In Type IV construction, cross-laminated timber must be permitted within exterior wall assemblies with a _____ hour rating or less.

In Type IV construction, cross-laminated timber has specific requirements regarding its use in exterior wall assemblies, particularly concerning fire resistance ratings. The correct answer, which indicates a 2-hour rating, is significant because it aligns with the standards set forth in building codes that address fire safety and structural integrity.

A 2-hour fire rating allows for effective performance of fire-resistive assembly, which inhibits the spread of fire and maintains the structural integrity of the building during a fire incident for a longer duration than lower ratings. This is critical in Type IV construction, where materials such as cross-laminated timber are used extensively and need to meet stringent requirements in order to balance fire safety with the benefits of using innovative timber systems.

Using a lower rating, such as 1 hour, would not provide adequate protection to both the structure and its occupants during a fire incident, as it may succumb to fire exposure more rapidly. Similarly, higher ratings like 3-hour or 4-hour exceed the requirements for Type IV construction as specified in building codes, which aim for a balance between fire safety and the practical use of materials. Thus, the focus on the 2-hour rating reflects the regulatory standards that ensure safety while still allowing the use of contemporary materials like cross