Additional Insured Endorsement Explained: What Every GC Needs to Know

TL;DR: An Additional Insured (AI) endorsement extends a subcontractor's GL policy to cover the GC for vicarious liability, but the COI box alone proves nothing without the actual endorsement form on file. Demand both CG 20 10 (ongoing operations) and CG 20 37 (completed operations) by form number, not just a producer's note.

If your subcontractor agreement has ever said "Contractor shall be named as Additional Insured on Subcontractor's Commercial General Liability policy," and you assumed that was handled, this post is for you.

The Additional Insured endorsement is the single most misunderstood piece of subcontractor insurance, and most of the GCs who think they're protected as AI are actually exposed. This guide covers what it does, how it works, the specific forms to look for, and how to verify you're actually covered.

What Is an Additional Insured Endorsement?

An Additional Insured (AI) endorsement is an amendment to an insurance policy that extends coverage to another party who is not the named insured but needs the same protection for a specific reason.

In construction, the reason is vicarious liability. If your subcontractor's worker drops a tool and injures someone, the injured party will typically sue:

1. The sub who dropped the tool
2. The subcontractor's employer
3. You, the GC, for hiring them

Without an AI endorsement, you're defending yourself with your own insurance. With an AI endorsement, the sub's policy steps in to defend you as if you were named on the policy. Your insurance stays uninvolved (ideally), your premium doesn't take a hit, and the sub's carrier (whose insured actually caused the problem) handles the claim.

This is why Additional Insured language is so critical in every subcontractor agreement. It's not a formality. It's the mechanism that transfers risk where it belongs.

The Problem: AI Status Doesn't Exist on the COI Alone

Here's where most GCs get caught. When you receive a Certificate of Insurance and the Description of Operations box says "[GC Name] is named as Additional Insured," that is just a statement written by the producer on a one-page form. It does not, by itself, make you an Additional Insured.

You are only actually an Additional Insured if the sub's policy has a matching endorsement attached to it: a separate document, usually a one- or two-page form, filed with the insurer and referenced by a specific form number.

The COI is a summary. The endorsement is the real document. If the COI says you're AI but no endorsement exists, you have nothing. A claim will expose this gap instantly.

The Two Forms That Matter: CG 20 10 vs CG 20 37

The two most common Additional Insured endorsements for construction are both ISO (Insurance Services Office) forms, and they cover different things. You need both, not one or the other.

CG 20 10: Ongoing Operations

CG 20 10 ("Additional Insured, Owners, Lessees or Contractors, Scheduled Person or Organization") provides AI coverage for bodily injury, property damage, or personal/advertising injury caused in whole or in part by the sub's ongoing operations.

Translation: while work is actively happening on site, CG 20 10 covers you as Additional Insured.

What it doesn't cover: anything that happens after the sub finishes their work. That gap is covered by CG 20 37.

CG 20 37: Completed Operations

CG 20 37 ("Additional Insured, Owners, Lessees or Contractors, Completed Operations") extends AI status to cover claims arising from the sub's completed work, after the job is done.

This is massive for construction. Most construction defect claims (water intrusion, structural failures, faulty installations) don't show up until months or years after the work is finished. Without CG 20 37, those claims are not covered under the sub's policy, and you're defending them with your own insurance.

Why You Need Both

GCs who only get CG 20 10 are protected during the project and completely exposed afterward. Given that construction defect claims in many states have a 6 to 10 year statute of repose, the "after the project" window is where the real risk lives. Contract language should always require both forms, and the COI should reference both.

"Blanket" Additional Insured Endorsements

Some sub insurers issue "blanket" AI endorsements: forms that automatically extend AI status to anyone the named insured is required by written contract to add as Additional Insured. Blanket forms are fine; they just mean you don't need to be individually scheduled on the policy.

The key thing with blanket forms: there must be a written contract between you and the sub that requires AI status. Without a written contract requirement, the blanket endorsement doesn't apply to you. This is why your subcontractor agreement must explicitly require AI status rather than just reference it verbally.

Primary vs Non-Contributory Coverage

Getting named as Additional Insured is only half the battle. The other half is making sure the sub's coverage pays first, before your own policy gets tapped.

