Firewalls (Masonry Walls)

UL 2-hour fire-rated Concrete Masonry Unit (CMU) wall assemblies are typically achieved using 8-inch thick hollow or grouted blocks, which provide sufficient thickness for 2-hour protection under ASTM E119 testing. Common assemblies include U901, U904, U905, and U906 .Key factors include aggregate type and equivalent thickness, with 8-inch lightweight block providing 2 hours and medium-weight often requiring grouting.