This Construction Brief will give you an overview of ISO's Construction Class 4 – masonry noncombustible construction. When you've completed this course, you'll know what an ISO report means when it says a building is masonry noncombustible construction. And you'll understand why a particular structure is—or isn't—masonry noncombustible.


  • Buildings with exterior walls of masonry—not less than four inches thick, or
  • Buildings with exterior walls of fire-resistive construction—with a rating of not less than one hour, and
  • Noncombustible or slow-burning floors and roofs—regardless of the type of insulation on the roof surface

Advantages of masonry noncombustible construction 

  • Uses floors and roof supported by superior exterior bearing members that provide for stability and are less likely to collapse during a fire
  • Uses materials that don‘t readily burn

Disadvantages of masonry noncombustible construction

  • Uses unprotected steel for interior members of floors and roof, and steel loses strength and becomes less stable and more damageable at high temperatures
  • Uses slow-burning materials that do burn—adding fuel to a fire