Can 6" masonry be used to satisfy the impact resistance criteria in Florida?
The FBC, 6th edition, Building, Section 1626.4.1 allows for 8" hollow masonry to meet the impact criteria for the HVHZ (Dade and Broward). Although there is no mention of 6" masonry 1626.4.4 allows for 2" of reinforced concrete to meet the requirements also.
Common sense would grant that solid grouted 6" masonry is going to perform better than 2" of poured concrete but again it is not mentioned directly.
That being said, FEMA P-320 Safe Room Const Plans specify 6" masonry with a #5 bar in a grouted cell at 16" o/c.
The more stringent FEMA P-361, Safe Rooms for Tornadoes and Hurricanes, 3rd Ed, March 2015 allows solid grouted 6" masonry with a #4 bar at 32" o/c.
As a side note, we plan to submit a code change to include solid grouted 6" masonry in the "deemed to comply" list under 1626.4 in the 7th Edition FBC. It is not currently listed simply because the issue of its use rarely comes up.
In summary, I can see no good reason why a building official would reject solid grouted 6" masonry as specified in P-361 as being acceptable for missile impact requirements in the HVHZ.
Don Beers, PE, GC
Jerry Painter, FASTM