Additional insured and waiver of subrogation for subcontractors: a California GC's guide

Short answer

Additional insured (AI) status puts your company on the sub's liability policy, added by endorsement at the sub's request.
There are two parts: ongoing operations (while the sub is working) and completed operations (after the job is done). The ISO forms commonly used are CG 20 10 and CG 20 37.
A certificate of insurance doesn't change the policy. California law requires certificates to say so. The endorsement is what counts.
Ask the sub's insurance agent for copies of the endorsement pages, not just a certificate with boxes checked.

What additional insured means

An additional insured is a person or company that isn't automatically covered by a policy, but is added to it at the request of the policyholder (IRMI definition). For a GC, that usually means being added to your sub's general liability policy, so a claim that comes from the sub's work can be handled under the sub's policy too, not only yours.

Your subcontract decides what you're entitled to. The sub's policy decides what you actually get. You want those two to match.

Ongoing vs. completed operations

Ongoing operations covers you for liability from the sub's work while they're doing it. The ISO form commonly used is CG 20 10.
Completed operations covers you for claims that come from the sub's work after it's finished. The ISO form commonly used is CG 20 37.

Edition dates matter. Since the 1985 edition, CG 20 10 doesn't give the additional insured completed operations coverage, and CG 20 37 was created to fill that gap, so you typically need both (Insurance Journal, 2015). Some policies use the insurer's own forms or "blanket" endorsements instead. Read the actual form.

Why the certificate checkbox isn't enough

A checked "ADDL INSD" box on a certificate doesn't make you an additional insured. Under California Insurance Code §384, a certificate of insurance has to state that it isn't an insurance policy and doesn't amend, extend or alter the coverage of the policies listed, and that the coverage stays subject to all of the policies' terms, exclusions and conditions. If the endorsement doesn't cover you, the certificate won't fix it.

Many additional insured endorsements only apply when there's a written contract with the sub that requires it. An insurance attorney describes an owner who collected papers from 15 subs saying the owner was an additional insured, and wasn't covered because there was no written contract with those subs (Insurance Journal). Sign the subcontract before the sub starts.

Waiver of subrogation

When an insurer pays a claim, it can usually try to recover that money from whoever caused the loss. That's subrogation. A waiver of subrogation is the insurer's acknowledgment that it gives up that right against a party, typically because the policyholder agreed in a contract to waive its own right of recovery (IRMI definition). Waiving recovery before a loss generally doesn't void coverage, but waiving it after a loss can.

Many subcontracts ask for a waiver in your favor on the sub's general liability and workers' comp policies. Like additional insured status, it comes by endorsement, so ask to see it.

What to ask the sub's agent for

The additional insured endorsementsOngoing and completed operations, with the form numbers and edition dates.
Scheduled or blanket?If scheduled, your company's exact legal name should be on it. If blanket, check what it requires (often a written contract signed before the work).
Waiver of subrogation endorsementsOn general liability and workers' comp, if your contract requires them.
Primary and non-contributory wordingIf your contract calls for it, by endorsement.
Policy datesThe policy should be in force for the whole job.

Use the agent listed as "Producer" on the certificate. Then run through the rest of the certificate of insurance checklist and check the sub's license on Sub Check. For trade-by-trade license classes, see the trade pages, for example roofing.

General information for California contractors, current as of November 3, 2026. It isn't legal advice; rules change, so check the official source linked above.