Blanket Additional Insured: Definition and How It Works

A blanket additional insured endorsement is a policy provision that automatically extends additional insured status to any party that the named insured is contractually required to add — without requiring that each party be individually scheduled and named on the policy. Under a blanket endorsement, coverage attaches to an upstream party (general contractor, property owner, developer, or other indemnitee) the moment a written contract requires it, rather than requiring a separate endorsement or certificate for each project. The most widely used blanket form is ISO CG 20 33 (additional insured for owners, lessees, or contractors — automatic status when required by written contract), though insurers use proprietary wording that may be broader or narrower.

Blanket vs. Scheduled Additional Insured

The trade-off: blanket endorsements are administratively efficient but rely entirely on the underlying written contract to define who qualifies. If a subcontractor begins work before a written contract is signed, no blanket additional insured protection exists for the upstream party — a common cause of coverage gaps discovered at claim time.

What the Written Contract Requirement Means

ISO CG 20 33 and most proprietary blanket forms require that the additional insured status be triggered by a written contract or agreement executed before the occurrence that gives rise to a claim. "Written" is strictly interpreted — verbal agreements, emails alone, or unsigned drafts typically do not satisfy the trigger. The contract must also require that the named insured add the other party as an additional insured on the CGL policy specifically; a general indemnification clause without an explicit insurance requirement is usually insufficient.

In practice, this means:

• A subcontractor's blanket endorsement covers the general contractor only if the executed subcontract agreement contains a written requirement for additional insured status.
• If work begins before the subcontract is signed — a common occurrence in fast-moving construction — the GC is not protected under the blanket endorsement for occurrences during that gap.
• If the contract specifies a particular ISO form number (e.g., "CG 20 10 04 13"), the blanket endorsement may not satisfy the requirement if the insurer uses a different form; the COI and policy must be reviewed together.

Scope of Coverage Under a Blanket Endorsement

Blanket additional insured status does not give the additional insured the same rights as the named insured. Coverage is typically limited to liability arising out of the named insured's operations — the additional insured's own independent negligence is generally not covered. Courts in most states apply the anti-indemnity statute framework and read policy language narrowly: if the injury was caused solely by the additional insured's own negligence, the blanket endorsement provides no coverage.

Key coverage scope questions to verify for a client's blanket endorsement:

• Does the endorsement cover completed operations in addition to ongoing operations? (ISO CG 20 37 adds completed operations coverage; CG 20 33 alone does not in all versions.)
• Is there a primary and non-contributory provision? Many contracts require the subcontractor's policy to be primary and not seek contribution from the GC's policy. Verify the blanket endorsement includes this language or that a separate primary/non-contributory endorsement is attached.
• Does the endorsement include waiver of subrogation? A blanket waiver of subrogation (ISO CG 24 04) is typically required alongside blanket additional insured status in standard construction contracts.

Related Terms

• Additional Insured — the foundational concept; blanket additional insured is the delivery mechanism for extending this status automatically across multiple contracts
• Certificate of Insurance — the document used to evidence blanket additional insured status; must accurately reflect the endorsement form and scope
• Waiver of Subrogation — frequently required alongside blanket AI status in construction contracts; prevents the insurer from pursuing the additional insured after paying a covered claim
• Commercial General Liability — the policy type to which blanket additional insured endorsements are most commonly attached
• Errors and Omissions Insurance — brokers who fail to secure proper blanket AI coverage or advise clients that a blanket endorsement satisfies a scheduled-form requirement face professional liability exposure

How Insurance Brokers Use This in Practice

Blanket additional insured endorsements are standard in construction, real estate, and vendor-managed service agreements, but they are also among the most frequently misunderstood coverage provisions at claim time. Brokers should address three areas proactively:

At submission and binding: Confirm the insurer's blanket AI endorsement form. Compare the wording to the specific contractual requirement. If the contract specifies a named ISO form, verify the insurer's proprietary form is substantively equivalent — many are not. Document this analysis in the client file.

At certificate issuance: A COI that simply says "additional insured as required by written contract" is sufficient in most jurisdictions, but some upstream parties require the specific endorsement form number listed on the certificate. Train clients and their administrative staff not to issue COIs that overstate or misrepresent coverage scope — this creates E&O exposure for both the broker and the named insured.

At renewal: Blanket endorsements are policy-level provisions; confirm they carry forward on renewal. Carrier changes or endorsement form updates can alter the scope of blanket AI protection without triggering an obvious coverage change notice. A mid-term carrier swap that substitutes a narrower proprietary form for the prior ISO form is a known source of coverage gaps.