Area Increase

(Eq 5-3)
Aa = [At + (NS × If)] 
where:
Aa = Allowable area (square feet). 
At = Tabular allowable area factor (NS, S13R or SM value, as applicable) in accordance with Table 506.2. [9500 s.f.]
NS = Tabular allowable area factor in accordance with Table 506.2 for a non-sprinklered building (regardless of whether the building is sprinklered). [9500 s.f.]
If = Area factor increase due to frontage (percent) as calculated in accordance with Section 506.3. [ 0.32 see calcs below)

(Eq 5-5)
If = [F/P - 0.25] x W/30 (Equation 5-5)
where:
If = Area factor increase due to frontage.
F = Building perimeter that fronts on a public way or open space having minimum distance of 20 feet (6096 mm).
P = Perimeter of entire building (feet). 
W = Width of public way or open space (feet) in accordance with Section 506.3.2.

Existing and New Bldg have 258’ that has 30ft of open space perpendicular to those sides of the building.  

F= 108 ft + 75 ft + 75ft = 258 ft
P= width = 75 ft and length = 108 ft; perimeter = (75 x 2) + (108 x 2) = 366 ft
W = (108 x 30) + (75x 30) + (75 x 30) = 7,740 / 258 = 30 ft (Weighted W)

Eq 5-5    If = [(258/366) – 0.25] x (30 / 30) = 0.455 or 45.5%
Eq 5-3     Aa = 9500 s.f + (9500 s.f x 0.455) = 13,822 s.f