Building doors and windows belong to the Building Materials division within the construction industry. This division encompasses a wide range of materials used in the construction process, including doors, windows, and other components that contribute to the structural integrity and functionality of buildings. The reason for this categorization lies in the essential role these elements play in the construction process and the industry's broader classification.

According to the U.S. Census Bureau, the construction industry is segmented into several divisions, with Building Materials being one of the primary categories. This division includes the manufacturing and distribution of materials such as steel, concrete, glass, and other components used in building construction. Doors and windows, being integral to the building envelope, are included in this category due to their functional and structural contributions.

Data from the U.S. Bureau of Labor Statistics (BLS) indicates that the building materials manufacturing industry employed approximately 1.1 million workers in 2020. This figure underscores the significance of the Building Materials division within the construction industry. Doors and windows, as part of this division, are essential components that not only provide security and privacy but also contribute to energy efficiency and aesthetic appeal.

Moreover, the American Architectural Manufacturers Association (AAMA) reports that the window and door industry generates billions of dollars in revenue annually. This economic impact further highlights the importance of doors and windows within the Building Materials division. The industry's focus on innovation and sustainability in door and window manufacturing aligns with the broader goals of the construction industry, making them a natural fit within the Building Materials division.

In conclusion, building doors and windows belong to the Building Materials division due to their fundamental role in the construction process, their contribution to the structural integrity and functionality of buildings, and the significant economic impact of the industry. The classification reflects the industry's emphasis on materials that are essential to the construction process and the broader goals of the construction sector.