For this reason, The California Ignition Resistant Standard says “that is allowed by code.” Section 602.4 Minimum Solid Sawn Wood Member Size Width in Inches Depth in Inches 8 8 6 10 6 8 6 6 4 6 Types for Ignition Resistant Construction Understanding Building Construction Types To identify buildings most likely to fail under a rapid-fire condition, firefighters and particularly ladder-crews, classify buildings into five categories of Types I – Type V. Type I is a fire-resistive building built from non-combustible materials such as steel structure and concrete. Type III can be new or old construction, a brick-and-joist structure, typically a concrete block structure with the framework, floor trusses, and roof built with wood and other combustible material.