Can the city deny my ADU because of code violations on my existing house?

Usually not. State law bars a city or county from denying an ADU or JADU permit because of nonconforming zoning conditions, building code violations or unpermitted structures on your property, unless the problem threatens public health and safety and is affected by building the ADU. If a condition meets both tests, the agency can require it to be addressed.

The rule

Government Code section 66322(b) says a local agency shall not deny an ADU permit due to the correction of nonconforming zoning conditions, building code violations or unpermitted structures that do not present a threat to public health and safety and are not affected by the construction of the ADU. Section 66336 applies the same rule to JADUs. For the state-protected ADU types in section 66323, agencies also cannot require correction of nonconforming zoning conditions as a condition of approval.

HCD's handbook puts it this way: an ADU application may be denied due to building code violations on the primary unit only if the violations present a threat to public health and safety and are affected by the construction of the ADU. The ADU itself must still fully comply with the building code.

How the two tests can play out

• Generally not a basis for denial: an older house that does not meet today's setbacks, or an unpermitted patio cover on the far side of the lot that the ADU work does not touch.
• Could be: hazards tied directly to the ADU work, such as an existing electrical service or panel with a dangerous condition that will feed the ADU, or a damaged sewer line the ADU will drain into.

Whether a particular condition qualifies is decided by your building department. If the unpermitted structure is the ADU itself, a different law applies: section 66311.7 limits denial of permits for unpermitted ADUs built before January 1, 2020, with exceptions for health and safety and for substandard buildings.

What this means for your MEP plans and permit set

Your MEP plans show where the ADU connects to existing systems: the main panel or service, the sewer lateral, the water service and any gas line. Those connection points are exactly where an existing defect can become affected by the construction. Before design is final, have the existing panel, service and sewer lateral evaluated, and show any needed corrections on the plans instead of waiting for an inspector to find them. See the ADU amnesty law, sewer lateral inspections, panel upgrades for ADUs, and the California ADU permit guide. Confirm how your jurisdiction applies these tests with your building department.

Sources: leginfo.legislature.ca.gov, leginfo.legislature.ca.gov, leginfo.legislature.ca.gov, hcd.ca.gov.