Why do some window grilles have a curve at the bottom?

The curve at the bottom of some window grilles, often referred to as “potbelly grilles” or “window belly bars,” serves a combination of purposes, primarily related to security and functionality. Here’s a breakdown:

• Enhanced Security:
  • The curved or bulging shape makes it more difficult for someone to gain leverage to pry the grille open. This design adds an extra layer of security, deterring potential intruders.  
• Accommodating Flower Boxes:
  • The curve can provide a space to rest or support flower boxes, allowing residents to add greenery and decoration to their windows.
• Historical and Architectural Style:
  • In some cases, the curved design is simply an architectural feature, reflecting a particular style or period. This is often seen in older buildings, especially in urban areas.  
• Air Conditioner Accommodation (in some cases):
  • While not the primary purpose, in some situations, the curve might offer a bit more space for accommodating certain types of small air conditioning units. However, this is heavily dependent on the size of the curve, and the size of the AC unit.

Essentially, the curved design is a blend of practical security measures and aesthetic considerations.