ISO Commercial Liability Umbrella Form (CU 00 01): Limits and Drop-Down

The ISO commercial liability umbrella form CU 00 01 is the standardized contract that sits above your business’s primary liability policies and pays covered claims once those underlying limits are used up. Published by the Insurance Services Office, it gives carriers across the country a common structure, so the umbrella a business buys in one state reads substantially the same as one bought elsewhere. The form has two insuring agreements, its own set of exclusions, and conditions that put real obligations on you throughout the policy period. Understanding how those pieces interact is the difference between an umbrella that responds the way you expected and one that leaves you holding a seven-figure gap.

What Coverage A and Coverage B Pay For

Coverage A handles bodily injury and property damage liability. When someone is hurt or property is damaged because of an occurrence covered by both the umbrella and an underlying primary policy, the primary pays first. Once that underlying limit is exhausted, Coverage A pays the rest of the ultimate net loss up to the umbrella’s own limit. The insurer also has the right and duty to defend you against any covered suit once the underlying insurance has been exhausted or does not provide coverage for the claim.¹

Coverage B picks up personal and advertising injury: false arrest, malicious prosecution, libel, slander, invasion of privacy, and infringement of another’s copyright or advertising idea.² The insurer pays the ultimate net loss above the retained limit here too, with the same defense duty once underlying insurance is exhausted or does not apply. The practical difference is that some personal and advertising injury claims fall outside the scope of underlying policies entirely. That is where the self-insured retention does the work.

How the Limits Fit Together

Your declarations page shows two headline numbers. The each-occurrence limit caps what the insurer pays for all bodily injury and property damage from a single event under Coverage A. The general aggregate limit is the ceiling on everything the insurer pays during the policy period for Coverage A claims (other than those arising out of a covered auto) combined with all Coverage B claims.¹ A separate personal and advertising injury limit under Coverage B caps the total payout for all such injury to any one person or organization. On a multi-year policy the aggregate resets at the start of each consecutive annual period rather than pooling across the term.

The Retained Limit and Self-Insured Retention

The retained limit is the amount you absorb before the umbrella responds. When an underlying primary policy covers the claim, the retained limit equals whatever that underlying policy pays. When no underlying policy applies to the loss at all, the retained limit becomes the self-insured retention listed in your declarations, and you pay that SIR out of pocket before the umbrella insurer owes anything for the claim or the defense.³

SIRs of $10,000 to $25,000 are the most common range for mid-market commercial accounts, and carriers may require a higher retention when the exposure not covered by underlying insurance is substantial.⁴ The SIR is not a deductible. A deductible reduces the total limit available; an SIR sits below the limit, leaving the full umbrella limit intact above it.

Ultimate Net Loss

The umbrella insurer’s payment obligation is measured by the “ultimate net loss,” defined as the total amount you become legally obligated to pay as damages through a settlement, judgment, or approved alternative dispute resolution, minus any recoveries or salvages collected.⁵ If a jury awards $3 million, you recover $200,000 through subrogation, and the underlying policy paid its $1 million limit, the umbrella’s ultimate net loss is $1.8 million. Defense costs the insurer incurs on your behalf do not erode policy limits; they are handled as supplementary payments outside the limits of insurance.

Who Counts as an Insured

The named insured on the declarations page carries the broadest rights and the deepest obligations. Coverage then extends to several categories of people acting in a business capacity:

Officers, directors, and stockholders, while performing duties related to the named insured’s business.
Employees and volunteer workers, for acts within the scope of their employment or assigned duties.
Newly acquired or formed organizations, automatically covered for a limited window (often 90 days or until the end of the policy period, whichever comes first). After that window closes, the entity needs to be scheduled onto the policy.⁶

One line that trips up policyholders is the one between autos and mobile equipment. The CGL underlying policy generally covers liability arising from mobile equipment such as forklifts, cranes, or on-site bulldozers, but it excludes autos, which need a separate business auto policy.⁷ If a piece of equipment that straddles the definition sits under the wrong underlying policy, the umbrella may not respond as expected because the underlying coverage was never properly in place.

Where Coverage Applies

The CU 00 01 provides worldwide coverage with one carve-out: any country or jurisdiction subject to U.S. trade sanctions or embargoes is excluded.¹ For suits brought outside the United States, its territories, Puerto Rico, or Canada, if local law prevents the insurer from directly defending or paying on your behalf, you handle the defense and the insurer reimburses reasonable expenses. Any coverage dispute between you and the insurer must be filed in the courts of the United States, its territories, Puerto Rico, or Canada, regardless of where the underlying incident happened.

What the Form Will Not Pay For

The CU 00 01 excludes several broad categories of risk that require their own specialized coverage:

Expected or intended injury. Deliberate acts of harm are not insurable under the umbrella.
Contractual liability, except for “insured contracts” like certain lease agreements and sidetrack agreements.
Liquor liability. Businesses that manufacture, distribute, sell, or serve alcohol face a blanket exclusion and need a separate liquor liability policy.
Workers’ compensation and similar statutory obligations.
Pollution. The discharge, dispersal, or release of pollutants is excluded broadly, and businesses with environmental exposure need standalone pollution liability.
Employer’s liability for bodily injury to employees arising out of and in the course of employment, beyond what the underlying employer’s liability coverage handles.