By default, when two policies both cover the same loss, they share. Your carrier pays a portion, the sub's carrier pays a portion, and both carriers' loss histories get affected. You don't want this.

"Primary and Non-Contributory" language tells the sub's insurer that their coverage pays first, in full, and your insurance is not required to contribute. This language must be:

1. In your subcontract (required of the sub)
2. On the CG 20 10 / CG 20 37 endorsements (or via a separate Primary/Non-Contributory endorsement like CG 20 01)
3. Referenced on the COI in the Description of Operations

Without all three, you may end up sharing a loss with the sub's insurer even though they caused it.

How to Verify You're Actually Additional Insured

The short answer: don't trust the COI. Verify the endorsement.

Here's the process:

1. Receive the COI. Check that Description of Operations references CG 20 10 and CG 20 37 and Primary and Non-Contributory language.
2. Request the actual endorsements. Ask the sub (or their producer) to email you copies of the CG 20 10 and CG 20 37 endorsement pages attached to the policy. This should be a normal, routine request. Any producer or agent familiar with construction should send them same-day.
3. Verify the endorsement language. Confirm the form numbers match, your company is listed or a blanket provision applies, and there's no exclusionary language limiting the coverage.
4. File everything. Store the COI and both endorsement pages together in the sub's compliance file. If a claim ever happens, these are the documents that prove you're covered.

This feels like overkill until you've had a claim where the sub's insurer denied AI status because the endorsement didn't exist. Then it feels like the most important thing you do all week.

Common AI Mistakes GCs Make

1. Accepting the COI as proof. A COI is a summary. Without the actual endorsement, you have nothing.
2. Only getting CG 20 10, not CG 20 37. Ongoing-ops coverage evaporates the minute the sub completes their work. Completed-ops coverage is what protects you for the long tail of defect claims.
3. Missing Primary and Non-Contributory language. Without it, your insurance shares a loss the sub caused.
4. Not keeping endorsements on file. When a claim happens 18 months later, you need to be able to produce the endorsement that was active when the work was performed.
5. Not tracking expiration. When the sub's policy renews, the endorsement renews too, unless the sub switched carriers, changed coverage, or let something lapse. Every renewal is a fresh verification job.

How PaperBoss Helps with AI Verification

PaperBoss is certificate-of-insurance tracking software built for GCs. For every COI you collect, PaperBoss surfaces an Additional Insured checklist: did the sub provide the CG 20 10? The CG 20 37? Is Primary and Non-Contributory language present? Are the policy dates current?

You upload each certificate and its endorsement pages once, and PaperBoss keeps them organized and flags gaps before they become claims. When the policy expires, you get automated reminders to re-verify the endorsements on the renewal, and when an auditor or owner asks for proof that a sub was AI on a given date, you can pull the full documentation in seconds.

Start a 14-day free trial, no credit card required.

Frequently Asked Questions

What's the difference between Additional Insured and Certificate Holder?

A Certificate Holder is essentially a mailing address, a party who received the COI. Being a certificate holder confers no coverage. An Additional Insured is a party actually covered under the policy via endorsement. You want to be both, but only AI status matters for protection.

Is Additional Insured status automatic if my contract requires it?

Not unless the sub's policy has a blanket AI endorsement that applies via written contract. Even with a blanket endorsement, you should verify the endorsement is in place and the language applies to you.

Can a sub charge me extra for Additional Insured coverage?

Some sub policies do carry an AI premium, and subs may pass it through. This is legitimate but usually minor (often $50 to $500 per certificate). Budget for it. Refusing to pay means the sub isn't covered the way your contract requires.

Does Additional Insured coverage apply to sole negligence of the GC?

Generally no. Most modern AI endorsements (CG 20 10 10 01 and later) only cover injury caused "in whole or in part" by the sub's acts or omissions. If the claim is 100% your fault, the sub's policy typically won't cover it. This is why your own General Liability policy still matters: AI is additional protection, not a substitute.

How often should I verify AI endorsements?

At minimum, every policy renewal. More rigorously, at the start of every new project and any time the sub's coverage changes. PaperBoss automates the reminder cycle so you don't have to track it manually.

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This article is for educational purposes only and does not constitute legal or insurance advice. Consult a licensed construction insurance broker for guidance on your specific situation.