Fire Resistive Construction

This Construction Brief will give you an overview of ISO's Construction Class 6 — fire resistive construction. When you've completed this course, you'll know what an ISO report means when it says a building is fire resistive construction. And you'll understand why a particular structure is — or isn't — fire resistive.



  • solid masonry, including reinforced concrete not less than four inches thick
  • hollow masonry not less than 12 inches thick
  • hollow masonry less than 12 inches thick, but not less than eight inches thick with a listed fire-resistance rating of not less than two hours
  • assemblies with not less than a two-hour fire-resistance rating

The exterior bearing walls and load-bearing portions of exterior walls must be of noncombustible materials or of masonry, but exterior nonbearing walls and wall panels may be slow burning, combustible, or with no fire-resistance rating.

Solid Masonry

Solid masonry example

Hollow Masonry

Hollow masonry example

Exterior Walls of Noncombustible Materials

Exterior walls of noncombustible materials