Monrovia, CA Zoning and ADU Guide for Homeowners

Last updated November 13, 2026. Reviewed by the Cash Home Buyers CA team.

Monrovia updated its ADU ordinance in February 2025 to follow new state laws, and the city runs a Pre-Approved ADU Plan Program with an ADU FAQ, forms and a plan-check handout. This guide summarizes the numbers on the city’s ADU FAQ page, the pre-approved plan program, and what an ADU or unpermitted conversion means for a sale.

The ADU pages did not list setback numbers, fees or an owner-occupancy rule in the text we could read, so we leave them out. Confirm the current ordinance with Planning before you design.

Monrovia ADU rules at a glance

Ordinance	Updated February 2025 to follow state legislation; several state ADU laws took effect January 1, 2025
Unit size	Minimum 150 sq ft, maximum 1,000 sq ft; junior ADUs range from 150 to 500 sq ft
Height	16, 18 or 20 feet depending on the lot’s location and development
Front setback	State law bars a front yard setback requirement for ADU development and related mechanical equipment
Parking	Only for new ADUs over 800 sq ft that are not within 1/2 mile of a public transit stop
Pre-approved plans	City program; homeowners work with the design professional who prepared the plan, for a fee
Plan check	Submit plans electronically to building@monroviaca.gov

How Monrovia describes ADUs

The city’s FAQ defines an accessory dwelling unit as an attached or detached residential unit with complete independent living facilities on a lot with a proposed or existing primary residence. ADUs can be converted space or new construction.

The city gives a general range of 150 to 1,000 square feet for ADUs and says junior ADUs are smaller units of 150 to 500 square feet. Height limits are listed as 16, 18 or 20 feet depending on where the lot is and how it is developed, so ask Planning which applies to your parcel.

Pre-Approved ADU Plan Program

The city offers a catalog of pre-approved ADU plans that staff have already reviewed for key design and code requirements. Plans are available to the public, but residents must work with the design professional who prepared the plan, for a fee, and site-specific review for placement still applies.

The city also has a submission guide for designers and architects. If you are thinking about adding value before a sale, compare the cost and time of a pre-approved plan with selling the house as it stands.

Parking, setbacks and state law

The FAQ states that parking can be required only for newly constructed ADUs larger than 800 square feet that are not within a half mile of any public transit stop, including a public bus stop.

It also says state law prohibits a front yard setback requirement for ADU development and related mechanical equipment. The city’s overview notes that several new state ADU laws took effect on January 1, 2025, and that Monrovia updated its ordinance in February 2025 to match.

Because ADU law changes often, treat the city’s current ordinance as the final word.

Fire zones and plan check

If an ADU sits in a Very High Fire Hazard Severity Zone, the city’s plan-check handout says the plans must show all applicable details and notes under Section R337 of the 2019 California Residential Code.

The handout also asks for a site plan with setbacks, easements and utility meter locations, structural calculations if the design departs from conventional construction, Title 24 energy forms and CALGreen notes.

That is a lot of paperwork, which is one reason buyers often value a unit that already has a finaled permit.

Planning for Housing and other Planning pages

The city’s Planning section also has a Planning for Housing page, which says the housing element tracks projected ADU production and is reviewed annually in reporting to the state housing department. The Planning section also lists oak tree and historic preservation pages, so check those if your lot has a mature tree or an older home.

State ADU law and Monrovia

California’s ADU statute, Government Code section 66314 and following, sets a floor that every city must follow, and local ordinances fill in the details.

The state requires ministerial review within 60 days of a complete application, bars a city from requiring more than a limited set of standards, and generally allows an ADU or conversion inside existing space without added setbacks.

The California Department of Housing and Community Development (HCD) publishes a handbook and keeps a list of the state requirements. Because state law changes often, treat the city’s current ordinance and handout as the final word on size, height, parking and fees for your lot.

ADUs, garage conversions and selling a Monrovia house

Many older homes have a converted garage or a backyard unit built without permits. Buyers and lenders ask about them, and California sellers generally disclose known unpermitted work. Our guide to selling as-is with unpermitted work explains the rules, and our Prop 13 guide explains how new construction can affect property tax. Before you list:

• Check city records for permits on any ADU, conversion or addition.
• Ask Planning whether the structure could qualify under current rules.
• Estimate plans, fees and corrections needed to legalize it.
• Compare that with selling as-is and letting a cash buyer take on the legalization.

