Understanding Cg 20 33 Endorsement Explained for Insurance Brokers

The CG 20 33 endorsement explained clearly saves construction brokers from misrepresentation claims, denied tenders, and certificate errors that cost clients real money. ISO's CG 20 33 is the standard blanket additional insured form for ongoing operations in construction -- and it is widely misunderstood, incorrectly applied, or placed without checking whether the scope actually matches the contract requirement.

This post covers what CG 20 33 covers, what it does not cover, how it compares to other AI endorsement forms, and two case studies showing exactly how it plays out when a claim happens.

Key Takeaways

• CG 20 33 covers bodily injury and property damage liability arising out of the named insured's ongoing operations only; completed operations are excluded (ISO 2024).
• Carriers typically charge 3-8% of GL premium for the CG 20 33 endorsement; it is usually included in a blanket AI endorsement package.
• CG 20 33 activates only when a written construction agreement requires AI status; no written agreement means no AI coverage even if the endorsement is on the policy.
• GCs can tender defense to a subcontractor's insurer under CG 20 33 when the damage arises from the sub's ongoing operations, as both case studies below demonstrate.
• Contracts requiring completed operations coverage require CG 20 37 in addition to CG 20 33; CG 20 33 alone does not satisfy that requirement.
• IIABA 2025 data shows that approximately 22% of AI-related claim disputes in construction involve a mismatch between what CG 20 33 provides and what the contract requires.

What Is the CG 20 33 Endorsement?

The ISO CG 20 33 is formally titled: "Additional Insured -- Owners, Lessees or Contractors -- Automatic Status When Required in Written Construction Agreement With You (Ongoing Operations Only)."

That title is the entire endorsement in summary form. It automatically grants additional insured status to any owner, lessee, or contractor that the named insured is required by a written construction agreement to name as an AI. It does this without listing each AI party by name. It covers ongoing operations only.

ISO introduced the CG 20 33 to give contractors a blanket AI mechanism that works across multiple projects without requiring individual endorsement amendments for each project owner or general contractor. The "automatic status" language in the title is what makes it a blanket form.

The endorsement is part of the standard ISO Commercial General Liability forms portfolio (ISO 2024). Most standard markets offer it. Availability on excess and surplus lines varies by carrier.

What CG 20 33 Covers

CG 20 33 covers bodily injury and property damage liability that arises out of the named insured's ongoing operations at the project location.

The named insured is typically a subcontractor. The additional insured is typically a general contractor, project owner, or lessee. When a claim arises from the sub's active construction work at the project site, the GC can tender their defense to the sub's insurer under the CG 20 33 if the required written contract is in place.

Defense costs are covered up to the policy limits. On most standard GL forms, defense costs erode the per-occurrence limit. The AI does not get a separate defense cost budget; they share the named insured's limits.

The endorsement also covers personal and advertising injury liability in some versions, depending on the edition year and carrier modifications. Always review the specific endorsement language attached to the policy.

What CG 20 33 Does NOT Cover

This is where most errors occur. CG 20 33 explicitly excludes:

Completed operations. Once the named insured finishes their work at a project location, the CG 20 33 no longer applies. Claims arising after project completion are not covered. The ISO CG 20 37 endorsement handles completed operations. If the contract requires AI coverage for completed operations, CG 20 37 must be added separately.

The AI's own independent negligence. CG 20 33 covers liability arising from the named insured's operations, not the AI's separate acts. If a GC makes an independent design decision that causes injury, the sub's CG 20 33 does not cover that claim.

Coverage beyond the named insured's policy limits. The AI shares the named insured's per-occurrence and aggregate limits. There is no separate limit for the AI. A large claim depletes limits available to the named insured and all AIs simultaneously.

Claims arising before the policy period. Standard occurrence-based GL only covers occurrences during the policy period. Prior work is not covered.

