© SCS Global Services Page 2 of 5 Assurance Team and Methodology Our team was comprised of Tina Sentner, Dr. Gerard Mansell, Vincent Katharua , Tavio Benetti and Neil Mendenhall with qualifications available online and upon request. SCS’ Assurance Team undertook the following activities in order to render our opinion : § § Reviewed management systems and governance documents developed as a part of Owens Corning’s sustainability management system , which includes their identification of material topics , stakeholder engagement, mechanisms for stakeholder responsiveness , evaluation of impact and cal culation methods § § Reviewed and analyzed primary performance data collected at the site s and aggregated at the corporate level to identify any material mis statements or calculation errors. § § Conducted interviews with management and key staff in the US, Asia and Europe and requested procedures and data from a sample of Owens Corning’s regions and sites; and § § Review ed the Sustainability Report for material misstatements and its alignment to the requirements of the Global Reporting Initiative (GRI) Standards. Limitations SCS conducted interviews with management and staff, reviewed governance documents and data, and per formed limited recalculations on aggregate and site -specific data through risk -based sampling . These processes enabled SCS to provide a moderate level of assurance on Owens Corning’s 202 1 Sustainability Report, which reduces the risk of our conclusions be ing in error but does not reduce the risk to zero. The assurance did not cover financial data such as the balance sheet, the income statement, and the cash flow statement , technical descriptions of buildings, equipment and production processes or other information not related to sustainability or already supported by existing documents, such as third -party audits or certifications. Opinion and Findings Based on our methodo logy and the activities described above, it is our opinion that: § There is no evidence to suggest that Owens Corning’s management systems, governance documents, data collection methods, and KPI calculations have material errors. Owens Corning’s reporting o f 2021 Scope 3 greenhouse gas emissions, water use, waste, air pollution, VOCs, social performance indicators, and progress towards 2030 sustainability goals were assured at a moderate -level and no material errors or misstatements were identified. § Owens Corning reported Scope 1, 2, and scope 3 categories 1, 3, 4, 6, 7, 9 and 12 GHG emissions, energy us e, employee engagement (% responding and % actively engaged),and types and amounts of philanthropic contributions was assured at a high -level and this data can be considered reliable. § The Report adequately reflects the organization’s alignment to, and implementation of the AA1000AS v3 (2020) principles of Inclusivity, Materiality, Responsiveness, and Impact in its operations. Owens Corning has processes in p lace for consulting and engaging with its key stakeholders in a structured and systematic manner . 2021 Owens Corning Sustainability Report | Appendices | 346 ASSURANCE STATEMENT Appendix F