Section 602 establishes the five construction types used throughout the IBC to classify buildings and set appropriate fire safety requirements. Type I construction requires all building elements to be of noncombustible materials meeting specific fire-resistance ratings. Type IA requires 3-hour fire-resistance for primary structural elements, floor-ceiling assemblies, and roof assemblies, with 2-hour for perimeter walls and 1-hour for interior walls and columns. Type IB reduces these requirements to 2-hour for primary elements, 1-hour for floor-ceiling assemblies, and varying ratings for walls. Type II noncombustible construction has no required fire-resistance ratings but mandates noncombustible materials throughout. Type II buildings are often used for commercial and industrial structures where cost is a primary consideration. Type III wood-frame construction with masonry or noncombustible exterior walls requires 1-hour fire-resistance for floor-ceiling assemblies and 2-hour for exterior walls, permitting combustible interior structural elements. Type IV heavy timber construction requires solid or laminated wood structural members with minimum dimension thresholds (8x8 or larger) and 2-hour exterior walls, creating inherently fire-resistant structures due to timber mass. Type V combustible construction permits all elements to be of combustible materials with only limited fire-resistance requirements. Unrated Type V construction has no mandatory fire-resistance ratings, while protected Type V requires 1-hour fire-resistance for certain elements. Floor-ceiling and roof-ceiling assemblies are tested per ASTM E119 to determine fire-resistance ratings.