Questions to ask Planning before you design

• Does my lot and zone allow an ADU, a junior ADU, or both?
• Is a pre-approved or pre-reviewed ADU plan available?
• What are the current impact, utility and school fees for the size I am considering?
• Can my existing garage or accessory structure be converted without changing its footprint?
• Are there fire, slope, easement or utility constraints on my lot?

Junior ADUs and garage conversions in more detail

State law treats a junior ADU as a unit of up to 500 square feet created inside the walls of an existing or proposed single-family home, with an efficiency kitchen and a recorded restriction that keeps it from being sold apart from the house.

A garage conversion is a different path: the unit replaces the garage, and state law generally does not require the city to demand replacement parking. Both are common sources of unpermitted space in older Monrovia neighborhoods, which is why buyers’ agents and appraisers ask for the permit record.

If a conversion was done without a permit, the usual fix is to submit as-built drawings, pay the fees and pass inspection, which can take months and cost real money.

Fees, utilities and property tax

State law limits the impact fees a city can charge on smaller ADUs and on conversions of existing space, and it limits when a separate utility connection can be required.

Larger new units can still carry impact fees, school fees and water or sewer connection charges, so ask for an itemized estimate before you commit to plans. New construction is generally reassessed for property tax under Prop 13, which means an ADU can raise the bill for the whole property. Our Prop 13 guide explains how reassessment works.

Why ADUs matter for resale

A permitted ADU can add rental income and appeal for some buyers, but an unpermitted one can complicate financing and appraisal. Lenders typically want permitted living area, and an appraiser may not count unpermitted space.

Because an ADU generally cannot be sold separately from the main home, its value comes through the sale of the whole property.

If you inherited a house with an old backyard unit, or bought one with a converted garage, check what the city has on file before you decide how to sell. Our probate home sale guide covers inherited property.

How to sell a house in Monrovia

1. Check city records for permits on any ADU, conversion or addition.
2. Ask Planning whether the structure could qualify under current rules.
3. Request a no-obligation cash offer for the house as it stands.
4. Choose your closing date.
5. Close with no legalization, repairs or showings required.

See also our Monrovia page, the Monrovia as-is sale page, the inherited house page and the Los Angeles County hub.

Frequently asked questions

When did Monrovia update its ADU ordinance?

The city says it updated its ADU ordinance in February 2025 to follow state legislation.

How big can an ADU be in Monrovia?

The city’s FAQ gives a minimum of 150 square feet and a maximum of 1,000 square feet, with junior ADUs from 150 to 500 square feet.

Does Monrovia require ADU parking?

Only for newly constructed ADUs over 800 square feet that are not within a half mile of a public transit stop, according to the city’s FAQ.

Does Monrovia have pre-approved ADU plans?

Yes. The city runs a Pre-Approved ADU Plan Program; homeowners work with the design professional who prepared the plan.

How do I submit ADU plans?

The city’s plan-check handout says to submit plans electronically to building@monroviaca.gov.

Can I sell a house with an unpermitted ADU?

Yes. You can disclose it and sell as-is, including to a cash buyer. Lenders and appraisers may not count unpermitted space.

More guides

• We Buy Houses in Monrovia
• We Buy Houses in Los Angeles County
• Los Angeles County Property Tax Guide
• Monrovia Building Permits Guide
• Monrovia Code Enforcement Guide
• Sell Your Monrovia House As-Is
• Monrovia Cash Offer Process
• Sell My Monrovia House Fast
• All California Guides

Sources

• City of Monrovia: Accessory Dwelling Units
• City of Monrovia: ADU FAQs
• City of Monrovia: Pre-Approved ADU Plan Program
• City of Monrovia: ADU Plan Check Submittal Handout
• City of Monrovia: Planning for Housing
• California HCD: Accessory Dwelling Units

This guide is general information from public sources, not legal advice. Confirm current rules, fees and hours with the city.