The Tenth Circuit Court of Appeals affirmed the district court’s finding that Cincinnati Insurance Company must share defense costs for the additional insured with Liberty Mutual Insurance Company. Wolpert v. Cincinnati Ins. Co., 2026 U. S. App. LEXIS 11581 (10th Cir. April 23, 2026)

Simon Contractors was the general contractor for a highway construction project. S&J Signs was a subcontractor. The subcontract required S&J to obtain a policy naming Simon as an additional insured. S&J also agreed to protect the project with “lights, barriers, supports and guards.” Finally, S&J agreed to defend Simon against all liability and lawsuits.

S&J secured a policy with Cincinnati which named Simon as an additional insured. Under the Who Is An Insured provision of the policy, any organization S&J agreed with in writing to add to the policy was an additional insured, but only with respond to ‘bodily injury caused, in whole or in part, by “Your acts or omissions.” Simon also had its own commercial general liability policy with Liberty.

While the project was under construction, two tractor-trailer drivers were involved in a rollover wreck. Both drivers filed lawsuits naming S&J and Simon as defendants. Both drivers alleged (1) the project’s road had steep edge drop-offs and (2) there were no warning signs or barriers. Both drivers alleged that S&J and Simon were at fault due to their negligence.

Liberty – on behalf of its insured, Simon – requested that Cincinnati provide a defense to Simon pursuant to the additional insured policy. Cincinnati declined coverage, deciding that the allegations in the underlying lawsuits did not arise out of or have any connection to S&J’s work.

Liberty filed a declaratory judgment action seeking a determination of rights with respect to the additional insured policy. The district court granted Liberty’s motion for summary judgment and denied Cincinnati’s cross-motion. The district court held that the allegations in the underlying suits triggered Cincinnati’s duty to defend Simon because the injuries had some causal relationship to S&J’s acts and omissions.

Cincinnati appealed arguing that the underlying lawsuits did not establish the tractor-trailer drivers’ injuries were “caused, in whole or in part” by S&J’s acts or omissions.

The Tenth Circuit disagreed. At issue was whether the allegations in the underlying lawsuits triggered Cincinnati’s duty to defend Simon under the additional insured policy. The dictionary definition of “in part” meant partially or somewhat. This meant that the additional insured policy applied if S&J’s acts or omissions were alleged to have even partially caused the injuries. The court found there was a sufficient causal connection alleged between S&J’s work and the tractor-trailer drivers’ injuries to trigger the additional insured policy. Both underlying plaintiffs alleged that they sustained injuries because of Simon and S&J’s acts and omissions.

Cincinnati also argued that the allegations in the underlying lawsuits were unrelated to S&J’s “ongoing operations.” Again turning to the dictionary definition, “ongoing operations” meant S&J’s work while the project was in progress. S&J’s acts or omissions in the performance of its ongoing operations meant anything work-related that S&J did – or failed to do – in connection with the project before its completion.

Because the injuries alleged in the underlying lawsuits (1) were in part due to S&J’s acts or omissions and (2) occurred prior to the completion of the contracted-for work, Cincinnati had a duty to defend Simon.