Koppers Holdings Inc.

Our management, with the participation of the Chief Executive Officer and Chief Financial Officer and utilizing the Committee of Sponsoring Organizations of the Treadway Commission (COSO) Internal Control – Integrated Framework (2013), have evaluated the effectiveness of our disclosure controls and procedures, as defined in Rules 13a-15(e) and 15d-15(e) of the Securities Exchange Act of 1934 as of the end of the period covered by this report. Based on that evaluation, the Chief Executive Officer and Chief Financial Officer have concluded that these controls and procedures were effective as of the end of the period covered by this report.

In the first quarter of 2026, we completed another phase of our new enterprise resource planning (ERP) system implementation and migrated part of our RUPS business onto the new system. As a result, we have implemented updates and changes to our current processes and related control activities. As the phased implementation continues over the next several years, we will continue to experience certain changes to our processes and procedures which will result in changes to our internal controls over financial reporting. There are inherent risks in implementing an ERP system and, accordingly, management will continue to evaluate the design and operating effectiveness of these controls.

Except as noted above, there was no change in our internal control over financial reporting (as such term is defined in Rule 13a-15(f) under the Exchange Act) that occurred during the quarter ended March 31, 2026 that have materially affected, or are reasonably likely to materially affect, our internal control over financial reporting.

PART II—OTHER INFORMATION

The information set forth in Note 12 to the Condensed Consolidated Financial Statements of Koppers Holdings Inc. included in Item 1 of Part I of this report is incorporated herein by reference.