What type of building material is used for the exterior walls in Type IV construction?

In Type IV construction, also known as "Heavy Timber" construction, the exterior walls are made from noncombustible materials. This classification is particularly important because it provides a level of safety in terms of fire resistance. While wood is used extensively in the building's structure, the critical aspect is that the exterior walls must consist of materials that will not easily catch fire or contribute to structural failure in a fire event.

The use of noncombustible materials helps to create a barrier that can protect the interior from external fire sources and helps contain internal fires, preventing them from spreading to the outside. This is crucial for the safety of occupants and the integrity of the building itself as well as for compliance with building codes that prioritize fire safety.

Other options do not appropriately describe the requirements for the exterior walls in Type IV construction, which specifically mandates noncombustible materials to ensure adequate fire protection.