Exposure D - Hurricane-Prone Region

[LearningAlways]

I'm hoping someone can shed some light on this. I've asked a couple other engineers but haven't found a solid answer. Exposure D is pretty clear when at the coast and unobstructed but there's a parenthesis in the commentary description that has me wondering. I've looked in the code as to an explanation but haven't found much.

The Chapter 26 commentary shows an image (attached) of Exposure D. The description says Exposure D (except in hurricane-prone regions) with wind flowing over open water for a distance of at least 1 mile. I work in Florida and am in a hurricane-prone region, does this mean there is an exception we should be following? Like does exposure D extends further into the coast, etc.?

Anyone know what that phrase in parenthesis is alluding too?

 

[MegaStructures]

From

https://www.floridabuilding.org/fbc/wind_2010/flyer_wind_january2012.pdf

"Since the first edition of the Florida Building Code, including ASCE 7-98, ASCE 7-02, and ASCE 7-05, in hurricane-prone regions, sites exposed to open water have been classified as Exposure Category C. This was based on research that, at the time, indicated the sea surface roughness in hurricanes increased as wind speed increased. Newer research has shown this not to be the case. The newer studies show the sea surface drag reaches a maximum when wind speeds are between 60 to 80 mph. Additionally, there was some evidence indicating the sea surface drag actually decreases as wind speed increases. In recognition of this research, the use of Surface Roughness D is now required for all water surfaces in hurricane-prone regions including coastal areas. Exposure D will apply where Surface Roughness D prevails in the upwind direction for at least 5000 ft (1524 m) or 20 times the height of the building whichever is greater. More simply put, Exposure D applies where the building or structure is exposed to wind over open water that extends 5000 ft or 20 times the height of the building in the upwind direction."

From the current FBC

Exposure D. Exposure D shall apply where the ground surface roughness, as defined by Surface Roughness D, prevails in the upwind direction for a distance of at least 5,000 feet (1524 m) or 20 times the height of the building, whichever is greater. Exposure D shall also apply where the ground surface roughness immediately upwind of the site is B or C, and the site is within a distance of 600 feet (183 m) or 20 times the building height, whichever is greater, from an Exposure D condition as defined in the previous sentence.

I think the general definition for exposure D closely works for hurricane regions, but there are additional requirements levied for hurricane regions as can be seen in the clippings above