#1 ADU Contractor in Monrovia
Custom Builds by Horizon Remodeling

Finding the right adu contractor in Monrovia means understanding both the state rules that govern approvals and the local realities that shape what actually gets built on a given parcel. California consolidated its ADU statutes into Government Code sections 66310 through 66342 in 2024, and another round of changes took effect January 1, 2026. Under those updated rules, square footage is measured as interior livable space, an agency has 15 business days to determine whether a submitted application is complete, and 60 days to approve or deny it. Approval is ministerial, meaning no public hearing and no discretionary design review stands between a compliant application and a permit.

In Monrovia, that application goes to the City of Monrovia Community Development Department Building Division. That detail matters because Los Angeles County contains 88 incorporated cities, and the counter, the staff, and the local procedures change from one city to the next even when the underlying state law does not. A local handout picked up at a neighboring city’s building counter may not reflect what Monrovia’s division currently requires, which is one reason we review the applicable rules before any drawings are prepared.

One factor that sets Monrovia apart from many surrounding cities is its historic preservation program. The city has designated 164 landmarks under its 1995 preservation ordinance, and any work on those properties is subject to review by Certificate of Appropriateness. Mills Act contracts are available to qualifying owners, which can affect both project planning and long-term carrying costs. If your parcel or an adjacent structure falls within a designated area such as the Wildrose or Encinitas Historic Districts, we account for that review layer from the start rather than discovering it mid-permit.

The housing stock here also shapes the practical side of every project. Monrovia developed in waves from the 1886 to 1887 townsite boom through the Pacific Electric streetcar years and into the 1920s, when the city set a building permit record in 1923. Those older foothill homes typically have rooms and kitchens sized to their era rather than to contemporary open plans, which affects where a detached unit can sit, how far utilities have to run, and whether a garage conversion or a new detached structure makes more sense. We walk each parcel and check setbacks, grade, equipment access, and utility routes before a line is drawn.

Whatever the lot looks like, state law sets a floor that local agencies cannot go below. A city cannot cap an ADU below 850 square feet of interior livable space, or 1,000 square feet for a unit with more than one bedroom. Side and rear setbacks cannot exceed four feet. Owner-occupancy cannot be required as a condition of building an ADU. Construction of the unit cannot trigger a fire sprinkler retrofit of the primary residence. And there are no impact fees on any unit of 750 square feet or less. These protections apply regardless of where in the county a parcel sits, including in the county’s unincorporated areas, where the county’s own ADU ordinance was found non-compliant with state law by the California Department of Housing and Community Development in December 2025, a useful reminder that no local document should be treated as final without cross-checking it against current statute.