Additional Insured Endorsements: CG 20 10 vs CG 20 33 vs CG 20 37 — What the Form Numbers Actually Mean
Additional insured (AI) endorsements are how a subcontractor's commercial general liability (CGL) policy extends coverage to upstream parties — typically the general contractor and project owner. When a GC requires a sub to "name us as additional insured," what they're really asking for is the specific endorsement form that modifies the sub's CGL policy to include the GC's interests.
The specific form matters. Different ISO (Insurance Services Office) standard endorsement forms provide different coverage — some cover only the sub's ongoing operations, some cover completed operations after the work is done, some provide blanket coverage for anyone the sub contracts with. A subcontract requiring the wrong form leaves a coverage gap that surfaces after the project closes when a claim arises from the sub's work.
Construction subcontracts commonly reference specific ISO endorsement forms by number. The three most common:
Common AI endorsement forms
- CG 20 10 — Additional Insured, Owners, Lessees or Contractors — Scheduled Person Or Organization (ongoing operations coverage)
- CG 20 37 — Additional Insured, Owners, Lessees or Contractors — Completed Operations (coverage extends after work is finished)
- CG 20 33 — Additional Insured, Owners, Lessees or Contractors — Automatic Status (blanket AI coverage when required by written contract)
Each form has specific language, specific limitations, and specific edition dates (e.g., 04 13 means April 2013 edition). The edition date matters because ISO revises the forms periodically and different editions have different coverage nuances.
CG 20 10 is the traditional AI endorsement for construction. It adds the named GC (or owner) as an additional insured for liability arising out of the sub's ongoing operations. When the sub is working on the project, the GC is covered. When the sub's work creates a claim during construction, the sub's policy responds on behalf of the GC.
The key limitation: CG 20 10 alone covers only the ongoing operations period — while the sub is actively performing. Once the sub's work is complete, claims arising from the completed work (a roof that fails two years after installation, a floor that cracks after occupancy) don't trigger coverage under CG 20 10 alone. For that, you need CG 20 37 — the completed operations endorsement — on top of CG 20 10.
Requiring CG 20 10 without CG 20 37 is a common drafting error. It provides AI coverage during construction but leaves the GC exposed after the sub's work is complete — exactly when most latent-defect claims arise.
CG 20 37 is the completed operations version. It extends AI coverage beyond the ongoing operations period, covering claims that arise after the sub has completed their work. If the roof the sub installed fails and the building owner sues the GC, the sub's CGL (with CG 20 37 endorsement) responds on behalf of the GC.
The standard construction AI requirement is both CG 20 10 AND CG 20 37 — together they cover the full liability spectrum from start of work through the statute of limitations on construction defect claims (often 10+ years under applicable state statutes of repose).
CG 20 33 is a blanket AI endorsement. Rather than naming specific parties as AIs (which requires the sub's insurer to update the policy schedule each time a new GC is added), it automatically extends AI status to anyone the sub is required by written contract to add as an AI. It covers only ongoing operations — the completed-operations counterpart is CG 20 38 (less common).
Blanket AI endorsements are convenient for subs working with many GCs — they don't have to update the policy for each new subcontract. They're acceptable to GCs that are confident the sub's policy actually includes the endorsement. The tradeoff is slightly less precision about who the AIs are, and some sophisticated risk managers prefer scheduled AI (via CG 20 10 with specifically named parties) for the clarity.
ISO revised the CG 20 10 form in 2004 and again in 2013. The revisions narrowed the coverage in ways that affected construction claims. Key changes:
Significant edition changes
- Pre-2004 editions — broader "arising out of" language that covered AIs for claims involving the sub's work even when the AI was partly at fault
- 2004 edition — added "caused in whole or in part by" language that narrowed coverage to claims where the sub had some causal role
- 2013 edition — further clarified limits and added anti-bunching language regarding multiple insured parties
- Current editions — continue to refine the scope of AI coverage in ways generally narrower than older forms
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For GCs, the practical implication is that subcontract language should specify the edition of the form required, or at minimum require "current ISO CG 20 10 and CG 20 37 forms." Relying on whatever edition happens to be on the sub's policy leaves the coverage scope to chance.
When a sub's COI arrives, the description of operations section should specify the AI endorsement form numbers and editions. A well-drafted COI entry reads something like: "[GC Name] is included as Additional Insured per CG 20 10 04 13 and CG 20 37 04 13 as respects ongoing and completed operations for the [Project Name] project."
A COI that just says "Additional Insured: [GC Name]" without specifying the form is inadequate. The compliance team should bounce it back and request specifics. Until the correct form is identified, the actual scope of AI coverage is unknown.
Most GC subcontracts require not just AI status but also "primary and non-contributory" coverage. This means the sub's AI coverage applies first and doesn't require the GC's own policy to contribute. Without the primary-and-non-contributory language, the sub's insurer and the GC's insurer can argue about who pays first, extending claim resolution and potentially leaving the GC with more exposure.
Primary and non-contributory status usually requires a separate endorsement — often CG 20 01 (Primary and Non-Contributory Other Insurance Condition) or policy-specific wording. The subcontract should require both the AI endorsement and the primary-and-non-contributory endorsement.
The third common endorsement construction subcontracts require is waiver of subrogation. This prevents the sub's insurer from recovering from the GC after paying a claim on the GC's behalf. Without waiver of subrogation, the sub's insurer pays the claim but then may pursue the GC for contribution or indemnity, putting the GC back in the line of fire.
Standard waiver of subrogation endorsements include CG 24 04 (for CGL) and WC 00 03 13 (for workers' comp). The subcontract should require both, specifying the form numbers.
A thorough AI requirement in a construction subcontract
- AI status on CGL via CG 20 10 (ongoing operations) plus CG 20 37 (completed operations), both current ISO editions
- Primary and non-contributory status via CG 20 01 or equivalent
- Waiver of subrogation on CGL via CG 24 04
- Waiver of subrogation on workers' comp via WC 00 03 13
- AI status on auto liability where applicable (CA 20 48 or equivalent)
- AI status on umbrella/excess policies following form from the primary policies
- COI evidence of all the above, with specific form numbers and editions identified
- Sub's agreement to maintain the coverage for the entire statutory period, not just the construction period
Additional insured endorsements are the technical mechanism that extends a sub's CGL coverage to the GC and owner. The specific form matters: CG 20 10 covers ongoing operations, CG 20 37 covers completed operations, CG 20 33 provides blanket coverage, and each has edition-specific language. Requiring a comprehensive AI package — both ongoing and completed operations, primary-and-non-contributory, and waiver of subrogation — protects the GC for the full liability period of the construction defect claims that can surface years after project close. Requiring the wrong forms, or requiring them vaguely, leaves coverage gaps that become apparent only when a claim arrives.
Written by
Jordan Patel
Compliance & Legal
Former corporate counsel specializing in construction contracts and tax compliance. Writes about the documentation layer — COIs, W-8/W-9, certified payroll, notice-to-owner deadlines — and the legal backbone behind audit-ready AP.
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