Concurrent Causation
Written by Justin Goodman, CIC, CISC, CLCS, CEO and Co-Founder, Total CSR
Published: August 31, 2026 · Last reviewed: August 31, 2026
In plain language: Concurrent causation happens when two things cause damage to a home or building at the same time, like a windstorm knocking down a wall while flooding also fills the basement. If one cause is covered and the other is excluded, the outcome depends entirely on the policy's wording.
Technical definition: Concurrent causation describes a loss produced by two or more perils acting together or in sequence, where at least one peril is covered and one is excluded. Courts and policy language, particularly anti-concurrent causation clauses, determine whether coverage applies when causes cannot be cleanly separated.
Concurrent Causation at a Glance
| Attribute | Detail |
|---|---|
| Also known as | Concurrent causation doctrine, combined-peril loss |
| Category | Property policy coverage principle |
| Lines of business | Homeowners, Commercial Property, Dwelling Fire, Flood |
| Industries most affected | Real estate, habitational, coastal and flood-prone construction |
| Related forms or endorsements | HO 00 03 (Homeowners 3 Special Form), ISO CP 10 30 (Causes of Loss – Special Form) |
| Who bears the risk | Policyholder, unless a covered peril is proven to independently cause the damage |
| Common solution | Separate flood or earthquake policy to close the gap left by anti-concurrent causation language |
| Also interacts with | Efficient proximate cause doctrine, named perils exclusions, wind-driven rain disputes |
Key Takeaways
- Concurrent causation describes a loss where a covered peril and an excluded peril combine, often at the same moment, to damage the same property.
- Agencies must understand this concept because it directly determines whether a claim gets paid or denied when hurricane wind and storm surge, or fire and earth movement, strike together.
- The most common misunderstanding is assuming an all-risk policy automatically pays if any part of the cause is covered; anti-concurrent causation clauses in most modern forms reverse that assumption.
- A quick win for agencies is proactively offering flood and earthquake coverage in every coastal or seismic account review, documented in the file, to close the concurrent causation gap before a claim ever happens.
What Is Concurrent Causation in Insurance?
Concurrent causation is a legal and underwriting concept describing what happens when a loss cannot be traced to a single cause. Property claims rarely arise from one clean event. A hurricane brings wind, rain, and storm surge together. An earthquake can trigger a fire. When one of those forces is covered and another is excluded, insurers and courts must decide how to apportion or deny the claim.
The doctrine exists because courts historically applied "efficient proximate cause," paying claims if the dominant, triggering cause was covered, even if an excluded peril contributed. Insurers pushed back with anti-concurrent causation (ACC) clauses, which state that if an excluded peril contributes to a loss in any sequence, no matter how minor, the entire loss is excluded. This shifted enormous risk back onto policyholders, particularly for flood and earth movement.
A concrete example illustrates the stakes. A coastal home loses its roof to hurricane wind, a covered peril under the homeowners policy. Storm surge then floods the first floor, an excluded peril under most homeowners forms. Without flood insurance, the ACC clause in the homeowners policy can deny the entire first-floor loss, even though wind caused the roof damage seconds earlier, because flood contributed to the combined loss.
How Does Concurrent Causation Work?
- The triggering event. A single storm, earthquake, or other occurrence sets multiple forces in motion, such as high wind combined with rising water.
- The combined damage. Both perils affect the same property, often the same structure or even the same room, making it difficult to isolate which peril caused which portion of the loss.
- The policy review. The adjuster examines the policy's causation language, specifically whether an anti-concurrent causation clause exists and how the exclusion for the non-covered peril is worded.
- The causation determination. The insurer determines whether the covered peril can be proven as an independent, separable cause of some or all of the damage, or whether the perils are too intertwined to separate.
- The claim outcome. Coverage is either paid in full, paid in part for the segregable covered-peril damage, or denied entirely under the ACC clause, depending on jurisdiction and policy language.
