Exhibit 99.1 Summit Materials, Inc. Reports First Quarter 2024 Results Margin Expansion Fueled by Pricing Momentum and Operational Improvements Raises 2024 Synergy Target to At Least $40 million Adjusting 2024 Guidance Higher DENVER, CO. - (May 1, 2024) - Summit Materials, Inc. (NYSE: SUM) (“Summit,” “Summit Materials,” “Summit Inc.” or the “Company”), market-leading producer of aggregates and cement company, today announced results for the first quarter ended March 30, 2024. All comparisons are versus the ...