Window sill

A windowsill (also written window sill or window-sill, and less frequently in British English, cill) is the horizontal structure or surface at the bottom of a window.

In these cases, a strip of waterproof and weather resistant material (steel, vinyl, PVC) called a sill pan may be used to protect the wall and shed the water.

[1] A window sill may span the entire width of a wall from inside to outside, as is often the case in basic masonry construction, making it visible on both the interior and exterior of the building.

Conversely, a window sill may only extend from the internal wall structure to the outside and not be visible from the building's interior.

In residential buildings, some people use this latter kind of interior window sill or stool to store houseplants, books, or other small personal items.