#1 ADU Contractor in Downey
Custom Builds by Horizon Remodeling

Finding the right adu contractor in Downey means understanding both the state rules that shape every project and the local conditions that shape yours. California codified its ADU law in Government Code sections 66310 through 66342, and the statute changed again on January 1, 2026. Square footage is now measured as interior livable space rather than gross area, and once you submit an application, the reviewing agency has 15 business days to determine whether it 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 complete application and a decision.

In Downey, that application goes to the City of Downey Building Safety Division. No unusual local overlay applies here, so the governing factors are the state building code and the age of your house. That second point matters more than it might seem. The typical Downey home is a single-story postwar tract house built around the time the city incorporated in 1956, and many of those homes have never had their utility systems or foundations touched since original construction. Older infrastructure affects how far electrical and sewer connections have to run to reach a new unit, which in turn affects cost and feasibility.

The postwar lot layout also shapes the choice between a detached build and a garage conversion. A single-story ranch footprint often leaves a detached garage at the rear of a relatively shallow lot, and we walk each parcel to check setbacks, grade, utility routes, and equipment access before a single line gets drawn. What looks straightforward from the street can present real constraints once you are standing at the back of the property.

Los Angeles County contains 88 incorporated cities, and the permit counter changes from one to the next even when the underlying state rules do not. One county-level point is worth noting for context. The county’s own ADU ordinance, amended in July 2025 and covering only unincorporated territory, was found non-compliant with state law by the California Department of Housing and Community Development in December 2025. Among other findings, it caps detached ADUs on a multifamily lot at two where state law allows up to eight. Downey is incorporated and not subject to that ordinance, but the situation is a useful reminder that a locally printed handout is not always current with the statute.

State law sets a floor of protections that applies regardless of which city’s counter you stand at. A local agency cannot cap an ADU below 850 square feet of interior livable space, or below 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 approval. Building an ADU cannot trigger a fire sprinkler retrofit of the primary home. And there are no impact fees on any unit of 750 square feet or less. We review these protections with every client before the design process begins so nothing gets left on the table.