These mirror what you find in most primary CGL policies, and that is deliberate. The umbrella sits above the primary layer for covered claims; it does not fill every gap the primary intentionally leaves open.

The Underlying Insurance Trap

The form imposes a strict duty to keep every scheduled underlying policy in force at the limits listed in the Schedule of Underlying Insurance. If a primary policy lapses, is canceled, or has its limits reduced below the scheduled amount, the umbrella insurer does not step in to fill the gap. The insurer calculates its payment as though the underlying coverage were still in place at the original limits, and you absorb the difference.⁸

The math is painful. Suppose the schedule requires $1 million in underlying CGL coverage, the policy has lapsed, and a $2 million claim hits. The umbrella insurer treats the first $1 million as your problem and pays only the excess above that phantom limit. You are out $1 million because of an administrative failure, not because of any coverage limitation in the umbrella itself.

Drop-Down When the Underlying Aggregate Exhausts

A different situation arises when the underlying policy stays in force but its aggregate limit is eaten up by earlier claims during the same policy period. Many umbrella forms include a drop-down provision that lets the umbrella respond once the underlying aggregate is reduced or exhausted, effectively stepping into the primary policy’s position for subsequent claims.⁹ When the umbrella drops down, it may maintain its own terms rather than adopting the underlying policy’s. The self-insured retention is sometimes waived in this scenario, though that varies by carrier.¹⁰

What You Must Do After a Claim

The conditions section spells out exactly what the insured must do when something goes wrong. These are not suggestions. Failing to follow them can result in a denied claim.

Report the occurrence promptly. Notify the insurer as soon as practicable of any occurrence or offense that might result in a claim, no matter how minor it looks. Include how, when, and where it happened, plus the names and addresses of injured parties and witnesses.
Record and forward suit papers immediately. If a claim or suit arrives, record the details and the date received, then send copies of all demands, notices, summonses, and legal papers to the insurer without delay.
Cooperate fully. Authorize the insurer to access records, assist in investigations, and help enforce rights against third parties who may share liability.
Do not volunteer payments. No insured may make voluntary payments, assume obligations, or incur expenses beyond first aid without the insurer’s consent. Paying at your own cost is permitted; the umbrella will not reimburse unauthorized settlements.

The form also bars anyone from joining the insurer as a party to a lawsuit against the insured, or suing the insurer directly, until every term of the policy has been fully satisfied.

Endorsements That Reshape the Form

The base CU 00 01 is rarely issued without endorsements tailoring it to the policyholder’s industry and risk profile. A few carry particular weight:

CU 04 02 (Electronic Data Liability) adds coverage for third-party claims involving property damage to electronically stored data, with a sub-limit inside the umbrella’s per-occurrence limit.¹¹
CU 21 86 and CU 21 87 are mandatory cyber and data exclusions that remove damages from disclosure of confidential or personal information and data-related liability. CU 21 86 preserves a limited exception for bodily injury; CU 21 87 removes even that exception.¹¹
Additional insured and leased-worker endorsements adjust who is covered and under what conditions.

Businesses with cyber exposure should look closely at whether their umbrella carries CU 21 86 or CU 21 87, because the base form’s coverage for data-related claims is effectively gutted by either one. A standalone cyber liability policy fills that gap.

Umbrella vs. Excess Liability

The two terms get used interchangeably in casual conversation, but they describe different products. An umbrella like the CU 00 01 broadens coverage beyond what the underlying policies provide, picking up certain claims the primary excludes entirely, subject to the SIR. An excess liability policy follows form to the underlying: same terms, same exclusions, just higher limits.¹² If the underlying CGL excludes a particular claim, the excess policy excludes it too. The umbrella might still cover it under its own broader terms, minus the SIR.

Excess policies give more predictability because the coverage mirrors the primary layer. Umbrellas offer wider reach but demand closer attention to the form’s own exclusions and conditions, since they operate under independent language rather than deferring to the primary.¹³ For businesses with unusual exposures that primary policies tend to exclude, the umbrella’s broader reach is the whole point.

1
Guard Insurance Group. Commercial Liability Umbrella Coverage Form
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WBASNY. Commercial Liability Umbrella Declarations
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IRMI. Self-Insured Retention (SIR)
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Rough Notes. Commercial Umbrella Liability Insurance
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MyNewMarkets. The Difference Between Umbrella and Excess Liability Coverage
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IRMI. Newly Acquired Entities
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IRMI. Auto Versus Mobile Equipment in the CGL
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InsuranceXDate. Form CU 00 01: Commercial Liability Umbrella Coverage Form
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IRMI. Drop Down Provision
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Rough Notes. Excess Versus Umbrella Liability: Understanding the Differences
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RNC-Pro. ISO Commercial Liability Umbrella Coverage Form
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Alliant Insurance Services. Exploring Secondary Coverage: Distinguishing Between Commercial Excess Liability and Umbrella Insurance Coverage
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IRMI. Commercial Umbrella Policy — A Few Things To Consider