A parapet is. Historically, parapets were utilized on castles as security during conflicts. Modern uses include preventing fires from spreading and as ornamental architectural elements.
CNU LEED AP, kenny Craft
Assessing the outside walls upward and beyond the roof, a parapet can function as a railing for rooftop decks.
This parapet is perforated. Castles either staggered the height of the parapet (crenelated) or perforated the reduced wall to provide a safe place to fire weapons from.
Schwartz and Architecture
Wooden eaves in urban areas can disperse fires easily. A parapet can enclose the roofing and slow the spread of fire.
Parapets also function as a barrier to keep occupants securely in and stop things from falling on passersby below.
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Vinci | Hamp Architects
The interior view of a parapet exemplifies how it protects the house within.