While I have not performed exhaustive research into the origin of anti-concurrent causation (“ACC”) endorsements on insurance policies, or how or when they migrated from first-party property policies to commercial general liability (“CGL”) policies, they have done so. The result for Colorado’s construction professionals may rear its ugly head as an unwelcome and surprise outright declination of coverage for construction defect claims.

ACC endorsements state that if there are two causes of damage: one of which is covered by a policy and one of which is not, the carrier can invoke the ACC endorsement to disclaim coverage for all of the damage. An exemplar ACC endorsement is ISO Form CG 21 67, entitled “Fungi or Bacteria Exclusion.”