Floor area of a building refers to the total area of the floors within a building. It is an important metric used in construction and architecture for various purposes such as determining the usable space, calculating construction costs, and complying with building regulations.

The floor area of a building includes all the areas that are covered by the floors, but it does not include certain elements such as sills of doors, areas occupied by walls and pillars, and openings. Let's discuss each of these elements in detail:

1. Sills of doors:
The sills of doors are the horizontal members at the bottom of door openings. They are typically made of wood, metal, or stone and serve as a threshold between two spaces. The sills of doors are not included in the floor area calculation because they are not part of the actual floor surface.

2. Areas occupied by walls and pillars:
The floor area of a building does not include the areas occupied by walls and pillars. Walls are vertical structures that divide or enclose spaces within a building, while pillars are vertical structural members that provide support. Since walls and pillars occupy space vertically and do not contribute to the floor area, they are not included in the calculation.

3. Openings:
Openings such as windows, doors, and skylights are not included in the floor area calculation. These openings provide access to the exterior, allow natural light and ventilation, and enhance the aesthetic appeal of the building. However, they do not contribute to the actual floor area and are therefore excluded from the calculation.

In summary, the floor area of a building does not include the sills of doors, areas occupied by walls and pillars, and openings such as windows and doors. These elements are excluded from the calculation because they are not part of the actual floor surface and do not contribute to the usable space within the building.