What defines Type IV Heavy Timber construction?

Type IV Heavy Timber construction is defined primarily by the use of solid or laminated wood for interior structural members, and a critical aspect of this construction type is that it does not have concealed spaces. This is important because the absence of concealed spaces reduces the likelihood of fire spreading undetected through walls and other hidden areas, which can significantly enhance the safety of the structure during a fire situation.

In this type of construction, the dimensions of the wooden members typically exceed 4 inches by 4 inches, which contributes to their structural stability and fire resistance. However, the defining feature that sets Type IV apart is the construction method and the openness of the wood systems, allowing for better visibility and access for firefighting operations.

While it is true that external walls must often be made of fire-retardant materials in various construction types, the focus of Type IV Heavy Timber is more on the characteristics of the interior wood members and their configuration rather than on the combustibility of exterior walls. Therefore, option C most accurately captures the essence of Type IV Heavy Timber construction.