A building is green if it takes steps in its design and materials to minimize its impact on the environment and encourage sustainability. Nothing built by humans will ever be entirely neutral, but there are many ways to make our impact more sustainably.
In terms of materials, a builder can check on the sustainability of the resources used to make them. For example, if wood is used, it could be determined if the wood is sustainably sourced. In other words, are new trees planted when others are harvested? In addition, the process of extracting some resources has a particularly negative effect on the environment. These, like materials made from petrochemicals, should be avoided.
Many construction materials can be recycled or repurposed for other uses. Glass and stone, which aren’t necessarily considered sustainable materials, can both be reused. Carpets can be made using recycled materials.
Beyond materials, though, the primary function of a building can be made more sustainable. Buildings can use energy-efficient lighting, for one, as well as energy-efficient appliances and electronics. Toilets and sinks can also be more efficient with water use.
One way of making a building greener that is becoming pretty common is using solar power panels on the roof or even on the sides of a building. The generated power offsets the power being used by the building, reducing its carbon footprint.
Less common is the idea of a living roof. On a living roof, foliage is planted, sometimes even a full garden. Some designs go so far as having beehives. The idea is to help the surrounding ecology as much as possible. A living roof can also make a building more energy-efficient by moderating the outside temperature of the building. Even the sides of buildings can be turned into hanging gardens.
Green buildings generally take into account the health and safety of the people inside them as well. Air quality and circulation are taken into consideration. Toxic building materials are excluded from use.
The overall point of a green building is to consider how a building can have a positive impact on the environment and the people within the building instead of a negative one.