The concurrent cause rule basically holds that if two or more events cause a loss, with one being excluded under the policy terms and the other(s) being covered, the policy should provide coverage for the loss.

As discussed in Davidson Hotel Co. v. St. Paul Fire and Marine Insurance Co., 136 F. Supp. 2d 901 (2001), this rule allows for coverage “where the loss is essentially caused by an insured peril with the contribution of an excluded peril merely as part of a chain of events leading to the loss.” The thinking behind this ruling and other concurrent causation cases is that the cause of loss that is not excluded caused damage to the insured's property in one way or another, so the property coverage form must pay for the loss.

As a modification of the concurrent cause rule, some courts developed the efficient proximate cause rule. Couch on Insurance states that this rule permits recovery for a loss caused by both a covered cause of loss and an excluded cause of loss if the covered cause was the efficient proximate cause of the loss. That is, the covered cause set the other causes in motion that, in an unbroken sequence, produced the result for which recovery is sought. (Note that courts have not reached a consensus on the precise definition of efficient proximate cause, although most jurisdictions do require an analysis of the events to determine the nearness or proximity of the cause to the effect.)