Anti-Concurrent Causation Clauses: What They Are, Why They Matter, and Why California Ignores Them

Buried deep in the exclusions section of most standard homeowner policies is a clause that, in many states, gives insurance companies the power to deny an entire claim even when the primary cause of damage is a covered peril. It is called the anti-concurrent causation clause— or ACC clause — and it is one of the most insurer-friendly provisions in all of property insurance.

The clause typically reads something like this:

“We do not insure for loss caused directly or indirectly by any of the following. Such loss is excluded regardless of any other cause or event contributing concurrently or in any sequence to the loss.”

In plain English, this means: if anyexcluded peril is involved in causing your loss — even if it was a minor contributing factor, even if it came at the end of a chain of events started by a covered peril — the entire claim is denied. No apportionment. No partial payment. Nothing.

In most states, courts enforce this language exactly as written. But in California, the story is fundamentally different. California courts have held that anti-concurrent causation clauses are unenforceablewhen they conflict with the state’s efficient proximate cause doctrine. This article explains how ACC clauses work, why California rejects them, how other states treat them, and what this means for policyholders depending on where they live and what type of policy they have.

What Is an Anti-Concurrent Causation Clause?

An anti-concurrent causation clause is policy language that precedes certain exclusions — typically earth movement, water damage, neglect, government action, and nuclear hazard — and broadens them beyond their ordinary scope. Without an ACC clause, an exclusion applies only when the excluded peril is the actual cause of the loss. Withan ACC clause, the exclusion applies whenever the excluded peril is involved in the causal chain at all, “regardless of any other cause or event contributing concurrently or in any sequence to the loss.”

The ACC clause was introduced to standard ISO policy forms in 1986 as a direct response to the “concurrent causation” doctrine that courts in several states — including California — had developed in the 1970s and 1980s. Insurers saw courts ruling that when a covered and excluded peril combined to cause a loss, coverage existed. The ACC clause was designed to contract around those rulings and restore the insurer’s ability to deny coverage whenever an excluded peril was even marginally involved.

California Law: ACC Clauses Are Unenforceable

California is one of a small number of states where anti-concurrent causation clauses simply do not work. The reason is statutory: California Insurance Code §530, which has been on the books for over a century, establishes the proximate cause rule for insurance:

“An insurer is liable for a loss of which a peril insured against was the proximate cause, although a peril not contemplated by the contract may have been a remote cause of the loss; but he is not liable for a loss of which the peril insured against was only a remote cause.”

This statute means the question in every California claim is the same: what was the proximate, predominating cause of the loss? If a covered peril was the proximate cause, the loss is covered — even if an excluded peril also contributed. If the excluded peril was the proximate cause and the covered peril was merely a remote cause, the loss is not covered. The California Supreme Court calls this the efficient proximate cause doctrine, and it has been the law in California for over sixty years. For a detailed discussion of how this doctrine works, see our companion article on the efficient proximate cause doctrine.

The Landmark Cases

Three California Supreme Court decisions form the backbone of this area of law:

Sabella v. Wisler (1963) 59 Cal.2d 21.This is the foundational case. A builder negligently installed a sewer line, causing the pipe to rupture. Water from the broken sewer, combined with seasonal rain, caused the foundation to settle. The insurer denied the claim under an earth movement exclusion. The California Supreme Court rejected the denial and held that “in determining whether a loss is within an exception in a policy, where there is a concurrence of different causes, the efficient cause — the one that sets others in motion — is the cause to which the loss is to be attributed.” Because the builder’s negligence (a covered peril) set the chain in motion, the loss was covered despite the involvement of settling (an excluded peril).

Garvey v. State Farm Fire & Casualty Co. (1989) 48 Cal.3d 395.This is the California Supreme Court’s definitive first-party property damage decision on efficient proximate cause. The Garvey family discovered structural damage caused by a combination of negligent construction (covered) and earth movement (excluded). State Farm denied the claim. The Supreme Court held that the “efficient proximate cause” — the predominating cause that set the others in motion — controls. If the covered peril predominated, the loss is covered. The Court remanded for a jury determination of which peril predominated.