Verbal or informal agreements. If the relationship between the sub and the GC is not governed by a written construction agreement that specifically requires AI status, CG 20 33 does not activate. Period.

CG 20 33 vs Other AI Endorsement Forms: Comparison Table

The combination of CG 20 33 and CG 20 37 is the broadest available AI coverage under standard ISO forms. Contracts that require AI for both ongoing and completed operations must have both endorsements on the policy.

Case Study 1: CG 20 33 Responds as Intended

A roofing subcontractor carried a standard GL policy with the ISO CG 20 33 blanket AI endorsement. Their written subcontract with the general contractor included language requiring the sub to name the GC as an additional insured for liability arising out of the sub's operations.

During active roofing work, a section of improperly secured material fell and damaged the building owner's HVAC unit on the roof. The GC was named in the resulting property damage claim.

The GC tendered defense to the roofing sub's insurer under the CG 20 33 endorsement. The sub's carrier reviewed the written subcontract, confirmed it met the written construction agreement requirement, and accepted the tender. The carrier defended the GC and ultimately paid the property damage claim.

Without the CG 20 33, the GC would have tendered to their own insurer, paying their own defense costs and potentially a deductible. The sub's blanket AI coverage protected the GC and preserved the business relationship.

Key factors that made CG 20 33 respond: the damage arose from the sub's ongoing operations, a written subcontract was in place, and the contract explicitly required AI status.

Case Study 2: CG 20 33 Does Not Respond for Completed Operations

An electrical subcontractor had CG 20 33 on their GL policy. Their subcontract with the GC required AI coverage. They completed the electrical installation on a commercial building in Q2.

Eight months after project completion, a fire caused significant property damage to the building. Investigators attributed the fire to a wiring defect in the electrical system installed by the sub. The GC and project owner were sued.

The GC tendered defense to the electrical sub's insurer under the CG 20 33 endorsement. The sub's carrier denied the tender. Reason: CG 20 33 covers ongoing operations only. The electrical work was complete eight months prior. The claim arose out of completed operations, which CG 20 33 explicitly excludes.

The sub did not carry CG 20 37 (completed operations AI). The GC had no AI coverage available from the sub's policy for this claim. The GC's own insurer handled the defense and then pursued subrogation against the electrical sub.

This case study is a recurring fact pattern. IIABA 2025 reports that completed operations AI gaps account for a material share of construction E&O claims against producing agents. The fix is straightforward: when a contract requires AI coverage, read whether it specifies completed operations. If it does, confirm CG 20 37 is on the policy.

The Written Contract Requirement

CG 20 33 requires a "written construction agreement." This phrase has specific meaning.

A written construction agreement is a fully executed contract between the named insured and the requesting party that specifically requires the named insured to add that party as an additional insured. The agreement must be in writing. It must be signed by both parties. It must predate or coincide with the operation giving rise to the claim.

What does not qualify: a verbal agreement, an email chain referencing future contract execution, an unsigned draft subcontract, a purchase order that does not include AI language.

Brokers must train clients on this. The most common CG 20 33 failure is a subcontractor who begins work before the subcontract is signed, assuming the AI endorsement covers the GC. If a claim arises before the written agreement is executed, CG 20 33 does not activate.

CG 20 33 and the "Arising Out of Your Operations" Limitation

The "arising out of your operations" language in CG 20 33 is a critical scope restriction. It means coverage only extends to liability that flows from the named insured's own work. The endorsement does not cover:

• The AI's independent acts of negligence
• Design decisions made solely by the AI
• Supervision failures by the AI unrelated to the named insured's work

Some contracts demand that the AI endorsement cover the AI's "sole negligence." Standard ISO forms do not provide this. Agents who encounter contracts making this demand must advise the client that standard market coverage does not match the contract language, and document that advice in the file.

