What is Sun on Ground?
Sun on Ground (SOG) is a measure of the maximum duration of time that sun can reach a point at ground level. Unlike APSH testing it does not account for the presence of clouds as clear skies are assumed in all testing.
What is SOG used for?
Within the BRE Guide SOG is used to assess both the adequacy of sunlight amenity within proposed outdoor recreation spaces and also the impact on neighbouring gardens and parks.
What do you include in SOG testing?
According to the BRE SOG testing should usually be carried for all open spaces where sunlight is required including:
- gardens, such as the main back garden of a house or communal gardens including courtyards and roof terraces
- parks and playing fields
- children’s playgrounds
- outdoor swimming pools and paddling pools, and other areas of recreational water such as marinas and boating lakes (the daylight and sunlight effects on permanent residential moorings may be assessed using the methods in sections 2.2 and 3.2)
- sitting out areas such as those between nondomestic buildings and in public squares
- nature reserves (which may have special requirements for sunlight if rare plants are growing there).
Where and how is SOG measured?
SOG is measured at an array of test points which cover the full extent of the open space under consideration.
SOG testing is always carried out as a desktop study. While it is possible to calculate SOG using graphic based manual calculations it is more typical nowadays for this testing to be carried out using computer simulations.
Impact testing is carried out by predicting SOG levels across sensitive for qualifying open space in the existing scenario (with existing buildings on the development site) and then again with the proposed development in place.
What is an acceptable level of SOG for proposed open spaces?
According to the BRE an outdoor recreation space will appear adequately sunlit throughout the year if at least half of its area is capable of receiving at least two hours of sunlight on the 21st of March.
How is the impact on neighbouring outdoor spaces determined?
According to the BRE a loss of sunlight is likely to be noticed within an existing neighbouring outdoor recreation space if the area of the open space that is capable of receiving direct light from the sun is both less than 50% the open spaces total area and also less than 0.8 times its former value.
How should the results of SOG testing be interpreted?
According to the BRE the assessment of impact will depend on a combination of factors and there is no simple rule of thumb that can be applied. The BRE Guide advises that the magnitude of the departure from advisory minimums, the sensitivity of the receptor to loss of light and the existence of mitigating factors are all aspects that need to be considered when attempting to determine the significance of an identified impact.
Beyond the guidance provided in the BRE Guide (which states that “the advice given here is not mandatory”) it is important to recognise that in most planning jurisdictions even significant impacts can be deemed acceptable in circumstances where a countervailing planning objective can be articulated.
Should trees be included in SOG testing?
According to the BRE, trees and shrubs are typically not included in this type of testing. One exception to this rule relates to a dense belt of evergreen trees which the BRE advise should be accounted for in calculations.
Does SOG analysis have any shortcomings?
SOG testing provides a simple indication of the proportion of an outdoor area that does not experience persistent shadow on a specific test day. It is assumed that the results obtained for a test day on the 21st of March provide an indication of the average level of overshadowing that will register throughout the year, however this is not always the case.
To test for this possibility it is instructive sometimes to run impact testing for every day of the year in order to identify a truer prediction for average overshadowing.