Julian v. Hartford Underwriters Ins. Co. (2005) 35 Cal.4th 747. This is the case that directly addressed anti-concurrent causation clauses. After Garvey, some insurers tried to circumvent the efficient proximate cause doctrine by adding ACC language to their exclusions — the very language discussed in this article. The California Supreme Court shut the door on that tactic. The Court held:

“[P]olicy exclusions are unenforceable to the extent that they conflict with section 530 and the efficient proximate cause doctrine.”

In other words, an insurer cannot use contractual language to give its exclusions broader effect than the efficient proximate cause analysis allows. The ACC clause — “regardless of any other cause or event contributing concurrently or in any sequence” — is exactly the kind of language that attempts to do this, and Julian says it does not work in California.

For a comprehensive discussion of these and other key California insurance decisions, see our article on California insurance case law.

The CDI Has Reinforced This Rule Repeatedly

The California Department of Insurance (CDI) has not left this to the courts alone. The CDI has issued formal guidance — twice — reminding insurers that they cannot rely on earth movement or flood exclusions to deny claims when a covered peril was the efficient proximate cause.

2018 Notice (Commissioner Dave Jones): After the 2017–2018 Thomas Fire and Montecito mudslides, the CDI issued a formal notice to all property and casualty insurance companies reminding them that mudflow exclusions are unenforceable where the efficient proximate cause of the mudslide was the wildfire. The notice referenced the holding in Howell v. State Farm Fire & Casualty Co. (1990) 218 Cal.App.3d 1446, where the Court of Appeal concluded that an insurer providing coverage under a property insurance policy may not contractually exclude coverage when an insured peril (such as fire) is the efficient proximate cause of a loss, regardless of other contributing causes.

Bulletin 2025-3 (Commissioner Ricardo Lara):Following the January 2025 Los Angeles wildfires, the CDI issued Bulletin 2025-3 on February 4, 2025, titled “Coverage of Flood, Mudslide, and Earth Movement Claims Relating to Recent Wildfires.” The bulletin states:

“If it is established that a recent wildfire or another peril covered by the applicable policy was the efficient proximate cause of the damage resulting from subsequent mudslides and other similar events following the fire, such damage is covered by the policy regardless of any exclusion in the applicable policy.”

The phrase “regardless of any exclusion” is critical. It means that even if your policy has an earth movement exclusion preceded by anti-concurrent causation language, the CDI’s position is that the exclusion cannot be used to deny coverage when fire set the chain of events in motion. For a detailed discussion of post-wildfire mudslide coverage, see our article on mudslide coverage after wildfire.

Policies Without ACC Language: DP-1 and DP-3 Forms

Not all property insurance policies contain anti-concurrent causation clauses. Two common dwelling fire policy forms — the DP-1 (Basic Form) and the DP-3 (Special Form) — do not include ACC language. This is a significant advantage for policyholders insured under these forms, and it is important to understand why.

DP-1: The California FAIR Plan’s Basic Fire Policy

The DP-1 is a named-peril policy — it covers only the specific perils listed in the policy, typically fire, lightning, internal explosion, and smoke. Because the DP-1 is a named-peril policy with a short list of covered perils, it does not need the broad exclusion structure found in HO-3 policies. There are no earth movement, water damage, or neglect exclusions preceded by ACC language because those perils were never covered in the first place. The DP-1 only pays when one of its listed perils causes the loss.

The California FAIR Plan — the state’s insurer of last resort for homeowners who cannot obtain coverage in the private market — issues DP-1 policies. For homeowners in wildfire-prone areas, this is often the only dwelling coverage available. For a detailed discussion of how the FAIR Plan works, see our guide to the California FAIR Plan.

DP-3: The Better Option in High-Risk Areas

The DP-3 is a special form (open-peril) policy that covers all causes of loss to the dwelling unless a specific exclusion applies. Despite being an open-peril policy like the HO-3, the standard DP-3 form does not contain the anti-concurrent causation language found in HO-3 policies. This means the DP-3 has the broader coverage scope of an open-peril form without the ACC clause that allows insurers to weaponize their exclusions.

