Solar access
It provided that:[2] When the access and use of light to and for (any building) shall have been actually enjoyed therewith for the full period of 20 years without interruption, the right thereto shall be deemed absolute and indefeasible, any local usage or custom to the contrary notwithstanding, unless it shall appear that the same was enjoyed by some consent or agreement, expressly made or given for that purpose by deed or writing...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.
Its spatial limits are defined by the characteristics of land size, shape, orientation, topography, latitude, and its surroundings.
[5] It guarantees solar access to properties by regulating construction limits derived from the sun’s relative motion.
The goal of that study was to improve the quality of the urban environment by designing buildings that pay attentions to orientations.
[6] In 1976, a research was carried out by Ralph L. Knowles to further develop the concept of solar envelope as a public zoning policy.
Assisted by planning department of the city of Los Angeles, the results of this research were first published in an article called Solar Energy, Building, and the Law.
[6] The most commonly cited law outside the United States is the English Doctrine of Ancient Lights, but there were problems with its application in modern society.
[11] Within the time constraint, for example 9am to 5pm in the winter and 7am to 7pm in the summer, the solar envelope defines the biggest volume that a construction can have to avoid casting shadows off-site.
A solar envelope can be generated for any land parcel during any time interval using the following methods: the heliodon (sun-simulating machine), descriptive geometry, or computers software (e.g Autodesk Revit and DIVA for Grasshopper in Rhino).
[4] Ildefons Cerdà's Eixample of Barcelona is credited as being a good example of an orthogonal town-plan street orientation for increased solar access.
During the winter, every street on the Spanish grid receives direct light and heat sometime between 9AM and 3PM, the six hours of greatest insolation.
It is true that at midday, all streets have shadows; but because of their diagonal orientation, more sunlight enters than if they ran due east-west.
For East and West oriented houses, the solar elevation is lowered to 32°, which reflects the sun’s path across the sky.
[12] Legal experts have suggested that American water law, especially the doctrine of prior appropriation, may offer a more useful precedent for sun rights.
[14] Zoning regulations in Washington DC require that "Any addition, including a roof structure or penthouse, shall not significantly interfere with the operation of an existing or permitted solar energy system of at least 2kW on an adjacent property..."[15] The regulation goes on to define "significant interference" as no more than 5%, and includes the ability of neighbor/developer & solar owner to come to an agreement that allows infringement.
