Additional Insured Endorsements on Liability Policies

Additional insured endorsements are among the most frequently negotiated elements of commercial liability insurance, appearing in construction contracts, commercial leases, service agreements, and vendor relationships across virtually every industry sector. These endorsements modify the named insured's policy to extend specified coverage rights to a third party — the additional insured — who then gains the ability to submit claims under that policy for covered losses. Understanding how these endorsements are structured, what protection they actually provide, and where their limits lie is essential for any party managing contractual risk transfer.

Definition and Scope

An additional insured endorsement is a formal policy modification, issued as an amendment to a general liability insurance policy, that grants a designated third party the status of an insured under that policy for specified purposes. The additional insured receives rights to coverage that the policy would otherwise reserve exclusively for the named insured.

The Insurance Services Office (ISO) — the primary standards body for commercial insurance form language in the United States — publishes standardized additional insured endorsement forms that most admitted carriers adopt or adapt. The ISO CG 20 series covers the broadest range of additional insured scenarios. Form CG 20 10 (scheduled operations), CG 20 37 (completed operations), and CG 20 26 (designated persons or organizations) represent the most commonly deployed variants (ISO, Commercial General Liability Forms).

The scope of an additional insured's coverage is not identical to that of the named insured. Key structural differences include:

Causation requirements — Most modern ISO forms limit additional insured coverage to liability "caused, in whole or in part" by the named insured's acts or omissions, not by the additional insured's own independent negligence.
Policy limit access — The additional insured shares, rather than duplicates, the named insured's policy limits. No separate limit tower exists.
Premium position — The named insured pays the premium; the additional insured pays nothing but also controls nothing about policy maintenance or renewal.
Defense rights — The additional insured may receive a defense under the insurer's duty to defend, but this right is typically scoped to the same causation threshold as indemnity coverage.

State insurance regulators — operating under frameworks set by the National Association of Insurance Commissioners (NAIC) — may impose filing requirements on non-ISO endorsement forms. In admitted markets, any deviation from approved ISO language requires a separate form filing with the state department of insurance.

How It Works

The endorsement process follows a discrete sequence from contract obligation to active coverage:

Contractual trigger — A downstream party (contractor, vendor, tenant) signs an agreement requiring it to name a specified upstream party (owner, general contractor, landlord) as an additional insured on its liability policy.
Endorsement request — The named insured contacts its broker or carrier to attach the appropriate additional insured form. In blanket endorsement structures, coverage automatically extends to any party the named insured is contractually obligated to cover, eliminating the need for a scheduled amendment each time.
Form selection — The insurer attaches the applicable ISO or manuscript endorsement. The selection of CG 20 10 (ongoing operations only) versus CG 20 37 (completed operations) versus the combined CG 20 10 + CG 20 37 package determines whether coverage extends into the post-project period — a critical distinction in construction.
Certificate issuance — A certificate of liability insurance is issued to the additional insured as evidence of coverage. The certificate itself confers no coverage rights; the endorsement does.
Claim submission — When a covered loss occurs, the additional insured submits its claim directly to the named insured's carrier, which then evaluates the claim against the endorsement's specific causation and scope language.
Primary and non-contributory language — Many contracts also require a "primary and non-contributory" clause, directing the named insured's policy to pay before any policy covering the additional insured in its own name, and without seeking contribution from those policies.

The distinction between scheduled and blanket additional insured endorsements is operationally significant. Scheduled endorsements name specific entities and require a policy amendment for each addition. Blanket endorsements — often preferred in high-volume contracting environments — cover any qualifying party automatically, reducing administrative lag.

Common Scenarios

Additional insured endorsements appear across a defined set of recurring commercial relationships:

Construction projects — General contractors routinely require subcontractors to name them as additional insureds. Project owners extend the same requirement to general contractors. This stacking structure creates layered coverage that mirrors the chain of contractual liability. Contractors' liability insurance policies are the primary vehicle.
Commercial leases — Landlords require tenants to name them as additional insureds on tenant commercial general liability policies, covering bodily injury or property damage that occurs in leased premises. Premises liability insurance considerations directly intersect with this arrangement.
Vendor and service agreements — Technology companies, consultants, and managed service providers frequently face contractual requirements to add client organizations as additional insureds. The causation-limitation language in ISO forms is particularly consequential here, since client-caused incidents may fall outside the scope of the subcontractor's policy.
Franchise relationships — Franchisors typically require franchisees to carry general liability coverage naming the franchisor as an additional insured, protecting the franchisor's brand against claims arising from franchisee operations.
Events and venues — Event producers are frequently required to name venue owners as additional insureds. Liability insurance for events and venues programs are commonly structured around this requirement.
Government contracting — Federal and state agencies contracting with private vendors routinely specify additional insured status as a contract requirement. Liability insurance for government contractors programs must accommodate these mandates.

Decision Boundaries

Several structural boundaries govern whether and how additional insured coverage applies in a given situation.

Named insured's policy must be triggered first. Additional insured coverage is derivative. If the underlying loss does not trigger the named insured's policy — because of an exclusion, a coverage gap, or a policy lapse — the additional insured's rights under that policy are extinguished. An occurrence vs. claims-made policy distinction matters here: a completed operations claim against an additional insured may fall outside the policy period under a claims-made structure if the named insured's policy has since lapsed.

The 2013 ISO revision narrowed causation language. Pre-2013 ISO forms provided additional insured coverage for liability "arising out of" the named insured's operations — a broad standard. Post-2013 ISO forms revised this to "caused, in whole or in part, by" the named insured's acts or omissions. This change excluded scenarios where the additional insured's own independent negligence was the sole proximate cause. Contracts executed under pre-2013 certificates may have broader coverage expectations than the current policy language supports.

Anti-indemnity statutes constrain scope in construction. More than 40 states have enacted anti-indemnity statutes limiting or voiding contractual indemnification clauses that attempt to hold a party harmless for its own negligence. These statutes interact directly with additional insured requirements. In states such as California (California Civil Code § 2782), Texas (Texas Insurance Code § 151.102), and New York, courts have held that additional insured endorsements purporting to cover the additional insured's sole negligence may be unenforceable as violations of applicable anti-indemnity law.

Excess and umbrella layers require separate endorsements. A named insured's umbrella liability insurance or excess liability insurance policy does not automatically follow-form to extend additional insured coverage established at the primary layer. Each layer requires its own additional insured endorsement if the contract requires coverage in excess of primary limits.

Certificates of insurance are not substitutes for endorsements. The ACORD 25 certificate form — the standard evidence-of-insurance document — carries a disclaimer stating explicitly that it confers no coverage and does not amend the policy. Reliance on a certificate alone, without confirming the underlying endorsement is attached, represents a material gap in risk management. Liability insurance exclusions and endorsement gaps discovered at the time of claim cannot be retroactively corrected.

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