🎯 An additional insured endorsement on a general liability policy is a form added to a subcontractor's GL policy that extends the policy's protection to a named third party, usually the general contractor, for liability arising out of the subcontractor's work. The endorsement is the actual coverage; the certificate of insurance (COI) only announces that coverage exists. The two forms a GC commonly demands are CG 20 10 (ongoing operations) and CG 20 37 (completed operations), and without both on the policy, the "additional insured" line on your COI may not protect the GC at all.
Last updated: October 2026.
TL;DR
- An additional insured endorsement adds a third party (the GC) to your GL policy so your insurer defends and pays on their behalf for claims arising from your work.
- CG 20 10 covers ongoing operations; CG 20 37 covers completed operations after you leave the site. Many commercial subcontracts require both.
- Additional insured vs named insured: the named insured owns the policy; an additional insured borrows its protection for specific exposures only.
- A COI is not proof of the endorsement. Ask for the endorsement forms themselves, every renewal, no exceptions.
Definition: what an additional insured endorsement actually is
An additional insured endorsement is a written form issued by your insurer that attaches to your commercial general liability (CGL) policy and extends that policy's coverage to a party you did not originally buy it for. In construction, that party is the general contractor, construction manager, or owner who hired you.
The endorsement changes who your policy protects. Instead of defending only you, your insurer now also defends and indemnifies the additional insured for claims that "arise out of" your ongoing or completed work. That is the whole mechanic. These clause mechanics come from standard ISO forms, so what "additional insured" means generally does not change whether you are in Texas, Ohio, or California.
Additional insured vs named insured: what is the difference?
The named insured owns the policy, pays the premium, and is covered for the full scope of the policy. An additional insured is added by endorsement and is covered only for liability tied to your work, nothing broader.
Here is the practical split:
| Named insured | Additional insured | |
|---|---|---|
| Owns the policy | Yes | No |
| Pays premium | Yes | No |
| Scope of coverage | Full policy | Only liability arising out of your work |
| Can file its own claims freely | Yes | Only for covered scope |
| Appears on | Declarations page | Endorsement form (CG 20 10 / CG 20 37) |
| Receives cancellation notice | Yes | Only if endorsed |
When a GC says "name us as additional insured," they are asking to borrow your policy's defense for anything your crew causes on their job. They are not becoming a named insured, and they do not get your full policy limits for their own unrelated exposures.
How additional insured works on GL in the real world
Here is how additional insured works on GL, step by step, from the moment the paperwork lands:
- The subcontract's insurance exhibit requires you to name the GC as additional insured, often with specific form numbers written in.
- Your agent endorses your GL policy with CG 20 10, CG 20 37, or a blanket form that captures "any party you are required by written contract to add."
- Your insurer issues the endorsement as a separate document that physically attaches to the policy.
- The COI is generated showing the GC as certificate holder and referencing additional insured status.
- A claim arises from your work. The GC tenders the claim to your insurer. If the endorsement is on file, your insurer defends them. If only the COI exists, there is nothing to tender against.
That fifth step is where contractors get burned. A broker can type "additional insured" on a COI in thirty seconds. That line is a statement about intent, not a grant of coverage. We break the full mechanic down in the difference between a certificate of insurance and an endorsement, because this single gap causes more withheld payments than any other item on an exhibit.
CG 20 10 vs CG 20 37: which form does the GC want?
The GC usually wants both, and here is why.
| Form | Covers | When it applies | What breaks without it |
|---|---|---|---|
| CG 20 10 | Ongoing operations | While your crew is actively on the job | GC unprotected during active work |
| CG 20 37 | Completed operations | After your work is finished and accepted | GC unprotected for defects that surface later |
Many disputes appear months after a job closes: a roof leaks, a slab cracks, a panel fails. That is completed operations territory, and only CG 20 37 reaches it. If your exhibit lists only CG 20 10, the GC's lawyers will usually catch the gap at closeout and withhold retainage until you fix it.
The Insurance Services Office (ISO) publishes these standard forms, and you can confirm form language against ISO's own description of CGL endorsements at verisk.com/insurance/products/iso-forms.
