Practical Answer: Keep Your Walls Clean
The simplest reason for using curved window grilles is surprisingly simple: they prevent water damage.
Before the advent of modern building materials and sealants, rainwater would run down the glass and pool at the bottom edge. If the grilles were straight and flush with the glass, the water would pool there and eventually seep into the window frame, causing rot, mold, and structural damage.
The curved shape serves two purposes:
-
This channels water away from the frame. The arch acts as a small gutter, directing water towards the edge where it can safely drain away.
-
This creates a ventilation gap. The outwardly curved strip doesn’t adhere evenly to the glass, allowing air to circulate and accelerating the sill’s drying time.
This simple innovation protected wooden window frames for centuries before modern seals were invented.
