BS EN 17037:2018 Daylight in Buildings – A Critical Review

The new European Standard measuring daylight in buildings is too complicated and fails to adequately safeguard the minimum fitness standards for natural light needed by residential tenants via the provision of a practical calculation solution.

By Dr Peter S. Defoe PrD(BE) DipArb FRICS FCIArb MCQI CQP and Andrew D. Thompson CEnv FRICS FCInstCES FHEA Anglia Ruskin University

The new Daylight in Buildings standard BS EN 17037:2018, almost immediately attracted criticism from daylighting specialists and the research community.

Prior to the publication of this new standard, the UK used BS 82062:2008, the code of practice for daylighting, giving recommendations for daylight design in buildings – including electric lighting design when used in conjunction with daylight and this was supported by BR209 Site layout planning for daylight and sunlight – a guide to good practice. However, this new standard BS EN 17037 deals exclusively with natural daylight and sunlight and it includes methods of calculation for design parameters that did not feature in BS 8206-2 meaning that the domino effect of this change is that housing fitness standards, planning design controls and associated environmental accreditation schemes based on BS 8206-2 have lost the source reference standard. Whilst both BS8206-2 and BR209 have a weakness within their methodologies which are based on historical research and simplified calculations. This manual approach can also be an advantage is that both traditional methods are capable of being undertaken or checked at low cost using only paper-based systems via basic measurement methods. Whilst most practitioners at advanced stage now employ computer-based technologies to model buildings and to undertake the calculations the complexity of the property market is such that daylight awareness needs to be understandable to non-expert practitioners. Landlords, Property Managers, Local Authority Officers and concerned property owners need an accessible and low-cost solution for first stage assessment.

While most parties agree that there is a need to have a better methodology for assessing the performance of daylight within a building prior to construction, they also believe that it is necessary to ensure that any output is capable of being understood by lay clients and of being verified independently.

Neither of these is possible using this new standard. The capacity for paper verification is felt to be an important safeguard for any methodology used in the public planning system. The paperbased approach proving a low-cost simple verification for Local Authority Planning and Environmental Health Officers needing to assess if a property was unfit for human habitation. A strong public policy benefit therefore exists for any daylight calculation to be capable of non-computer verification or to have a first stage non-expert assessment step.

Daylight is a vital feature in the adequacy of living accommodation. Any standard must therefore be capable of considering design that is environmentally positive, as used in design accreditation schemes, whilst equally being robust when considering minimum fitness standards.

This issue of minimum fitness appears not to have been considered from the legal enforcement perspective nor in respect of the Homes (Fitness for

Human Habitation) Act 2018 which came into full effect on 20th March 2020 and was already binding on all new leases agreed since 20th March 2019 amending the Landlord & Tenant Act 1985. Under the former BS8206:2 a Surveyor/ Housing Officer could in one inspection gather via tape and Abney Level all the basic measurement data necessary to calculate the Average Daylight Factor (ADF). A practical answer to a housing fitness concern linked to daylight quality could therefore be assessed by a non-expert practitioner within a half hour to one hour timeframe if this was the housing officers first attempt to assess daylight in a standard size residential room.

Under the BS EN 17037 the new calculation requires a 3D point cloud data scan undertaken by a Land Surveyor, the purchase of both AutoCAD and supporting specialist software, advanced CAD skills training and is a technically demanding task. Justified if undertaking assessments for hundreds of rooms in a major development context but wholly disproportionate for most established housing rental situations or home extensions. In addition, upon enquiry, a representative of the BRE has confirmed that they have concerns regarding the use of the new standard for the following reasons:

The 500mm perimeter used in the sDA calculation is not defined sufficiently to eliminate ‘massaging’ to improve results in rooms particularly those with awkward shapes. (see Image 2)

Glare calculations can take an hour per spot. There is no benefit from something so complex

The Standard was published about one year before any software became commercially available, as a result, software providers have had to resort to emails for clarifications. Surely the standard should have been sufficiently

Typical sDA CAD Image

specific bearing in mind that it is not possible to do the task manually. How do we know that correct interpretations have been applied in all cases?

The climate data files available are very limited for the UK and it has been suggested that most are old and/ or have been extrapolated. In fact, The climate data files issue came out in preparation of the National Annex; and, as can be seen in table NA5, London Gatwick is stated to have a lower diffuse illuminance than Belfast and the same as Aberdeen, which is not likely. The problem may be that climate data files are not selected to be typical daylight years but are predominantly based on other criteria such as degree days.

Other issues raised with the BSi Committee include:

The BS EN 17037:2018 standard uses a reference plane at 85 cm, why? It has been suggested that this is possibly relating to research undertaken in US schools; however, citation cannot be provided. However, if this point is accepted then this appears to create further problems for the BSi Committee in terms of justification of the definition figures. When critical reading is undertaken, and the working plane dimension is cross referenced to the key table height dimension recommendations across other BSi published standards the figure 85cm cannot be defended. The furniture size in UK Educational establishments is set by BS EN 1729-1:2015. This is nearer to 75cm and this would result in slight improvement in results and this is not stated. What then if we ignore educational use and look to commercial office furniture, this triggers BS EN 527-1:2011 Part 1: Dimensions, in order to defend the recommendation the population of the UK would need to be replaced with that typical of Sweden! But still this extra height would only get the dimension to 84.2 cm. The UK h1 is defined as 80cm. Remember we are discussing errors in the authoritative standard dimensions, in an industry standard, dimensional figures matter.

