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Additional Insured Endorsements: CG 20 10, CG 20 37, and Blanket Forms Explained

By SubCover HQ · Updated Oct 29, 2026 · 3 min read

Your contract says the sub must name you as an additional insured. The certificate comes back with "AI: Y" checked. Are you covered? That depends on which endorsement the policy actually has. Here's a plain-English tour of the forms you'll see most often on contractor general liability policies.

Why the endorsement matters more than the certificate

A certificate of insurance only summarizes coverage. Additional insured status is created by an endorsement attached to the sub's general liability policy, and the endorsement's wording decides who's covered, for what, and for how long. Two subs can both show "ADDL INSD: Y" on their ACORD 25 and give you very different protection. That's why many contracts require a copy of the endorsement, not just the certificate. (For the basics, see additional insured vs. certificate holder.)

Ongoing vs. completed operations

The single most important distinction is timing:

• Ongoing operations covers claims arising while the sub is still performing work on the job.
• Completed operations covers claims that arise after the work is finished, such as a leak from a roof installed last year or a fire traced to wiring after turnover.

Construction defect and injury claims often surface after a project is done. An endorsement that only covers ongoing operations can leave the GC or owner with no additional insured protection for exactly those claims.

The common ISO forms

Many insurers use standard forms published by ISO (Insurance Services Office), identified by a form number and an edition date. Insurers also write their own versions, so always read the actual wording.

CG 20 10: Owners, Lessees or Contractors, Scheduled Person or Organization

Adds the person or organization named in its schedule as an additional insured for ongoing operations performed for them. Older editions (notably the 11 85 edition) also reached completed work, which is why some contracts still ask for "CG 20 10 11 85 or equivalent." Current editions limit coverage to ongoing operations, so they're usually paired with a completed operations form.

CG 20 37: Owners, Lessees or Contractors, Completed Operations

The companion form that extends additional insured status to completed operations for the scheduled party. When a contract asks for "CG 20 10 and CG 20 37 or equivalent," this pairing is what it means.

Blanket (automatic) additional insured forms

Instead of naming each party, blanket forms make anyone an additional insured when the named insured agreed to it in a written contract. Examples include CG 20 38 and CG 20 33 for ongoing operations and CG 20 39 for completed operations. Blanket forms are convenient for subs who work for many GCs and property managers, but check two things:

• Who qualifies. Some blanket forms only cover the party the sub contracted with directly. If the owner and the GC both need coverage, the endorsement has to reach parties above the direct contract, and the subcontract has to require it.
• Timing of the contract. Blanket forms usually require the written contract to be signed before the injury or damage happens. A handshake deal or a contract signed after the fact may not trigger coverage.

The limits written into newer editions

Since the 2013 editions, the standard ISO forms say additional insured coverage applies only to the extent permitted by law, and no broader than what the contract requires. In practice, your contract wording now does more of the work: if it doesn't clearly require completed operations coverage, primary and noncontributory wording, or specific limits, you may not get them. See primary and noncontributory explained.

What to ask the sub's agent for

• A current ACORD 25 with ADDL INSD marked on the general liability line (and on auto and umbrella if your contract requires it).
• Copies of the actual additional insured endorsements, both ongoing and completed operations, with form numbers and edition dates.
• Confirmation that blanket forms cover your entity and any upstream parties your contract names.
• Completed operations coverage that lasts as long as your contract requires after the job ends, often several years.

Red flags

• "Additional insured" typed in the description box with no endorsement to back it up.
• Only an ongoing operations form when your contract requires completed operations.
• Endorsements that name a different entity than the one in your contract.
• Exclusions for the type of work the sub is doing, such as residential or roofing, buried in other endorsements.

Checking endorsements on every certificate is tedious, which is why it's often skipped. Use the free COI compliance checker to list gaps and draft a deficiency email, or let SubCover HQ collect certificates and endorsements and flag what's missing for you.

This guide is general information, not insurance or legal advice. ISO, CG form numbers, and ACORD are trademarks of their respective owners; SubCover HQ is not affiliated with them. Your contracts, insurance professional, and attorney determine what you should require.