From GridLAB-D Wiki
net_exterior_wall_area – Used to calculate envelope_UA and house_content_heat_transfer_coeff.
Synopsis
module residential; class house { double net_exterior_wall_area[sf]; };
Remarks
This is an automatically calculated value, not a variable the user may set.
It is calculated by:
net_exterior_wall_area = exterior_wall_fraction * gross_wall_area - window_area - door_area
Default
Using default values:
<math>1 \cdot 1633\text{ft}^2 - 244.95\text{ft}^2 - 78\text{ft}^2 = 1310.05\text{ft}^2</math>
Therefore the default net_exterior_wall_area is about 1310 square feet.