We’ve created a few quick steps that will help any design professional understand how and when to apply an exposure D condition.
1. CONFIRM SURFACE ROUGHNESS DISTANCE AND THE INITIATION POINT OF EXPOSURE D: THE INITIATION POINT (Ip) OF EXPOSURE D OCCURS AT THE POINT ON LAND WHERE “SURFACE ROUGHNESS D” PREVAILS IN THE UPWIND DIRECTION FOR A DISTANCE OF 5000 FEET MINIMUM.
INITIATION POINT (Ip) = SURFACE ROUGHNESS > 5000FT
2. DETERMINE DISTANCE OF STRUCTURE FROM THE INITIATION POINT (Sdist).
3. CONFIRM PRIMARY EXPOSURE D REGION: THE PRIMARY EXPOSURE D CONDITION OCCURS (FOR ALL STRUCTURES) FROM THE EXPOSURE D NITIATION POINT AT THE DIRECTLY EXPOSED COASTLINE AREA, RUNNING INLAND FOR A DISTANCE OF 600 FEET (Dprimary = 600 FT).
IF (Sdist) < (Dprimary) THEN EXPOSURE D APPLIES
4. CONFIRM BUILDING-SPECIFIC EXPOSURE D REGION: A SECONDARY EXPOSURE D CONDITION MAY OCCUR BASED ON THE STRUCTURE ITSELF. TO DETERMINE THE BUILDING-SPECIFIC EXPOSURE D REGION, MULTIPLY THE MEAN ROOF HEIGHT (MRH) OF THE STRUCTURE BY 20 (Dsecondary=MRH*20). COMPARE Dsecondary TO THE Sdist.
IF (Sdist) < (Dsecondary) THEN EXPOSURE D APPLIES
