A structure with no windows has no apertures in its facade for admittance of light or views from outside, unless the light or views come through glass doorways. The structure may however have skylights, ventilation, doorways, connections to other structures, or other openings in its roof or facade which do not normally constitute windows.

Skylights and glazed doorways do not by themselves prevent this classification. Ventilation openings and connections to other structures are also allowed when they do not constitute windows.

Unglazed window openings remain windows for this purpose even without glass. The absence of glazing alone does not establish a windowless structure.