What Is An Additional Insured Endorsement? A Plain-English Guide
How additional-insured status works on a sub's COI, which forms grant it, and what to verify.
What it actually does
An additional-insured (AI) endorsement adds a party — usually the general contractor or owner — to a subcontractor's liability policy, so that the sub's insurer also defends and indemnifies that party for claims connected to the sub's work. It's the mechanism that pushes the risk of a sub's work onto the sub's own insurance, where it belongs, instead of onto the GC's policy.
In construction, AI status is granted by specific ISO forms. The scheduled forms (CG 20 10 for ongoing operations, CG 20 37 for completed operations) name each protected party. The automatic forms (CG 20 33 for ongoing, CG 20 38 for both) grant status to anyone a written contract requires. A complete AI requirement covers BOTH ongoing and completed operations — most defect claims arrive after the work is finished — and is paired with a primary-and-noncontributory endorsement (CG 20 01) and waivers of subrogation.
The most common verification failures: relying on the COI's "additional insured" checkbox instead of the actual endorsement; accepting ongoing-operations coverage only; and assuming umbrella limits extend AI status when the umbrella doesn't follow form.
Verification checklist
- 01Require the actual AI endorsement, not just a checked COI box.
- 02Confirm BOTH ongoing (CG 20 10/20 33) and completed operations (CG 20 37/20 38) are covered.
- 03Confirm primary & noncontributory (CG 20 01) and waivers are present if the contract requires them.
- 04Check whether AI status extends to the umbrella (follow-form).
Common mistakes
- ·Relying on the COI checkbox rather than the issued endorsement.
- ·Accepting ongoing-operations AI status only and missing completed operations.
- ·Assuming umbrella limits carry the AI status without confirming follow-form.
Frequently asked questions
What does it mean to be an additional insured?
It means a subcontractor's liability policy is endorsed to also cover you (the GC/owner) for claims connected to the sub's work, so the sub's insurer responds rather than yours.
Which forms grant additional-insured status?
CG 20 10 (ongoing) and CG 20 37 (completed) are scheduled; CG 20 33 (ongoing) and CG 20 38 (both) are automatic. A full requirement covers ongoing and completed operations.
Is the additional-insured box on a COI enough?
No. The box is informational. You need the actual endorsement attached, naming you (scheduled) or triggered by your written contract (automatic).
Checking a sub's COI right now?
Upload it free — we'll check every endorsement, edition, and limit against your requirements and hand back a per-vendor gap report.
Run a free COI audit →Related endorsements
This page explains Additional Insured (Explained) in plain English for COI verification. It is informational only and is not legal or insurance advice — confirm the actual endorsement language and have your counsel or insurance agent review your specific requirements.