10 Jun 2022
The BRE Daylight and Sunlight Report (Site Layout Planning for Daylight and Sunlight: a guide to good practice) has been revised. The guidance contained in the Report has been updated to reflect the changes in the British Standard. It will fundamentally change the way applicants are required to assess natural light conditions for all residential planning applications. It also introduces a requirement to assess other non-residential uses.
The revised BRE Report is a guidance document giving advice on the interpretation of the recommendations given in both British Standard BS EN 17037 and CIBSE guide LG10. The previous British Standard (BS 8206 part 2) was replaced in June 2019 by BS EN 17037.
BS EN 17037 introduces a number of new tests and definitions to the current daylight and sunlight testing practices. The most notable changes are:
The Average Daylight Factor (ADF) and No Sky Line/Daylight Distribution (DD) tests for proposed accommodation are deleted and replaced.
Daylight in proposed buildings is to be assessed with reference to the area of the room achieving target daylight factors. An alternative test using target Lux value is also discussed. Both are valid and either can be used by an applicant. The tests introduce the effects of internally and externally reflected light into the daylight evaluation. Target illuminance testing also introduces time criterion.
Further qualitative tests for View, Sunlight Exposure and Glare are introduced.
The current documents (BRE Report, BS 8206 part 2 and LG10) discuss daylight and sunlight within homes, schools, hotels and hospitals but do not apply guidance to workspace. The new standard applies to the above buildings and additionally, provides guidance for workspaces.
As anticipated the revised BRE Report leaves the current recommendations for effects on neighbouring properties and open spaces untouched. The major changes will be to assessment of proposed developments with the current daylight (VSC, ADF, DD) and sunlight (APSH) tests being superseded by the new tests.
The changes will have a profound effect on the way daylight and sunlight within new development is assessed. Developers, architects and local planning authorities should be aware of the changes and the implications they will have during the design process and in the determination of planning applications.
Daylight within proposed accommodation
The previous BRE Report recommended that daylight within proposed accommodation was tested using the Average Daylight Factor (ADF), Room Depth and No-Sky Line or ‘Daylight Distribution’ (DD) tests. These tests are deleted and replaced with daylight provision which will now be tested through either of two tests. The new tests are undertaken with reference to minimum, medium and high target illuminance values.
The first suggested test assesses daylight factors across a reference plane at 850mm above floor level covering the whole room area. The plane should see the target daylight factor (DTM) achieved across at least 50% of the test plane. For the United Kingdom the target minimum, medium and high daylight factor (D) values are set at 2.1%, 3.5% and 5.0% respectively. For example, as a minimum, rooms should see D values of 2.1% or above across half of their area tested at 850mm above the floor.
The second test applies minimum target illuminance (ET) targets to be achieved across 50% of a reference plane set at 850mm above the floor. These values, 100 lux for bedrooms, 150 lux for living rooms and 200 lx for kitchens mimic the traditionally applied ADF targets. Local climatic data is used and the ET should be achieved for at least half of the available daylight hours (i.e. for 2190 hours per year).
BS EN 17037 Daylight tests summary table:
Sunlight within proposed accommodation
The Annual Probable Sunlight Hours (APSH) tests discussed in the BRE Report are also to be replaced. Under the BS EN 17037 guidance, sunlight amenity is tested on any date between February 1st and March 21st for spaces receiving sun beams (i.e. those facing within 90 degrees of due south). The test determines the possible sunlight duration for that day:
minimum being 1.5 hours,
medium being 3.0 hours, and
high exposure being 4.0 hours.
The assessment is undertaken at a test point on the inside face of the window. Rooms with multiple windows can add the values for each window together where they occur at different times in the day. BS EN 17037 recommends that the at least one habitable room (living room, bedroom, nursery or kitchen) in a whole dwelling should comply with the guidance.
BS EN 17037 discusses the importance of ‘view’ on occupants of assessed spaces. It introduces several criteria that combine to form a view and provides guidance on assessing whether the view is rated as minimum, medium or high. A number of testing methodologies are discussed in the BS and all are used to determine the quality of the view and provide minimum window sizes driven by room size. This guidance can be applied to proposed units and neighbouring buildings.
To assess ‘view’, test points are determined within the ‘utilized’ area of the room. These test points are not fixed and are chosen to represent where occupants are likely to spend much of their time. The test points are used to determine the horizontal sight lines and number of layers of view visible when tested at 1.2 m above the floor level. Additionally, the distance to external obstructions is determined. All of the factors are then assessed to determine the rating of the view.
BS EN 17037 View tests summary table:
BS EN 17037 discusses the effects of overly bright areas or areas where there is a strong contrast between light and dark on the human eye. Importantly the new BS recommends that for areas where people cannot choose their position and viewing direction, protection from glare is provided. The standard discusses a number of tests that can be applied to assess the potential for glare and the effectiveness of the provided protection. In practical terms glare assessment is unlikely to be required in housing as a general rule as occupants can choose to change position or are able to use shading devices (blinds/curtains) to mitigate the instances.
BS EN 17037 changes the tests to be applied when assessing natural light provision within proposed accommodation. The previous daylight tests of ADF and DD/No-Sky Line are deleted and replaced. Sunlight tests are also deleted and replaced. Additional testing for ‘view’ is be introduced.
The revised methodologies are significantly different from the ‘traditional’ approaches to assessing daylight and sunlight conditions for planning. They provide a more accurate assessment of natural light within buildings. The move away from the previous simplified calculations has been brought about by the advances in simulation technology and the need to provide practical guidance for natural light in urban areas.