Real Claim Examples Involving Concurrent Causation
Hurricane wind and storm surge on a coastal home
A homeowner near the Gulf Coast suffered roof damage from hurricane-force wind and first-floor flooding from storm surge during the same landfall event. The homeowners policy covered wind but excluded flood, and it contained an anti-concurrent causation clause. The insurer paid for the roof but denied the flood-related contents and structural loss, and the homeowner had no separate flood policy to cover the gap.
Earthquake-triggered fire in a commercial building
A commercial property in a seismic zone experienced a fire that started after an earthquake ruptured a gas line. The commercial property policy excluded earth movement but covered fire. Courts in that jurisdiction applied efficient proximate cause rather than an ACC clause, and the fire damage was covered because fire was deemed the operative, covered cause even though the earthquake set it in motion.
Water intrusion after wind-damaged roof during a rainstorm
A homeowner's roof was damaged by wind, and rain then entered through the opening over several hours, causing interior water damage. The insurer initially argued the rain damage was excluded as water damage from an opening, but because the wind was the efficient proximate cause of the opening, most policies and courts treat the resulting water damage as a covered consequence of the covered wind peril, distinguishing this from true concurrent causation with an unrelated excluded peril.
Concurrent Causation vs. Efficient Proximate Cause: What Is the Difference?
Concurrent causation describes the factual situation where two or more perils combine to cause a loss, while efficient proximate cause is the legal doctrine some courts use to resolve which cause controls coverage. Insurers use anti-concurrent causation clauses specifically to override the efficient proximate cause doctrine and shift the outcome toward denial when any excluded peril is involved.
| Comparison area | Concurrent Causation | Efficient Proximate Cause |
|---|---|---|
| Primary use case | Describing losses with multiple contributing perils | Determining which contributing cause controls the coverage decision |
| Coverage / concept type | Factual scenario or policy clause trigger | Legal doctrine applied by courts |
| Typical exclusions | Flood, earth movement, water backup often excluded from the covered side | Not an exclusion itself; a rule for interpreting exclusions |
| Who is most affected by errors | Policyholders in coastal or seismic zones without layered coverage | Adjusters and attorneys misapplying jurisdiction-specific rules |
| Common mistakes | Assuming any covered peril in the mix guarantees payment | Applying the doctrine in a state that enforces ACC clauses instead |
What Are the Most Common Mistakes With Concurrent Causation?
- Assuming a standard homeowners or commercial property policy will pay a claim because wind, a covered peril, was involved, without checking for an anti-concurrent causation clause that excludes the entire loss.
- Failing to recommend separate flood or earthquake coverage for clients in high-risk zones, which creates a foreseeable coverage gap and significant E&O exposure when a combined loss occurs.
- Treating efficient proximate cause and anti-concurrent causation as interchangeable, when the applicable rule varies by state and by the exact policy wording.
- Neglecting to document conversations where flood or earthquake coverage was offered and declined, leaving the agency without proof of disclosure if a concurrent causation denial is later disputed.
- Overlooking policy differences between homeowners forms and commercial property forms, since ACC clause wording is not standardized across all ISO forms or carrier proprietary forms.
How to Explain Concurrent Causation to a Client
Explaining Concurrent Causation to a personal lines client
Your homeowners policy covers some perils, like wind, but not others, like flood. When a storm causes both at the same time, your policy may not pay for any of the damage if flood contributed, even a little. That is why we strongly recommend a separate flood policy if you are anywhere near water or in a flood zone.
Explaining Concurrent Causation to a small business owner
Your commercial property policy has specific covered causes of loss and specific exclusions, and problems happen when both occur in the same event. If an earthquake and a fire hit your building together, your fire coverage might not help if the policy language ties the fire back to the excluded earth movement. We should review your causes-of-loss form together so you know exactly where the gaps sit.
Explaining Concurrent Causation to a CFO or risk manager
Your property program's anti-concurrent causation language determines how claims get adjusted when multiple perils interact, which is common in catastrophic events. This exposure is not theoretical; it shows up in real hurricane and earthquake claims where courts have upheld full denials despite a covered peril contributing to the loss. We recommend a program-wide review of your ACC clause wording alongside your flood and earthquake sublimits to quantify this gap before renewal.
