BRE – Building Research Establishment
The new BRE guidelines for Daylight & Sunlight 2022 have been amended to incorporate updates from the British Standard for Daylighting in Buildings (BS EN17037) issued in June 2019. The BRE guidelines are widely relied on by planning authorities when assessing proposed new developments for Daylight and Sunlight.
The new guidance recommends the assessment of natural light conditions for all residential planning applications with a fundamentally different approach. It also introduces a requirement to assess other non-residential uses for the first time.
4 Method of assessment
4.1 Daylight calculations for neighbouring buildings
The BRE Report sets out two calculations that should be used for testing the daylight to
existing and neighbouring buildings to a development:
- the vertical sky component (VSC) assessment – the percentage of the total sky that can provide direct light to the centre of the face of the window when neighbouring obstructions are taken into account, and
- the no sky contour (NSC) assessment – the area of a room on a working plane of 850mm above floor level that can receive direct light from the sky through the window. The BRE Report states that: ‘the diffuse daylighting of the existing building may be adversely affected if either:
- the VSC measured at the centre of an existing main window is less than 27% and less than 0.8 times its former value; or
- the area of the working plane in a room which can receive direct skylight (the NSC) is reduced to less than 0.8 times its former value.’
Both of these must be met because the failure
RICS Daylighting-and-sunlighting
WLC Residential Development Guide – text below
Daylight
- New development should not cause an unacceptable loss of daylight to habitable rooms of existing neighbouring properties and all new dwellings must also receive an adequate amount of daylight. For the purpose of this guidance, habitable rooms are defined as a living room, bedroom and dining room. Non-habitable rooms include bathrooms, utility rooms, staircases, halls, landings, etc.
- The orientation and position of windows and the location of gardens in relation to a proposed new development are especially important considerations and new dwellings must be designed with this in mind.
- Technical calculations can be undertaken to determine whether daylighting to existing buildings will be adversely affected, and if there is any suggestion that new housing could cause excessive loss of light or overshadowing of neighbouring properties, applicants may be required to support their proposals. Specific assessment methods are set out in the Building Research Establishment Report Site Layout Planning for Daylight and Sunlight: A Guide to Good Practice 2nd edition by P J Littlefair (2011), demonstrating both before and after circumstances in order to ensure acceptable interior and exterior conditions.
Sunlight
- New development should not cause an unacceptable loss of sunlight to neighbouring properties and their gardens and all new dwellings and their private gardens must also be adequately sunlit.
- Proposals that would result in the loss of sunlight, leading to overshadowing for a significant part of the day, or which would have a visually intrusive impact, will also not be supported. It is an established planning principle that new development should not borrow amenity from adjacent land, and, as a general rule, the greater part of any overshadowing caused by a new building
must be confined to the developers own land. - New dwellings should be constructed to take advantage of sunlight to provide a pleasant living environment and to maximise solar gain. This can be achieved by positioning main living areas, conservatories and rear gardens to generally face south or south-west where practicable.
- It is, however, important to note that while housing layouts should be designed to maximise daylight and sunlight to dwellings, this should not be to the exclusion of other considerations such as privacy or the achievement of more intimate and attractive streetscapes. As in all things, it is a matter of achieving the right balance.