From GridLAB-D Wiki
window_area – Total area of the windows in a house.
Synopsis
module residential; class house { double window_area[sf]; }; object house { window_area value sf; };
Remarks
The window area is used to calculate net_exterior_wall_area, envelope_UA, solar_heatgain_factor, and house_content_heat_transfer_coeff. This is an automatically calculated value, not a variable that the user may set.
It is calculated by:
window_area = gross_wall_area * window_wall_ratio * exterior_wall_fraction
Default
Using default values:
<math>1633\text{ft}^2 \cdot 0.15 \cdot 1 = 244.95\text{ft}^2</math>
Therefore the default window_area is 244.95 square feet.