In California, DP-3 policies are sometimes available from surplus lines carriers — including Lloyd’s of London syndicates — for properties in fire zones where admitted carriers will not write an HO-3. A DP-3 from a surplus lines carrier actually provides a structural advantage over a standard HO-3 in one critical respect: even if the policyholder is in a state that enforces ACC clauses, the DP-3’s lack of ACC language means the exclusion stands on its own terms, without the “regardless of any other cause” broadening effect.

Real-World Examples: How ACC Clauses Affect Claims

The impact of anti-concurrent causation clauses is best understood through concrete examples. These scenarios illustrate how the same physical event can produce entirely different insurance outcomes depending on (1) whether the policy contains ACC language and (2) what state the property is in.

Example 1: Car Hits a Fire Hydrant and Collapses a Roof

A car runs a stop sign and strikes a fire hydrant in front of a home. The hydrant shears off and sends a massive column of water into the air. The water lands on the roof, overwhelms the drainage, and the weight of the accumulated water causes a section of the roof to collapse. The vehicle never touched the building.

The causal chain is: vehicle impact → hydrant failure → water discharge → water accumulation on roof → roof collapse.

The efficient proximate cause of this loss is the vehicle impact. The vehicle is what set the entire chain of events in motion. Water accumulation on the roof was merely the mechanism through which the damage manifested — it was not the predominating cause. The vehicle did not need to physically strike the building for the vehicle to be the efficient proximate cause.

Under a standard HO-3 policy, vehicle impact is a covered peril. Even though water accumulation contributed to the collapse, the roof damage is covered because the vehicle started the chain. In California, this result holds regardless of whether the policy contains an ACC clause, because ACC clauses are unenforceable under Julian. In states that enforce ACC clauses, the result stilllikely favors the policyholder here, because the water did not come from a natural source — it came from a covered peril (vehicle damage to an artificial structure). But the analysis becomes more uncertain when the water issue is closer to an enumerated exclusion.

Example 2: Heavy Construction Vehicles Shake a Building

Heavy construction vehicles — loaded dump trucks, bulldozers, excavators — travel down a residential street daily for months as part of a road widening project. The vehicles do not strike any of the adjacent buildings. But the repeated heavy vibrations from the vehicles transmit through the ground and cause the walls of a nearby home to crack, the foundation to shift, and interior finishes to separate.

The causal chain is: vehicle operation → ground vibration (earth movement) → structural damage to the building.

Most property policies exclude earth movement. The HO-3 policy excludes “earth movement” including “earthquake, landslide, mudflow, mudslide, sinkhole, subsidence, erosion or movement of a body of mud or rock,” and that exclusion is preceded by the anti-concurrent causation clause: “regardless of any other cause or event contributing concurrently or in any sequence to the loss.”

Here is where the policy form and the state law both matter:

• DP-1 or DP-3 policy (any state):These forms do not contain ACC language. The earth movement exclusion, if it exists at all, stands on its own terms. The policyholder argues that the efficient proximate cause was the vehicle operation — a covered peril — and that the earth movement was merely the mechanism through which the vehicle’s energy reached the building. Without ACC language, the insurer cannot invoke the “regardless of any other cause” broadening. The analysis turns on standard causation principles.
• HO-3 policy in California: Even though the HO-3 contains ACC language, Julian v. Hartford Underwriterssays that language is unenforceable to the extent it conflicts with §530 and the efficient proximate cause doctrine. The policyholder argues that the vehicle operation was the efficient proximate cause. If a trier of fact agrees, the loss is covered despite the earth movement exclusion and despite the ACC clause.
• HO-3 policy in a state that enforces ACC clauses (e.g., Texas, Florida, New York):The insurer points to the ACC clause and argues that because earth movement contributed to the loss — in any sequence — the entire claim is excluded. In most ACC-enforcing states, the insurer wins this argument. It does not matter that the vehicle was the predominating cause. The ACC clause eliminates the need for the insurer to prove that the excluded peril was the predominant cause — any involvement of the excluded peril, at any point in the chain, is enough.

