Which type of construction is typically the least fire-resistant?

The correct answer refers to Type III construction, specifically III-A, which is generally considered to be the least fire-resistant compared to the other types of construction mentioned. Type III construction, often referred to as "ordinary" construction, typically consists of exterior walls that are built of noncombustible materials but can have interior elements that are combustible, such as wood framing. This combination results in lower overall fire resistance.

Building codes categorize construction types based on their fire-resistance ratings, which influence the safety measures applied to a structure. Type I-A construction is made with noncombustible materials throughout and has high fire-resistance ratings, while Types II-A and IV also afford greater fire resistance through specific material requirements and structural configurations. Thus, Type III-A, with its balance of noncombustible exteriors and potentially combustible interiors, presents the least resistance to fire among the choices.

Fire-resistance ratings are essential to consider in building design and safety, affecting everything from material choices to compliance with safety codes and regulations. Understanding these classifications helps architects engage better in the design process and factor in safety considerations efficiently.