What material is typical in Type IV construction?

In Type IV construction, heavy timber is the distinguishing feature. This type of construction employs large pieces of timber, often called "heavy timber" or "mill construction," which are typically at least 5 inches nominal thickness for structural components. The use of heavy timber provides significant fire resistance due to the greater mass and slower combustion rates of larger wood members as compared to lighter materials.

Additionally, heavy timber structures are designed to take advantage of wood's natural strength and stability, allowing for expansive open spaces without the need for extensive support systems. The configuration promotes both structural integrity and aesthetic appeal, often seen in warehouses and older commercial buildings.

While lightweight steel, wood frame, and reinforced concrete are common in other construction types, they do not define Type IV. Lightweight steel is more characteristic of Type II construction, wood frame is associated with Type V, and reinforced concrete is associated with Type I construction. Understanding these classifications helps in recognizing the unique attributes and fire safety considerations inherent to each construction type.