Frequently Asked Questions About Concurrent Causation
What is an anti-concurrent causation clause?
An anti-concurrent causation clause is policy language stating that if an excluded peril contributes to a loss in any sequence with a covered peril, the entire loss is excluded. Most modern homeowners and commercial property forms include some version of this clause, which is why flood and earthquake are almost always sold as separate policies.
Does concurrent causation always result in a denied claim?
Not always. Some states do not enforce anti-concurrent causation clauses and instead apply efficient proximate cause, which can result in coverage if the dominant cause was a covered peril. The outcome depends heavily on the jurisdiction, the specific policy wording, and whether the causes can be factually separated.
Can concurrent causation apply to auto or liability policies?
Concurrent causation most commonly arises in property insurance, but similar causation disputes can occur in other lines where multiple factors contribute to a single loss. The doctrine's practical impact and the anti-concurrent causation clause itself are almost exclusively property-policy concepts.
How can an agency reduce concurrent causation exposure for clients?
Agencies reduce exposure by identifying clients in flood zones, seismic regions, or coastal areas and proactively offering flood and earthquake policies alongside the primary property policy. Documenting the offer and any client decline in the agency management system creates a defensible record if a combined-peril claim is later denied.
Is concurrent causation the same as an exclusion?
Concurrent causation is not an exclusion itself; it is the scenario that triggers how exclusions and anti-concurrent causation clauses get applied. The exclusion for flood or earth movement is what ultimately denies coverage, but concurrent causation describes why that exclusion becomes relevant when a covered peril is also present.
Why do insurers use anti-concurrent causation clauses instead of relying on courts?
Insurers added anti-concurrent causation clauses after courts frequently ruled in favor of policyholders under the efficient proximate cause doctrine, which insurers viewed as expanding coverage beyond intended limits. The clauses give carriers clearer contractual grounds to deny combined-peril losses involving flood or earth movement, shifting interpretation away from judicial discretion.
Related Insurance Terms
- Efficient Proximate Cause: A legal doctrine holding that coverage follows the dominant, triggering cause of a loss even when a secondary excluded peril contributes, often in direct tension with anti-concurrent causation clauses.
- Anti-Concurrent Causation Clause: Specific policy language excluding an entire loss whenever an excluded peril contributes alongside a covered peril, regardless of sequence, and the primary mechanism carriers use to control concurrent causation exposure.
- Named Perils Policy: A policy that only covers losses from perils specifically listed, reducing concurrent causation disputes because unlisted perils are automatically excluded rather than argued over.
- All-Risk Policy: A policy covering all causes of loss except those specifically excluded, which is precisely the policy structure that makes concurrent causation disputes most likely to arise.
- Excluded Peril: A cause of loss the policy specifically does not cover, and the necessary counterpart to a covered peril in any concurrent causation scenario.
- Flood Insurance: A separate policy, often through the National Flood Insurance Program, that fills the coverage gap left when a homeowners or commercial property policy's anti-concurrent causation clause excludes flood-related damage.
Sources and References
- International Risk Management Institute (IRMI). Anti-Concurrent Causation.
- International Risk Management Institute (IRMI). Efficient Proximate Cause.
About the Author
Justin Goodman, CIC, CCIP, CISC, CLCS, CRIS, PCIA, QCLS, MFHR CEO and Co-Founder, Total CSR, Inc.
Justin Goodman is a third-generation insurance broker with over two decades in agency operations. He has trained more than 100,000 CSRs, account managers, and producers in commercial and personal lines coverage, from workers' compensation to construction risk. He was named 2024 Insurance Journal Agent of the Year and one of the nation's top five construction insurance experts by Risk & Insurance. He is the author of Retain, which applies cognitive science research on memory and knowledge transfer to insurance training, and speaks nationally on how agencies build durable technical expertise in their teams.