The changes will have a pronounced effect on the way daylight and sunlight is assessed for all residential planning applications. Developers, architects and local planning authorities will need to familiarise themselves with the new guidance to ensure it is correctly applied in the design of new development and in the determination of planning applications
Lichfields’ Neighbourly Matters team is well versed in the changes and has been using the revised calculations for some time to provide discussion and verification of findings for developments in dense urban areas. We would be happy to discuss the revised calculations and their impacts on natural light testing or can arrange a CPD session covering these new approaches to the assessment of daylight and sunlight.
 Ratio of illuminance received directly or indirectly from an overcast sky at a point on a reference plane to that received by an unobstructed horizontal plane.
22 Jul 2020
The beginning of August 2020 will see the addition of a new permitted development right (PDR) into the Town and Country Planning (General Permitted Development) (England) Order 2015 (GPDO). The new PDR allows two storey extensions to be added to existing residential buildings without planning permission, but subject to prior approval, conditions and limitations (new Part 20 Class A). Other amendments coming into force that day introduce additional prior approval considerations relating to natural light to existing PDRs for changes of use to dwellinghouses.
And on 31 August, new permitted development rights for additional storeys on single dwellings and commercial and mixed use buildings and to knock down a vacant commercial or residential building and replace it with a new residential building will come into force, subject to prior approval, conditions and limitations.
Amongst the prior approval matters for the PDRs for new dwellings achieved by additional storeys or a new building is a requirement to consider both the effects of permitted extensions on the residential amenity of neighbouring properties -including loss of light- and the ‘provision of adequate natural light’ within the newly created dwellings. The latter requirement applies to all habitable rooms within the proposed residential accommodation. This latter requirement now also applies to PDRs for a change of use to dwellings from offices, shops, casinos, light industrial and agriculture (but not storage). The loss of light to neighbouring properties must be considered in prior approval application to extend single dwellings by adding storeys.
At first glance this requirement seems clear enough, however, the wording of the requirement is likely to spark debate on the interpretation of the word ‘adequate’.
Natural light studies have been a feature of planning submissions for proposed residential, student, hotel, educational and other buildings for a significant period of time. Planning officers are quite used to seeing studies based on the current Building Research Establishment (BRE) guidance.
The BRE guidance provides direction on the daylight and sunlight targets to be applied to new accommodation and states that if a room is to look adequately lit it will need to comply with the Average Daylight Factor (ADF), No-Sky Line / Daylight Distribution (DD) and room depth guidance. However, the values used are based on a suburban context and are often not achievable in an urban environment. As such, the results of testing in built up locations often shows that developments may fall short of the guidance and liaison with Planning Officers is needed to determine what values should be considered appropriate.
The conversion of an existing structure often brings with it several limitations, window positions are fixed and internal configurations may be limited by support structures. Add to these restrictions the likelihood that neighbouring structures may be in close proximity and of a significant height and it can be seen that the blanket application of BRE Report guidance would be inappropriate. The limitations brought about by urban environments are discussed in the BRE guidance but clearly defined alternative targets are not provided. It is left to the design team and the local authority to determine / accept revisions to the given guidance.
Some local authorities and the GLA have accepted the inevitable deviation from the BRE Report guidance in urban locations. Both the GLA and the London Legacy Development Corporation (LLDC), for example, have supplied guidance that lower daylight values should be considered as appropriate in given urban situations, however, this guidance mostly refers to the effects a proposed development will have on its neighbours. Conversely, some local planning authorities take the view that the BRE guidance should be strictly applied in all settings.
Currently the determination of natural light within a residential development is undertaken using ADF, DD and Annual Probable Sunlight Hours (APSH) tests. These tests are being replaced, but for the time being are still the ‘go to’ tests. The BRE guidance provides absolute targets but no discussion on what deviations if any would be appropriate in an urban location. As such the determination of what should be considered adequate natural light requires judgement and is a matter of what planning officers and planning committees are willing to accept.
The determination of adequacy is and will inevitably remain a subjective matter and the acceptance of a specific development will continue to depend on the strength of the applicant’s analysis and evidence, and the experience of planning officers. Clearly, where a proposed scheme complies with BRE guidance it will be easy to argue that the natural light is adequate, and small deviations are also likely to cause little discussion. However, where rooms deviate significantly from the current guidance, robust justification will be required and clear discussions will need to be undertaken with officers on the application of alternative tests.
Alternative testing methodologies have been in use for decades but are mostly not understood by planning officers, as they do not form part of the BRE guidance. These alternative tests, often used in BREEAM testing of commercial spaces, EFA guidance on school design and design guidance for Healthcare Buildings are mostly based on climate data and often show the duration of given light levels within rooms either for specific days or as an average across the year. These alternative tests have recently been incorporated into British Standards and the BRE guidance is to be revised to suit, however, there is no indication yet on when or if local authorities will apply the new guidance.
Clearly the determination of adequacy required under the updated GPDO will depend on site specific criteria. However, precedence will be key with officers and natural light practitioners closely following the first applications to see what is accepted.
Lichfields’ Neighbourly Matters team is experienced in undertaking a wide range of natural light studies for new developments, building extensions and property conversions across the UK. This experience and our understanding of alternative assessment methods means that we are well placed to assist developers, architects and local authority officers in navigating prior approval applications through the new GPDO requirements relating to natural light.
For further information please contact Toby Rogan-Lyons