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 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 path

Sun path refers to the apparent significant seasonal-and-hourly positional changes of the sun as the Earth rotates, and orbits around the sun. The relative position of the sun is a major factor in the heat gain of buildings and in the performance of solar energy systems...

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Solar access is differentiated from solar rights or solar easement

Solar Easement

A solar easement is a right, expressed as an easement, restriction, covenant, or condition contained in any deed, contract, or other written instrument executed by or on behalf of any landowner for the purpose of assuring adequate access to direct sunlight for solar energy systems.- Features :A...

, 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.

History

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 of 1832 created a statutory prescription for light. It provided that:

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...

UK Statute Law Database

UK Statute Law Database

The UK Statute Law Database is the official web-accessible database of the statute law of the United Kingdom, hosted by The National Archives. It contains all primary legislation in force as of 1991, and all primary and secondary legislation since that date; it does not include legislation which...

Solar access in urban planning

The goal of using solar access in urban planning is to create well-designed urban districts that assure expore 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.

Solar envelope

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. The solar envelope regulates development within imaginary boundaries derived from the sun's relative motion. Buildings within this container will not overshadow their surroundings during critical periods of the day and year.

The influence of street orientation

Ildefons Cerdà

Ildefons Cerdà

Ildefons Cerdà i Sunyer was the progressive Catalan Spanish urban planner who designed the 19th-century "extension" of Barcelona called the Eixample.-Biography:...

's Eixample

Eixample

The Eixample is a district of Barcelona between the old city and what were once surrounding small towns , constructed in the 19th and early 20th centuries....

 of Barcelona

Barcelona

Barcelona is the second largest city in Spain after Madrid, and the capital of Catalonia, with a population of 1,621,537 within its administrative limits on a land area of...

 is credited as being a good example of an orthogonal town-plan street orientation for increased solar access. By rotating the grid to a 45 degree angle from southernly orientation, the morning and afternoon sunlight is able to penetrate into the urban fabric more than in a north-south oriented grid. The so-called "Spanish grid" was also applied in Los Angeles, though in newer parts of the city a north-south grid was used. The Spanish grid is advantageous regarding street qualities of light and heat. 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

Insolation

Insolation is a measure of solar radiation energy received on a given surface area in a given time. It is commonly expressed as average irradiance in watts per square meter or kilowatt-hours per square meter per day...

. 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. In summer, the advantage of the Spanish grid is that shadows are cast into every street all day long, creating a more comfortable environment in hot climates, with the exception of a short period during mid- morning and mid-afternoon when the sun passes quickly over first one diagonal street and then the other.

The Netherlands

In the Dutch building codes, the principal façade of houses must receive 3 hours of direct sunlight between the dates of 21 March and 21 September, the vernal point and autumnal points of the equinox. when the solar elevation is about 38°. For East and West oriented houses, the solar elevation is lowered to 32°, which reflects the sun’s path across the sky .

United States

Legal experts have suggested that American water law, especially the doctrine of prior appropriation, may offer a more useful precedent for sun rights. They point out that both sunlight and water are used rather than captured and sold; both may be consumed, but both are renewable. In addition, there is an equivalence between upstream and downstream in water law and the geometry of solar shadowing. But, like the Doctrine of Ancient Lights, there are problems with the application of water law. At the moment, Solar access laws are usually “voluntary,” meaning that a solar owner cannot require that their neighbor agree to a solar easement.

State of Massachusetts

State law provides a solar access permit, and also provides for solar access in zoning ordinances, including the regulation of planting and trimming of vegetation on public property to protect solar access.