Property damage rarely has a single, clean cause. A hurricane brings wind and flood. A pipe bursts because of age and freezing temperatures. A roof leaks because of storm damage and deferred maintenance. When two or more causes contribute to a single loss — and one cause is covered while the other is excluded — the question of how the claim should be handled becomes one of the most complex and contested issues in insurance law.
This is the problem of concurrent causation, and it lies at the center of many of the most significant claim disputes between policyholders and carriers.
What Concurrent Causation Means
Concurrent causation occurs when two or more independent causes combine to produce a single, indivisible loss. The classic example is a hurricane that causes both wind damage (typically covered) and flood damage (typically excluded under a standard homeowners policy). If the wind and flood damage can be separated — wind damaged the roof, flood damaged the first floor — each component can be evaluated independently. But when the causes cannot be separated — when it is impossible to determine whether the water inside the home entered through the wind-damaged roof or rose from the flood — the question becomes whether the entire loss is covered, partially covered, or excluded.
The legal treatment of concurrent causation varies significantly by jurisdiction. Some states follow the "concurrent causation doctrine," which generally holds that if a covered peril is a contributing cause of the loss, the entire loss is covered — even if an excluded peril also contributed. Under this approach, the presence of a covered cause is sufficient to trigger coverage, and the carrier cannot avoid payment simply because an excluded cause was also at work.
The Anti-Concurrent Causation Clause
In response to the concurrent causation doctrine, insurance carriers began adding anti-concurrent causation (ACC) clauses to their policies. These clauses typically state that the policy does not cover a loss caused by an excluded peril regardless of whether a covered peril contributed to the loss, whether the excluded peril acted concurrently or in sequence with a covered peril, and regardless of whether the excluded peril was the proximate or remote cause.
The practical effect of an ACC clause is to give the exclusion priority over the coverage grant. If flood is excluded and an ACC clause is present, any loss to which flood contributed — even partially, even in combination with a covered peril like wind — may be denied in its entirety.
ACC clauses are now standard in most homeowners and commercial property policies. Their enforceability, however, varies by state. Some jurisdictions enforce ACC clauses as written, holding that the policy language is clear and unambiguous. Others have limited or rejected their application, particularly when the excluded peril was a remote cause or when enforcing the clause would effectively eliminate coverage that the policyholder paid for.
How Courts Analyze the Issue
Courts generally apply one of several analytical frameworks to concurrent causation disputes.
The efficient proximate cause doctrine, followed in some states, looks at which cause set the loss in motion and was the predominant cause. If the efficient proximate cause is a covered peril, the loss is covered — even if an excluded peril also contributed. If the efficient proximate cause is excluded, the loss is not covered.
The concurrent cause doctrine, as described above, favors coverage whenever a covered peril is among the contributing causes.
The anti-concurrent causation approach defers to the policy language and enforces the ACC clause, denying coverage whenever an excluded peril is a contributing cause — regardless of the role played by the covered peril.
The framework that applies depends entirely on state law, and the differences between jurisdictions can produce opposite outcomes on identical facts. A windstorm and flood loss that is fully covered in one state may be fully denied in another, based solely on how the court interprets the interaction between the covered peril, the excluded peril, and the policy language.
Practical Implications for Policyholders
Policyholders dealing with a concurrent causation situation should take several steps to protect their claim.
First, document the damage as thoroughly as possible and attempt to distinguish between damage caused by the covered peril and damage caused by the excluded peril. Photographs, videos, expert assessments, and meteorological data can all help establish which cause produced which damage. Even in situations where the loss appears indivisible, evidence that supports separating the causes strengthens the argument for at least partial coverage.
Second, review the policy for an anti-concurrent causation clause. Knowing whether the clause is present — and understanding how courts in the applicable state have interpreted it — is essential for evaluating the strength of the coverage position.
Third, consult with a professional who understands concurrent causation law in the relevant jurisdiction. These disputes involve complex legal questions that are highly fact-specific and jurisdiction-dependent. A knowledgeable public adjuster or insurance attorney can help develop the strongest possible argument for coverage.
Key Takeaway
When multiple causes produce a single loss, the claims process becomes a legal and factual analysis rather than a straightforward damage assessment. The outcome depends on the policy language, the applicable state law, and the quality of the evidence documenting what caused what. Policyholders who understand the concept of concurrent causation — and who take steps to document and separate causes of loss from the outset — are better positioned to recover what the policy should provide.