Contra Costa County, CA Rental Property Rules: Mold Disclosure (2026)

Unincorporated Contra Costa County defers to California state law on mold disclosure. Under Civil Code Section 1940.9 and Health & Safety Code Sections 26140 through 26156 (Toxic Mold Protection Act of 2001), landlords must provide written disclosure to prospective and current tenants when they know or reasonably should know visible mold exceeds permissible exposure levels or threatens health. The Department of Public Health has not finalized statewide permissible exposure limits, so disclosure is triggered primarily by visible mold or known water intrusion. Contra Costa Health Services investigates habitability complaints involving mold under California Health & Safety Code Section 17920.3 (substandard housing), which classifies dampness and mold as habitability defects warranting code enforcement. Tenants may withhold rent, repair and deduct, or sue under implied warranty of habitability.