What Is an Additional Insured Endorsement (and Why GCs Must Verify It)

A general contractor asks a subcontractor for insurance. The sub emails back a certificate of insurance (COI) with the GC's name typed into the box labeled "additional insured." Everyone moves on. Months later, a claim arises from the sub's work—and the GC discovers the hard way that the certificate never actually gave them coverage.

This scenario is common, avoidable, and rooted in one misunderstanding: a certificate of insurance does not make you an additional insured. The endorsement does. If you're a GC relying on subcontractor policies to protect you, this distinction is one of the most important things you can understand.

This is general information, not legal or insurance advice.

The Certificate Is a Summary, Not a Contract

A COI is a snapshot. It's a one-page form—usually the ACORD 25—that summarizes what policies a subcontractor claims to carry: general liability limits, dates, the insurer's name. It's issued by an insurance agent as a courtesy.

Read the fine print on the certificate itself and you'll see language stating that it confers no rights on the holder and does not amend, extend, or alter the coverage of the underlying policy. In other words, the certificate is a description of insurance, not the insurance. Typing your company name into the "additional insured" field on a COI has roughly the same legal effect as writing it on a napkin. It signals intent, but it doesn't grant coverage.

Coverage lives in the policy. And the only way to actually add your company to a subcontractor's general liability policy is through an endorsement—an official document, issued by the insurer, that amends the policy to include you as an additional insured.

What an Additional Insured Endorsement Actually Does

When you're named as an additional insured on a subcontractor's general liability policy, you gain the ability to seek coverage under their policy for claims arising out of their work. This matters because in construction, a GC can be pulled into a lawsuit over an incident caused entirely by a sub. Additional insured status is designed so that the party responsible for the work—and their insurer—responds to that claim, rather than the GC's own policy taking the first hit.

The endorsement is a named form, typically from the Insurance Services Office (ISO) family of forms. It has a form number and an edition date. It attaches to the policy and spells out exactly who is covered, for what, and under what conditions. This is the document you actually need—not just the certificate that references it.

CG 20 10 vs. CG 20 37: Why the Form Number Matters

Two ISO endorsement forms come up constantly in GC-subcontractor relationships, and the difference between them is not trivial.

• CG 20 10 — Additional Insured – Owners, Lessees or Contractors – Scheduled Person or Organization. This form grants additional insured status for liability arising out of the named insured's (the sub's) ongoing operations. The key limitation: many editions of this form are commonly understood to cover ongoing work, but not necessarily liability that shows up after the sub has finished—the completed-operations phase.

• CG 20 37 — Additional Insured – Owners, Lessees or Contractors – Completed Operations. This form extends additional insured status to claims arising out of the sub's work after it's completed—the products-completed operations hazard.

Why does this matter to a GC? Construction defects and injuries often surface after a project is finished. If a sub's work fails a year later and you're only named on a CG 20 10, you may not have the completed-operations protection you assumed you had. That's why many GCs require both forms—ongoing operations and completed operations—so coverage follows the work through its full life.

Edition dates matter too. ISO periodically revises these forms, and different editions can define the scope of coverage differently—including whether coverage is tied to a written contract, and how it interacts with your own policy. Two certificates can both say "CG 20 10" and still behave differently depending on the edition year.

None of this is visible on a plain certificate. The COI might list a form number if you're lucky, but it won't show you the actual endorsement language. This is general information, not legal or insurance advice—when the stakes are high, have your broker or counsel review the actual forms.

How to Verify Additional Insured Status: A GC Checklist

Don't accept a certificate at face value. Verify. Here's a practical sequence:

1. Require the endorsement, not just the COI. Ask for a copy of the actual additional insured endorsement attached to the sub's policy. If they can only produce a certificate, you don't yet have proof of coverage.
2. Match the named insured and your entity. Confirm the sub's legal name on the endorsement matches the entity you contracted with, and that your company is correctly named or covered under a blanket endorsement.
3. Check the form number and edition date. Confirm you're getting the forms your contract requires—commonly both CG 20 10 (ongoing operations) and CG 20 37 (completed operations)—and note the edition year.
4. Confirm the policy dates cover your project. Additional insured status is only useful if the policy is in force during—and, for completed operations, after—the work.
5. Read the coverage triggers and limitations. Some endorsements only apply when a written contract requires additional insured status, so make sure your subcontract agreement actually contains that requirement.
6. Watch the "primary and non-contributory" question. Whether the sub's coverage responds before yours is often governed by separate policy language. Confirm your contract and the endorsement align on this.
7. Re-verify at renewal. Policies renew, forms change, and coverage can lapse. A certificate that was valid at bid time may be worthless by the time a claim hits.

The recurring theme: the certificate points at coverage, but the endorsement is the coverage. Verify the source document.

Why This Gets Missed—and How to Stay Ahead

Most COI problems aren't fraud. They're volume. A GC managing dozens of subs across multiple active jobs is tracking hundreds of certificates, endorsements, expiration dates, and renewal cycles—usually in a spreadsheet or a filing cabinet. It's easy to file a certificate, assume the endorsement behind it is correct, and never look again.

That gap is exactly where risk hides. Purpose-built COI tracking software helps you request the right forms, store the actual endorsements alongside the certificates, flag missing completed-operations coverage, and get alerted before a policy lapses—so verification becomes a routine step instead of a scramble after a claim.

If you'd like to see how that works on your own subcontractor list, TradeGuard offers a free 14-day trial. It's a low-pressure way to find out what your certificates are—and aren't—actually telling you.