Which construction type is described by using heavy timber as the structural system?

• A. Type I (Fire-Resistive)
• B. Type II (Noncombustible)
• C. Type IV (Heavy Timber)
• D. Type III (Ordinary)

Answer: (C)

Heavy timber as the structural frame is the defining feature here. In this construction type, the building’s structure is formed from large wooden members—thick posts and beams—that carry the loads, and those timbers are often exposed for their aesthetic and structural clarity. This approach is codified as Type IV, Heavy Timber, and it stands apart from the other types by centering the frame on substantial timber rather than steel or concrete.

Understanding the others helps see why this is the right choice: Type I is designed around high fire resistance with noncombustible construction and protections like fire-rated assemblies; Type II relies on noncombustible materials for both structure and enclosure; Type III uses noncombustible exterior walls with interior elements that may include wood but not as the primary large-frame structural system. Type IV, by contrast, uses heavy timber as the main structural system, with exterior walls often masonry or concrete and interior timber framing, which is why it’s specifically labeled as Heavy Timber. The inherent fire performance of large timber members—char layer formation that slows failure—also aligns with the type’s intent.