Primary and non-contributory and waiver of subrogation: the two riders that travel with it
An additional insured endorsement rarely travels alone. Two companion requirements often ride in the same insurance exhibit:
- Primary and non-contributory: your policy pays first and does not ask the GC's own policy to chip in. Without this, your insurer can argue the GC's policy should share the loss, which defeats the point of being added.
- Waiver of subrogation: your insurer gives up its right to sue the GC to recover what it paid. This stops your own carrier from circling back on the party you were required to protect.
A GC's exhibit that asks for "additional insured, primary and non-contributory, waiver of subrogation" is asking for three distinct endorsements, not one. Read the whole exhibit before you sign. We walk through decoding one line by line in this guide to the insurance requirements exhibit in a subcontract.
What to check before you buy
The real question is never "what policy should I buy." It is "the GC sent the exhibit, can I sign it?" The honest answer depends on three things an insurer either did or did not endorse onto your policy.
Don't buy yet if your exhibit requires CG 20 37 and your quote only includes CG 20 10. You will pay for a policy that fails at closeout. Fix the form list first, then bind.
Where Erni sits
Erni does not sell you the endorsement and does not rate your policy. Erni reads the paperwork the moment it lands and tells you what just changed: which forms the exhibit demands, whether a COI alone will clear the GC's compliance portal, and what to send your agent so the endorsement actually gets issued.
That matters because the trigger is never abstract. It is a certificate deadline, a portal rejection, or a GC withholding payment pending a COI. The same event-to-obligation logic covers related trades questions, like how your experience mod affects your construction bids and what a ghost policy in workers comp really is, because one changed requirement usually drags two others behind it.
One caution on geography: clause mechanics are national, but licensing and workers' comp thresholds are state-administered and vary. Check which rules are federal versus state in this breakdown of federal vs state business rules before you assume a figure applies everywhere.
The closing provocation
Many contractors treat the COI as the deliverable. It is not. The COI is a receipt that says a form exists somewhere. The endorsement is the thing with teeth. If the industry keeps letting a 30-second certificate stand in for a real policy change, the party who gets burned is always the sub who signed believing the paperwork matched. Demand the endorsement form every renewal, or accept that your "additional insured" line is a promise no one is keeping.
Build this with Erni
Tell Erni which trade you run, how many you employ, and paste the insurance exhibit the GC just sent. Erni returns exactly what each line demands, whether your current COI clears it, and the plain-English ask to send your agent, with honest "don't sign yet" flags where the forms don't match. Where the best-fit path has no offer attached, Erni says so.
→ Check my paperwork with Erni
Frequently Asked Questions
Q: Do I need an additional insured endorsement if my COI already says additional insured? A: Yes. A COI only announces coverage, it does not grant it. You need the actual endorsement form (CG 20 10 and usually CG 20 37) on your GL policy, because a GC can only tender a claim against an endorsement, not against a certificate line.
Q: What is the difference between additional insured and named insured? A: The named insured owns the policy and is covered fully; an additional insured is added by endorsement and is only covered for liability arising out of your work. The GC becomes an additional insured, never a named insured on your policy.
Q: What is the difference between CG 20 10 and CG 20 37? A: CG 20 10 covers ongoing operations while your crew is on the job; CG 20 37 covers completed operations after your work is finished and accepted. Many commercial subcontracts require both, and missing CG 20 37 commonly triggers withheld retainage at closeout.
Q: How does additional insured work on a GL policy? A: Your insurer attaches an endorsement that extends your policy's defense and indemnity to the GC for claims arising out of your work. When a covered claim hits, the GC tenders it to your carrier, and your carrier defends them, provided the endorsement is actually on file.
Q: Is primary and non-contributory the same as additional insured? A: No. Additional insured adds the GC to your policy; primary and non-contributory is a separate endorsement that makes your policy pay first without asking the GC's own policy to contribute. Exhibits usually require both plus a waiver of subrogation, which is a third distinct endorsement.
Q: What should I ask my agent for when a GC requires additional insured status? A: Ask for the specific form numbers in the exhibit, usually CG 20 10 and CG 20 37, plus primary and non-contributory and waiver of subrogation if listed. Request the endorsement documents themselves, not just the COI, and reconfirm them at every renewal.
Maintained by the Erni team.