Many people probably think “ignition-resistant” is better than “combustible,” but not as good as “noncombustible.” That would be an accurate assessment. The California Building Code defines ignition-resistant in a specific way – based on meeting a minimum flame spread rating after the material has been subjected to a specified weathering procedure. A material labeled ignition-resistant has passed this test. This ignition-resistant definition is based on the International Building Code requirement for exterior fire-retardant lumber and plywood. An example of an