Example 3: Wildfire Followed by Mudslide

A wildfire burns through a hillside neighborhood, destroying vegetation and destabilizing the soil. Two months later, heavy rains arrive. Without the vegetation to hold the soil in place, a mudslide cascades down the hill and damages homes at the base. The homes were not damaged by the fire itself.

The causal chain is: wildfire → vegetation loss → soil destabilization → rain → mudslide → property damage.

Fire is a covered peril under every property policy. Earth movement (including mudslide) is excluded under most policies. The question is whether the fire’s role as the event that stripped the hillside is enough to make it the efficient proximate cause of the mudslide damage.

In California, the answer is yes — and both the courts and the CDI have said so. The Court of Appeal in Howell v. State Farmheld that fire was the efficient proximate cause of a subsequent landslide, and CDI Bulletin 2025-3 explicitly states that mudslide damage following a wildfire is covered “regardless of any exclusion in the applicable policy.” The ACC clause cannot save the insurer.

In a state that enforces ACC clauses, the insurer would argue that the earth movement exclusion — preceded by ACC language — eliminates coverage because a mudslide (an excluded peril) contributed to the loss “in any sequence.” In many of those states, the insurer wins. This is one of the most consequential differences in property insurance law between California and the majority of other states.

For a deeper analysis of this specific scenario, see our article on wildfire and mudslide coverage.

California vs. Other States: A National Comparison

The treatment of anti-concurrent causation clauses varies dramatically from state to state. Understanding where your state falls is essential to knowing whether your policy’s ACC language has teeth.

States That Refuse to Enforce ACC Clauses

A small number of states have statutes or court decisions that prevent insurers from contracting around the proximate cause rule through ACC language. California is the most prominent, based on Insurance Code §530 and the Julian decision. Other states in this category include North Dakota, Washington, and West Virginia, where courts have held that ACC clauses violate public policy or conflict with state insurance statutes.

States That Enforce ACC Clauses

The majority of states enforce ACC clauses on the basis of freedom of contract. Courts in these states reason that the policyholder and insurer agreed to the policy terms, and the ACC clause unambiguously states the conditions under which the exclusion applies. States where courts have upheld ACC clauses include Texas, Florida, New York, Alabama, Arizona, Colorado, Indiana, Louisiana, Massachusetts, Michigan, New Jersey, Pennsylvania, South Carolina, and Tennessee, among others.

In these states, the practical effect is severe: if 99% of a loss was caused by a covered peril (like wind) and 1% was attributable to an excluded peril (like flood), the ACC clause allows the insurer to deny the entire claim. No apportionment. No pro-rata payment. The involvement of the excluded peril, in any amount and at any point in the causal chain, is enough to trigger the exclusion.

Side-by-Side Comparison: The Same Loss in California vs. Texas

Common Misconceptions About ACC Clauses

Misconception 1: “If my policy says it’s excluded, it’s excluded.”

This is the most dangerous misconception. In California, the policy language is the starting point, not the final word. Insurance Code §530 is a mandatory rule of California insurance law. Insurers cannot contract around it. When the policy language conflicts with §530, the statute controls. The ACC clause is a contractual provision that attempts to override a statutory rule — and in California, the statute wins.

Misconception 2: “The ACC clause only matters when two causes act simultaneously.”

The ACC clause explicitly covers causes acting “concurrently or in any sequence.” It is designed to capture both simultaneous causation (two causes acting at the same time) and sequential causation (one cause leading to another). The fire-then-mudslide scenario is a sequential causation case, and the ACC clause by its terms purports to exclude it. That is precisely why the clause is so dangerous in states that enforce it — and why California’s refusal to enforce it is so significant.

Misconception 3: “The efficient proximate cause doctrine only applies to fire.”

