From GridLAB-D Wiki
exterior_floor_area – Used to calculate envelope_UA.
Synopsis
module residential; class house { double exterior_floor_area[sf]; }
Remarks
This is an automatically calculated value, not a variable that the user may set.
It is calculated by:
exterior_floor_area = floor_area * exterior_floor_fraction / number_of_stories
Default
Using all default values:
<math>2500\text{ft}^2 \cdot \frac{1}{1} = 2500\text{ft}^2</math>
Therefore the default exterior_floor_area is 2500 square feet, which equals the default floor_area.