In architecture and construction, the sill refers to the part of the wall (interior or exterior) of a building located between the floor and the window sill.

The height of the parapet is counted from the finished floor to where the flashing begins.[1]​[2]​.

On terraces, balconies and other open elevated structures of a building, it can also refer to the wall or balustrade that is located in the front (low-height external wall, below the open space).[3]​.

It can also refer to a small supporting wall below the window that also serves as decoration for a room.

The word comes from the Spanish ante- and pecho, from the Latin ante- and pectus.[4]​.

In Germany, the minimum height for the private sector is regulated in state building codes and other regulations. This is usually 80 cm for window sills and 90 cm for drop heights over 12 m.[5]​ In other countries (for example, Ireland and the United Kingdom), 90 cm and 110 cm are sometimes required for higher drop heights.