The doctrine applies to any covered peril that sets a chain of events in motion. Fire is the most commonly litigated scenario because of the wildfire-mudslide sequence, but the doctrine has been applied in cases involving third-party negligence, defective construction, vehicle impacts, vandalism, and other covered perils. If a covered peril is the efficient proximate cause and an excluded peril is merely a link in the chain, the loss is covered in California regardless of what the excluded peril is.

What ACC Clauses Mean for Coverage Disputes

If you are a California policyholder and your insurer has denied a claim by citing an exclusion preceded by anti-concurrent causation language, the denial is not necessarily the final word. You should consider:

• Identify the causal chain. What was the first event? What did it set in motion? What actually caused the physical damage to your property? If a covered peril started the chain, you have an efficient proximate cause argument.
• Check your policy form. Is your policy an HO-3, a DP-1, or a DP-3? If it is a DP-1 or DP-3, the ACC language may not be present at all, making your argument even more straightforward.
• Document the sequence of events.Photographs, videos, weather records, contractor reports, engineering assessments — anything that establishes the causal chain and supports the argument that the covered peril was the predominating cause.
• Know the key authorities. California courts have consistently upheld the efficient proximate cause doctrine over anti-concurrent causation clauses. As attorney John L. Corbett of Barnes & Thornburg LLP has noted, “California courts have repeatedly held that insurers cannot contract around the statutory mandate for efficient proximate cause with an ACC clause.” The key authorities are Insurance Code §530, Sabella v. Wisler, Garvey v. State Farm, and Julian v. Hartford Underwriters. If the loss involves a post-wildfire mudslide, CDI Bulletin 2025-3 adds regulatory weight. If your insurer has denied coverage based on an ACC clause, discuss these authorities with your attorney.
• Get help early. Efficient proximate cause arguments are fact-intensive and often require expert analysis to establish the causal chain. A licensed Public Adjuster can help build the factual case, and an attorney may be needed if the insurer refuses to engage.

Understanding Policy Exclusions With and Without ACC Language

The presence or absence of ACC language changes how an exclusion operates. Consider the earth movement exclusion as an example:

• Without ACC language (DP-1, DP-3): The exclusion applies when earth movement is the cause of the loss. If the policyholder can show that the earth movement was itself caused by a covered peril (like a vehicle, construction activity, or fire), the exclusion is analyzed under standard causation principles. The exclusion only bars coverage if the earth movement was the predominating cause.
• With ACC language, in California (HO-3): The exclusion contains the broadening ACC clause, but the clause is unenforceable under Julian. The analysis is the same as above — the question is whether the covered peril was the efficient proximate cause.
• With ACC language, in an ACC-enforcing state(HO-3): The exclusion is broadened by the ACC clause. If earth movement contributed to the loss in any way, at any point in the sequence, the exclusion applies and coverage is denied — even if a covered peril was the predominating cause.

Key Takeaways

• Anti-concurrent causation clauses are designed to broaden exclusions by eliminating coverage whenever an excluded peril contributes to a loss “in any sequence.” In most states, they work exactly as intended.
• In California, ACC clauses are unenforceable under Insurance Code §530 and the California Supreme Court’s decision in Julian v. Hartford Underwriters Ins. Co. (2005) 35 Cal.4th 747. The efficient proximate cause doctrine controls.
• DP-1 and DP-3 policy forms do not contain ACC language in the first place. If your policy is a DP-1 (like a California FAIR Plan policy) or a DP-3 (like policies sometimes available from surplus lines carriers in fire zones), the exclusions stand on their own terms without the ACC broadening.
• The California Department of Insurance has twice issued formal guidance — in 2018 and in Bulletin 2025-3 — confirming that mudslide and earth movement exclusions cannot be used to deny coverage when a wildfire was the efficient proximate cause.
• The same physical loss can be covered in California and denied in Texas, Florida, New York, and most other states, solely because of differences in how each state treats ACC language.
• If your insurer is relying on an ACC clause to deny your California claim, you have strong legal authority to push back. Document the causal chain and get professional help early.