Building Footprint and Sustainable Sites
The building footprint is the projected area on which the building is located. It includes
- Size of building
- No. of floors
- Configuration of building
- Building’s orientation – how the building faces the sun, street, and any other views.
The two significant aspects are the floor area and surface area.
The floor area of a building impacts energy and material use. For ex. more material is needed for a larger building to build the structure.
A smaller building with reduced room sizes and increased occupant density use lesser materials and energy use.
The exterior surfaces on all sides that are in direct contact with outdoors, is the surface area.
The surface area is an essential factor in determining a building’s energy efficiency, heating, and cooling requirements.
The ratio of a building’s surface area to its floor area ( area ratio) determines the energy usage of a building. The larger the area ratio, the more the building uses energy for heating and cooling purposes.
Using simpler shapes like squares and rectangles for a building’s footprint utilizes less energy than using complex shapes such as L-shape /U-shape/Courtyard.
Building elements such as protrusions, cantilevers, dormers, etc., all that adds to the area ratio, also impact the energy use of a building. The ceiling types also affect the floor area ratio. Flat ceilings have smaller area ratios compared to vaulted/cathedral ceilings.
The no. of stories, a building comprises also determines the area ratio has its impact on energy use. The area ratio decreases as the number of stories increases.
However, as buildings get taller, two unrelated factors can work against the energy savings delivered by lower area ratios: The loss of protection against wind by trees or adjacent buildings and the increase of stack effect, which occurs as the buoyancy resulting from temperature differentials drives air up through a building in winter.
Strategies to Minimize Area Ratio:
- Reducing floor-to floor heights.
- Avoiding high ceilings.
- Using Row-building arrangements
- Combining multiple smaller buildings into a single larger building.
- Providing optimum no.of stories.
- Deeper spaces relative to outside walls.
- Minimizing surface complexity.
Orientation affects how much solar gain is captured for useful heat in winter, and how much cooling is required due to unwanted solar gains in summer. It also affects how much air flows through a building due to differences in wind pressure.
For a square building:
- If windows are placed on one wall only, the best wall to place windows is the south wall.
- For windows on both sides, the placing the windows on north and south wall lowers energy usage when compared to placing them on east and west sides.
- Buildings having windows on adjacent walls should orient them south and west or south and east.
For a Rectangular building:
Rectangular buildings having windows evenly distributed on all four sides should be oriented along an east-west axis.