PURPOSE: To promote ventilation efficiency of a loft by providing parapet copings having slits to connect the outside and the loft to parapet sections of a flat roof so that an air-inlet side becomes positive pressure and that an air-outlet side becomes negative pressure.

CONSTITUTION: Parapet copings 6a and 6b are provided to the eaves part having no eaves of a flat roof and, at the same time, slits 7a and 7b connected to a loft 3 are provided between copings and external walls. Air flowing from the slit 7a on the windward side flows out of the slit 7b on the lee side. According to the constitution, even in the case of gentle wind, the ventilation of the loft can be made.