarianni for a local, data‑informed conversation about ADUs and your next step in Menlo Park.
FAQs
What is the maximum ADU size on a Menlo Park single‑family lot?
- Attached or interior ADUs can be up to 1,000 sq ft or 50 percent of the existing home, whichever is greater; detached ADUs are commonly 800 to 1,000 sq ft depending on setbacks, height, and daylight plane rules.
When is parking required for a Menlo Park ADU?
- Many ADUs need one on‑site space, but no parking is required if you meet exemptions like being within one‑half mile of transit, converting interior space, or converting a garage.
Can I rent a Menlo Park ADU short‑term?
- Menlo Park applies a minimum 30‑day rental term for ADUs permitted after January 1, 2020; vacation‑style short‑term rentals are restricted.
Will my property taxes increase if I add an ADU?
- The County Assessor handles assessments and receives permit info from the city; expect the new construction portion to be assessed while the original base value remains under Proposition 13.
Can my HOA stop me from building an ADU in Menlo Park?
- State law limits HOA bans on ADUs; HOAs can enforce reasonable design standards that do not effectively prohibit construction, so review your CC&Rs and consult the city early.
Do preapproved ADU plans guarantee faster approval in Menlo Park?
- Preapproved plans are designed to shorten plan review, and state guidance supports faster timelines, but you still need a complete, site‑specific permit and agency sign‑offs to keep things moving.
