PERSONAL INJURY | 2026-09-30

Two Causes, One Loss: The Efficient Proximate Cause Rule in California Insurance

When a loss results from both a covered and an excluded peril, California decides coverage by the predominant cause — the efficient proximate cause — not by whichever cause the insurer prefers.

Many property losses have <strong>more than one cause</strong>. A home may be damaged by a combination of a covered peril (say, a negligent act or a burst pipe) and an excluded one (say, earth movement). When covered and excluded causes combine to produce a single loss, which controls? California an

When a covered and an excluded peril both contribute to a loss, the outcome turns on which one predominates.

The Concurrent Causation Problem

Insurance policies cover some perils and exclude others. But real-world losses often result from multiple causes acting together — a phenomenon called concurrent causation. If one cause is covered and another is excluded, a rule is needed to decide whether the loss is covered. Without such a rule, insurers and policyholders could each point to the cause that favors their position, producing arbitrary results.

The Efficient Proximate Cause Rule

California resolves this with the efficient proximate cause doctrine. When a loss has concurrent causes, coverage is determined by the predominant cause that set the other causes in motion — the efficient proximate cause. If the efficient proximate cause is a covered peril, the loss is covered, even though an excluded peril also contributed. Conversely, if the efficient proximate cause is an excluded peril, the loss is excluded, even if a covered peril played a contributing role. The doctrine is codified in part in Insurance Code § 530, which provides that an insurer is liable for a loss whose proximate cause is an insured peril, even if a remote cause was excluded.

Garvey v. State Farm

The California Supreme Court’s decision in Garvey v. State Farm Fire & Casualty Co. is the leading authority. Garvey clarified that in first-party property cases involving concurrent causes, the efficient proximate cause analysis governs coverage — the trier of fact identifies the predominant cause of the loss, and coverage follows that cause. The Court distinguished this from the different causation analysis used in third-party liability contexts, making clear that the efficient proximate cause doctrine is the framework for first-party property coverage disputes.

How the Predominant Cause Is Determined

Identifying the efficient proximate cause is a factual inquiry. The question is which cause was the predominant, moving force that brought about the loss — the cause that, in a natural and continuous sequence, produced the damage and set the other causes in operation. This often requires expert analysis (engineers, causation experts) to untangle how the perils interacted and which one was the true driving force. It is not simply a matter of which cause occurred first or last.

Anti-Concurrent-Causation Clauses

Insurers have responded by drafting anti-concurrent-causation (ACC) clauses, which purport to exclude a loss if an excluded peril contributed “in any sequence” with a covered peril — attempting to defeat the efficient proximate cause rule by contract. The enforceability and scope of such clauses in California is a contested and nuanced area. California law protects the efficient proximate cause doctrine where the efficient proximate cause is a covered peril, and courts scrutinize ACC language carefully; policyholders facing an ACC-based denial should not assume the clause defeats coverage without analysis.

Why It Matters

For a policyholder with a mixed-cause property loss, the efficient proximate cause doctrine can be the difference between coverage and denial. Insurers will often emphasize an excluded contributing cause; the doctrine refocuses the inquiry on the predominant cause. Establishing that a covered peril was the efficient proximate cause — through careful factual and expert development — is frequently the key to recovery.

Frequently Asked Questions

What is the efficient proximate cause doctrine?

The rule that, when a loss has concurrent covered and excluded causes, coverage is determined by the predominant (efficient proximate) cause.

What if the predominant cause is covered?

The loss is generally covered, even though an excluded peril also contributed.

What California authority governs?

Garvey v. State Farm and Insurance Code § 530.

How is the predominant cause determined?

As a factual question of which cause was the moving force that produced the loss, often requiring expert analysis.

What is an anti-concurrent-causation clause?

Policy language purporting to exclude a loss if an excluded peril contributed in any sequence — its enforceability in California is contested and should be analyzed carefully.

Does this apply to liability claims?

The doctrine as described governs first-party property coverage; causation in third-party liability is analyzed differently.

Related Personal Injury Guides

• The notice-prejudice rule
• First-party insurance bad faith
• Rescission for concealment or misrepresentation

Talk to a California Insurance Attorney

If your mixed-cause property claim was denied, the predominant cause may still be covered. Trembach Law Firm can evaluate the efficient proximate cause. Call (818) 514-7680.

Contact Trembach Law Firm at (818) 514-7680 for a confidential consultation.

Trembach Law Firm | 27001 Agoura Road, Suite 350, Calabasas, CA 91301