What type of building construction is known as heavy timber?

Heavy timber construction is specifically characterized by the use of large wooden members that are typically at least 5 inches by 5 inches in size. This construction type is classified as Type IV according to the National Fire Protection Association (NFPA) and various building codes. The heavy timber components provide a significant degree of fire resistance compared to typical wood framing, due to the thickness of the timber and its ability to char rather than ignite quickly, creating a protective layer.

In Type IV construction, the structural elements, including beams and columns, are made of solid, heavy lumber, which gives it distinctive fire-rated qualities and structural integrity. While Types I, II, and V have other materials and configurations, they do not incorporate the heavy timber aspect that defines Type IV. Therefore, identifying heavy timber construction correctly as Type IV reflects an understanding of the materials and fire resistance properties associated with this class of buildings.