Towers, spires, domes, and cupolas greater than what height must be constructed of and supported on Type I or II construction?

The correct height threshold is significant for ensuring that structures such as towers, spires, domes, and cupolas maintain safety standards in construction. In building codes, particularly those related to commercial construction, specific materials and methods of building must be adhered to based on the height of a structure.

When structures exceed 85 feet, the increased risk of structural failure or fire necessitates the use of more fire-resistant construction methods, which Type I and II construction provide. Type I construction is made of non-combustible materials, while Type II contains materials that have limited combustibility, both of which enhance the overall fire resistance and structural integrity needed for taller structures.

By establishing 85 feet as the critical threshold, building codes ensure that as the height of the structure increases, the safety and durability of the materials used correspondingly secure the integrity of the building. This requirement is in place to protect not only the occupants of the building but also the surrounding properties and infrastructure.