VOICES | MEASURING DAYLIGHT Keep the British daylight standard with paper-based verification A new European Standard measuring daylight in buildings is too complicated and should be suspended, according to Anglia Ruskin University academics Peter S Defoe and Andrew Thompson. A position not supported by one of the standards authors (see right) T he new BS EN 17037 Daylight in Buildings How was the impact of the change assessed on the includes methods of calculation for design nations existing property? parameters that differ from those in the former standard, BS 8206-2: Lighting for buildings. These The UK BSi committee has accepted that further include view out of windows and access to sunlight, and research is required into how daylight is perceived by it adds glare as an issue to be considered. individuals. Surely this should have been done already? BS 8206-2 was read in conjunction with BRE BR 209 Software providers representing the major systems Site layout planning for daylight and sunlight and CIBSE used by daylight practitioners are currently unable LG10 Daylighting A guide for designers as guidance only, to provide an application to implement the standard but BS EN 17037 no longer refers to these documents. capable of cross-platform validation. So a software-toThe transition to BS EN 17037 represents a software check is not possible for the full calculation fundamental shift in calculation methodology and range and it is impossible to verify results manually. threshold. It is no longer considered appropriate to Minimum fitness appears not to have been calculate a vertical sky component at the window face considered in respect of the Homes (Fitness for and the average daylight factor within the room. The Human Habitation) Act 2018, which came into standard requires daylight to be assessed by a calculation effect on 20 March 2020. This creates a statutory method based on daylight factor and cumulative daylight requirement for properties to be fit for human availability data, or based on the direct prediction of habitation in relation to, among other things, natural illuminance levels using hourly climate data. lighting, ventilation and water supply. Where daylight We believe there are a number of issues with BS EN provision is to be assessed, the official guidance, 17037, including the requirement for specialist software under the Housing Health & Safety Rating System, and the shortage of underpinning research. We are references BS 8206. In practice, any assessment based calling for it to be returned to Draft for development on the BS and compliance will, as a result, be a question status and for BS 8206-2:2008 to be temporarily of technical fact based on the levels stated in the new reinstated until the research, software and threshold standard rather than what was appropriate at the time target levels have been adequately investigated. of construction. Both BS 8206-2 and BR 209 have weaknesses, in that their This standard is unlikely to be useful in advising planning methodologies are based on historical research and simplified authorities on new housing design or impact. Adoption into calculations. However, an advantage is that both are capable of planning policy might even lead to challenge and potential being undertaken or checked using paper-based systems. judicial review of decisions because of the lack of research to The new standard states that calculations based upon the support the adoption. methodologies described must be undertaken using software, Results are still presented in numerical form and/or colour which means the results cant be checked or validated without contours, neither of which informs the stakeholders how the software and 3D modelling. We accept there is a need for a better room will appear at various times of day throughout a year. methodology for assessing daylight before construction, but Obviously, a methodology that shows graphically how the light outputs should be capable of being understood by lay clients and penetrates a room will be an improvement, but it must be capable of being verified independently. Paper verification is low-cost and of being modelled for ease of understanding by lay people. an important safeguard in the planning system when assessing the It is our opinion that, given current computing abilities environmental impact of new massing on adjacent properties. and with further research into actual requirements and into The standard makes no reference to supporting material or any a wide selection of building typologies it would be possible research to justify the assertions made regarding minimum levels to produce models with accurate colour and reflectance of illuminance. The authors pose the following questions: rendering that would enable real-time visualisation of an Where is the BRE concept design property for example, an internal environment. experimental control building where results can be However, it is recognised that the sheer number of verified through research triangulation? calculations for complete analysis would be prohibitive. Which buildings aspired to the standard One solution could be to identify only those rooms with DR PETER DEFOE, FRICS is before implementation and was there postthe least daylight and analyse those, along with a sample an honorary research fellow occupancy evaluation? of others or those that the stakeholders require. at Anglia Ruskin University ANDREW THOMPSON, FRICS is a ARU senior lecturer 28 July 2020 www.cibsejournal.com CIBSE July 2020 p28-29 Daylight debate.indd 28 19/06/2020 17:22