A certificate of insurance (COI) is a one-page summary that proves you had a policy on the day it was issued, and that's all it proves; it does not create coverage, change coverage, or guarantee anyone is actually protected. The dangerous gap is "additional insured" status: a COI can list a GC as an additional insured, but that means nothing unless the matching endorsement is actually on your policy. Here is what a COI does and does not do, and what to check.
What a COI is (and isn't)
A COI is a standard ACORD form that summarizes your policy types, limits, carrier, effective and expiration dates, and named insureds. It is proof of coverage as of the issue date, and insurers issue it free on request.
What it is not: it is not the policy, and it does not create or modify coverage. A certificate is a snapshot, not a contract. Coverage lives in the policy and its endorsements, not on the certificate.
In US construction this exchange is culturally mandatory. A GC will require a valid COI from every sub before work starts, and some owners, cities, and HOAs require a project-specific COI naming them. GCs are motivated to collect them, because at their own insurance audit, payments to subs without valid COIs get reclassified as the GC's own payroll at the sub's trade rate, which is often the highest rate on the board.
Additional insured: the endorsement is what counts
When a GC or owner is named as an additional insured (AI) on your general liability, your insurer must defend and indemnify them for claims arising from your work. That protects their limits and puts your carrier first in line. GCs demand it, and failing to provide it can mean contract default and withheld payment.
Here is the trap: a line on the COI that says "GC is additional insured" only has effect if the AI endorsement actually exists on your policy. Watch for "ATIMA" (as their interests may appear) language, which does not by itself add anyone. There has to be a real endorsement behind it. Ask your broker to confirm the AI endorsement is on the policy, not just typed onto the certificate. A certificate that promises AI status you do not actually carry protects nobody and can blow up into a coverage fight after a loss.
CG 20 10 vs CG 20 37: ongoing vs completed operations
The two common AI endorsement forms cover different time windows, and the difference matters:
- CG 20 10 covers ongoing operations, meaning while you are still working on the job.
- CG 20 37 covers completed operations, meaning after you are done and gone.
Since construction defects usually surface after completion, CG 20 10 alone gives the GC nothing once the job is finished. Many contracts require both so the GC is protected during and after the work. Check the exact form and edition your contract specifies, because ISO tightened the language in its 2004 and 2013 revisions to limit AI coverage to your negligence rather than the broader older versions.
Blanket additional insured and why subs use it
A blanket AI endorsement automatically extends additional insured status to any party you are contractually required to name, instead of scheduling each GC one at a time. If you work for several GCs at once, blanket AI saves you re-issuing a separate endorsement for every job. It is the practical option for a busy sub. Just confirm the blanket wording actually reaches completed operations, not only ongoing operations, if your contracts require both.
Waiver of subrogation
Subrogation is your insurer's right to sue a negligent third party after it pays a claim. A waiver of subrogation (WOS) endorsement gives up that right against the GC or owner, so after a loss the carriers settle it rather than everyone suing each other. GCs commonly require it.
The trap is timing: a WOS must be on the policy before the loss happens. Adding it after the fact is worthless. If your contract requires a WOS, verify the endorsement is in place before you mobilize to site, not after something goes wrong.
Common questions
Does a certificate of insurance mean I'm actually covered?
It only proves a policy existed on the day the certificate was issued; it does not create coverage or guarantee anyone is protected. A COI is a one-page ACORD summary, not the policy, and it cannot add coverage that is not in the underlying policy. In particular, a certificate that lists someone as an additional insured means nothing unless the matching endorsement is actually on the policy. Always confirm the real policy and endorsements, not just the certificate.
What does "additional insured" actually do?
Naming a GC or owner as additional insured on your general liability makes your insurer defend and indemnify them for claims arising from your work, protecting their limits and putting your carrier first. But it only works if the additional insured endorsement is actually on your policy; a line on the certificate is not enough, and "ATIMA" language does not add anyone by itself. Ask your broker to confirm the endorsement exists, and check whether it covers completed operations, not just ongoing work.
What's the difference between CG 20 10 and CG 20 37?
CG 20 10 covers the additional insured during your ongoing operations; CG 20 37 covers them for completed operations after you finish. Construction defects usually appear after the job is done, so CG 20 10 alone leaves the GC unprotected once you leave the site. That is why many contracts require both forms. Check the exact form and edition your contract names, because ISO revisions in 2004 and 2013 narrowed the language to your own negligence.
What is a waiver of subrogation and why does the GC want one?
A waiver of subrogation gives up your insurer's right to sue the GC or owner after paying a claim, so the carriers settle a loss instead of the parties suing each other. GCs require it to keep an incident from turning into cross-lawsuits between the companies on a job. The catch is timing: a waiver must be on the policy before the loss happens, because adding it afterward is ineffective. If your contract requires one, confirm the endorsement is in place before you start work.
Can I add additional insured or waiver of subrogation after an accident?
No. Both an additional insured endorsement and a waiver of subrogation have to be on the policy before the loss occurs; adding either retroactively does not work. That is why you verify these endorsements are actually on your policy before you mobilize to a job, not after something goes wrong. A certificate promising coverage you never actually put in place leaves you exposed to contract default and a coverage dispute exactly when you can least afford one.
The honest bit
- The form numbers (CG 20 10, CG 20 37) and the ACORD certificate are national industry standards, but editions change and every carrier's endorsement wording differs, so read the actual endorsement, not the certificate.
- What your contract requires (which forms, both ongoing and completed operations, and a WOS) governs, so match the endorsements to the contract before you sign, and confirm they are on the policy before you start.
- This is general guidance, not insurance or legal advice. Route state, municipal, and HOA certificate requirements to Working in Your State.
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