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Understanding the Subtypes of Category IV Construction

Understanding the Subtypes of Category IV Construction

Heavy and mass timber construction is on the rise. How does fire safety factor into the public’s desire for sustainable, natural construction elements, and what should architects be aware of when designing with beautiful, durable, and efficient timber material?

Up to Code

Due to the expanding market for mass timber structures, in 2021 the International Building Code (IBC) added subtypes to their Type IV classification, which encompasses timber construction. The type is now divided into three categories of fire resistance, with varying fire suppression systems required for each:

  • Type IV-A is for buildings with all structural elements, internal and external, completely protected with noncombustible protection, such as Type X gypsum board. This is the highest fire resistance level in this type.
  • Type IV-B is for buildings with some interior structural elements exposed, but with all concealed spaces and shafts fully protected with noncombustible protection.
  • Type IV-C is for buildings with most structural elements left unprotected, relying instead on the inherent fire-resistant nature of the mass timber itself.

Safety First

The safety of occupants is ultimately the most important aspect of any structure. With the ICC’s updated requirements, they have laid the foundation for mass timber construction to follow strict fire safety rules while also satisfying the public’s demand for safe structures. The Type IV subtypes also affirm that modern mass timber is here to stay, and that it’s a safe, viable alternative to traditional concrete and steel.

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