Solar access

Solar access is the ability of one property to continue to receive sunlight across property lines without obstruction from another’s property (buildings, foliage or other impediment). Solar access is calculated using a sun path diagram. Sun is the source of our vision and energy. Its movements inform our perception of time and space. Access to sun is essential to energy conservation and to the quality of our lives.

Solar access is differentiated from solar rights or solar easement, which is specifically meant for direct sunlight for solar energy systems, whereas solar access is a right to sunlight upon certain building façades regardless of the presence of active or passive solar energy systems.

A historical example of Solar access is Ancient Lights, a doctrine based on English law that refers to a negative easement that prevents the owner or occupier of an adjoining structure from building or placing on his own land anything that has the effect of obstructing the light of the dominant tenement. In common law, a person's window on his property receiving flow of light that passed through it for so long a time as to constitute immemorial usage in law, the flow of light became an “ancient light” that the law protected from disturbance. The Prescription Act 1832 created a statutory prescription for light. It provided that:

The goal of using solar access in urban planning is to create well-designed urban districts that assure exposure of buildings' elevations and public spaces to the sun during a desired period of the year. Urban areas that do not consider solar access may cause discomfort inside buildings and on the street, as well as increase energy consumption for lighting and heating, due to the lack of passive solar energy. On the other hand, as a result, buildings without solar access may also have less solar heat gain and thus reduced cooling load.

The solar envelope is a space-time construct. Its spatial limits are defined by the characteristics of land size, shape, orientation, topography, latitude, and its surroundings. Its time limits are defined by the hours of the day, season of the year, and the time interval. In 1976, solar envelope was first proposed by Ralph L. Knowles as a zoning device. It guarantees solar access to properties by regulating construction limits derived from the sun’s relative motion. Buildings within the solar envelope would not shadow adjacent properties during a predefined period of time, usually critical energy-receiving periods during the year. The solar envelope presents the maximum heights of buildings that do not violate the solar access of any existing buildings during a given period of the year. The solar envelope is a way to assure urban solar access for both energy and life quality.

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