Masonry Noncombustible Construction

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