Which construction type is considered heavy timber?

Heavy timber construction, classified as Type IV, is characterized by the use of large wooden beams, posts, and structural elements. This method is often favored for its durability and fire-resistance properties, as the substantial mass of the timber can withstand fire for a longer duration compared to lighter materials.

In Type IV construction, the wood components typically have a minimum nominal dimension of 8 inches, which helps in delaying structural failure during a fire due to the 'charing' effect. When exposed to flame, the surface of the heavy timber will begin to char and insulate the inner wood, thereby prolonging the material's integrity and load-bearing capacity over time, making it advantageous from a fire safety perspective.

In contrast, other construction types such as Type II, Type III, and Type V use lighter materials or have different structural compositions, which do not provide the same level of fire resistance or structural robustness associated with heavy timber. Type II is primarily non-combustible materials but may include some combustible elements; Type III involves a mixture of wood and non-combustible materials but does not follow the same large-dimension timber standard as Type IV; and Type V is focused on light-frame construction, typically using materials like wood which can lead to