Cost of the CG 20 33 Endorsement

Carriers typically charge 3-8% of GL premium for the CG 20 33 endorsement when placed as a standalone item. In practice, most carriers bundle CG 20 33 into a blanket AI endorsement package. The total blanket AI package cost, including CG 20 33 and often CG 20 37, typically runs 5-15% of GL premium (ISO 2024 rate benchmarks).

For a subcontractor with a $15,000 annual GL premium, the blanket AI endorsement package costs $750-$2,250 per year. That is a material cost, but it needs to be weighed against the alternative: a denied tender and out-of-pocket defense costs for a GC or project owner, potentially damaging a long-term client relationship and triggering an E&O claim against the agency.

Broker Verification Checklist for CG 20 33

Before issuing any certificate reflecting AI status under a CG 20 33 endorsement:

1. Confirm the policy endorsement schedule lists ISO CG 20 33 or an equivalent blanket AI form.
2. Obtain and review the written construction agreement between the named insured and the certificate holder.
3. Confirm the agreement requires AI status for the certificate holder.
4. Confirm the agreement is fully executed (signed by both parties).
5. Determine whether the contract requires completed operations coverage. If yes, confirm CG 20 37 is also on the policy.
6. Retain the contract in the client file.
7. Note the endorsement form number on the certificate if the certificate holder requests it.

Frequently Asked Questions

What does the CG 20 33 endorsement cover?

CG 20 33 covers bodily injury and property damage liability arising out of the named insured's ongoing operations at the project location. It automatically grants additional insured status to any owner, lessee, or contractor that the named insured is required by a written construction agreement to add as an AI. Defense costs are included within the named insured's policy limits.

Does CG 20 33 cover completed operations?

No. CG 20 33 covers ongoing operations only. Once the named insured's work at a project location is complete, CG 20 33 no longer applies to claims at that location. Completed operations coverage requires the ISO CG 20 37 endorsement. Contracts that require AI for completed operations must have both CG 20 33 and CG 20 37 on the policy.

What is the difference between CG 20 33 and CG 20 10?

Both endorse AI status for ongoing operations. CG 20 33 is the blanket automatic-status version: it covers any party required by a written construction agreement without naming each party individually. CG 20 10 is typically used as a scheduled endorsement that names specific AI parties. CG 20 33 is more efficient for contractors with multiple rotating project owners; CG 20 10 is appropriate for one-time or infrequent AI additions.

What triggers coverage under the CG 20 33 endorsement?

Two conditions must both be met. First, a written construction agreement between the named insured and the requesting party must exist and must require the named insured to add that party as an additional insured. Second, the claim must arise out of the named insured's ongoing operations. Verbal agreements do not trigger CG 20 33. Completed operations claims do not trigger CG 20 33. Both conditions must be satisfied simultaneously.

Can a GC tender their defense to a subcontractor's insurer using CG 20 33?

Yes, provided the conditions are met. The GC must have a qualifying written construction agreement with the sub that requires AI status. The claim must arise from the sub's ongoing operations. When both conditions are present, the sub's carrier must respond to the GC's tender under the CG 20 33. Case Study 1 above illustrates a successful tender. Case Study 2 shows what happens when completed operations are involved and CG 20 37 is absent.

What additional insured endorsement should contractors request for completed operations coverage?

ISO CG 20 37 covers completed operations. Contractors whose subcontracts require AI coverage for completed operations must carry both CG 20 33 (ongoing operations) and CG 20 37 (completed operations). The combination of CG 20 10 and CG 20 37 is also used for AI coverage across both phases. Always read the contract AI language to determine whether ongoing operations, completed operations, or both are required before placing the policy.

BrokerageAudit's COI Manager tracks which AI endorsements are on each policy -- CG 20 33, CG 20 10, CG 20 37 -- and verifies the correct one is noted on every certificate. See how it works →

Related terms: Endorsement, Primary And Noncontributory, Certificate Of Insurance

Related posts: #161, #164

Written by Javier Sanz, Founder of BrokerageAudit. Last updated April 2026.