Different insurance policies identify different events which trigger coverage. Two types of common insurance policies are "claims made" policies and "occurrence" policies.

Under a "claims made" policy, coverage is triggered when, during the policy period, an insured becomes aware of and notifies the insurer of either claims against the insured or situations that might give

Property damage that results from a continuous and ongoing process over an extended period of time rather than from a defined, identifiable event such as a tornado or hail damage creates disagreements and disputes as to when property damage "occurred."  Coverage under most insurance policies is triggered by an "occurrence."  As Dana Ferestien commented, insurers and insureds continue to litigate