On the interior, there is a window sill, and on the outside, there is a window ledge. In a house or single-family dwelling, there is frequently no distinction. In older buildings, there was a large board at the bottom that was inclined outward to enable rainwater to drain. This is now called a storm window sill. These days, the term "window sill" is generally used to describe the part of the frame below the window pane. It supports the weight of anything that might be placed on it such as plants or baskets. If there are shelves below the window, these would also be called sills. Above the window pane you have two options: a header or a cornice. A header is a flat surface mounted on the wall just under the roofline which contains openings for ventilation and plumbing pipes. A cornice is a decorative element made of wood, plaster, or other materials and applied to the top of a building to provide protection from the weather and to add style to the exterior. It can be flat or shaped with details such as dentils (small projections) or molding (a curved piece of wood, plastic, or metal used to cover and decorate a wall or ceiling). In terms of function, a window sill is basically the same thing as a window ledge. The only real difference is that a window sill must support something heavy, while a window ledge does not have to.