The Homes (Fitness for Human Habitation) Act 2018 establishes a statutory fitness requirement for properties to be fit for human habitation and, whilst this concept is not new, the historic legal cap that made the right previously unenforceable by most tenants has now since 20th March 2020 been removed. When considering fitness of a house or dwelling the legislation expressly requires that regard shall be had in relation to Natural Lighting.

Where the daylight provision is to be assessed, under the above requirements, then the official guidance, under the Housing Health & Safety Rating System, historically required an assessment based on the former British Standard. Should the Courts direct that compliance is now to be assessed against BS EN 17037 the cost implication of tenant challenge could lead to Landlord/Tenant dispute fees greater than the typical £951 rental value of a property (HomeLet Rental Index). This will directly impact on a tenant’s rights to seek redress under the assessment of fitness for human habitation and a Landlords willingness to defend against a spurious claim. The issue is therefore whether the new UK standard for natural light makes it more likely that a property will be deemed unfit due to the impractical nature of the new solution.

Design teams involved in residential schemes now need to be extremely careful in client design advice as a tenant in the Private Rental Sector (PRS) now has a legal right to a higher design standard than an Owner/ Occupier. Whilst at major design stage the cost/benefit of a full technical assessment could be justified this removal from a designer of an easy to understand manual check means that design checking for natural light adequacy will be pushed further down the RIBA stages of works remote from early stage consideration.

Clearly a new standard on natural light has far reaching implications and it is reasonable to expect that such an important document has been considered carefully and is grounded in robust research. This is important for two reasons, firstly because the standard is used by Local Authorities when considering the adequacy of new development designs in both the planning and environmental context. The ripple effect of this use being that Developers and the associated stakeholders and designers will be mindful of the standard requirements, if the standard gains a reputation for being expensive, impractical and unfriendly for decision makers the worst outcome is that it is ignored!

Secondly the application to existing buildings as a benchmark standard underpins the environmental accreditation systems of BREEAM, the Home Quality Mark and the RICS SKa Environmental Accreditation systems for credits under the natural light requirements. These systems of accreditation have both design and post design evaluation stages such that a pure software only solution makes post design inspection evaluation impractical as impossible without a full new exercise.

Typical VSC Image using BR209

The former standard BS 8206-2 was read in conjunction with BRE BR209 Site layout planning for daylight and sunlight and CIBSE LG10 as guidance only, but the launch of BS EN 17037 directly impacts on the recommendations of these other technical documents due to the withdrawal of BS8206-2:2008. The new standard can no longer be interpreted as guidance and cannot be incorporated into BR209 but BR209 continues to reference a standard that no longer exists. This situation will be addressed in the BRE review of BR209 with the potential outcome that the BRE could simply reclaim the ADF calculation. This is perfectly within their right as the UK ADF method is a product of the original Building Research Station in World War II as an emergency solution to aid factory design. The well documented research evidence base for the use of the ADF could, without fuss, allow BRE to publish an updated 3rd Edition of BR209 simply via the removal of any reference to the British Standard. This would for planning and environmental purposes be the simplest BRE solution.

The technical transition from the former BS8206-2 into the new BS EN 17037 represents a fundamental shift in calculation methodology. On balance, once one moves away from the small scale and practical survey assessment requirements, the new standard at advanced calculation level has many positive features once the technical study is a fully 3D computer model assessment exercise. In a practical system society needs both a first step manual approach for which the ADF is a well understood UK solution as well as a more advanced assessment tool. The retention of the ADF/VSC (see image 3) and APSH as the first step for appropriate schemes when a low-cost solution has holistic benefit as it results in an immediate practical solution. Whilst technology and phone applications could in the medium 5-10 year period evolve such that the need for manual verification is fully removed, after all many mobile phones now have noise, lux and a room measurement scanner, this is still the future and society needs to transition to that point of change.

Daylight and Health

The importance of daylight to health is now believed to be established however the research community is still in debate as to the level of adequacy required for pure health purposes. BS EN 17037 makes no reference to works such as “Daylight and Health: A review of the evidence and consequences for the built environment” MBC Aries, MPJ Aarts and J van Hoof, (2015) and whilst expressing target lux levels these are confused as both minimum fitness levels and environmental best practice recommendations. The same lux value cannot be both the minimum necessary for basic habitation fitness and the perfect design level for award winning schemes without designing to the minimum culture. This problem can be traced to the lack of research undertaken to justify the new lux level standards. Where is the BRE concept design property i.e. an experimental control building where results can be verified through research triangulation and reviewed by researchers to explore the evidence of the improvement in design standard? These properties have existed and are well documented to support the historic BRE ADF method and if health benefits are to be critically monitored and assessed to consider merits of levels should have been established before radical change. There is a lack of evidence as to which UK designed buildings aspired to this new standard before implementation – and was there any post occupancy evaluation assessing the merits of change? How was the impact of the change assessed on the nations’ existing property? Where is the BSi economic cost benefit analysis to support this expensive change on industry and property users? No research data based on the national stock condition survey to assess this change impact can be found, so was the impact socio-environmental impact of the system change ever assessed by the BSi before this was imposed? Do BSi have any idea on the scale of properties that have now been deemed unfit for human habitation due to the adoption of this new standard. As this is a new test of fitness especially where none previously existed. Moving to the health qualities of sunlight being beneficial the traditional thinking has been abandoned in BS EN 17037. Historical wisdom has been that for health that sunlight entering a room through glazing would not be the direct source of any benefit as direct skin radiation contact was required. Whilst sunlight is recommended within buildings for other design and environmental purposes the sunlight directly was not considered as a pure health benefit. This is important in spatial planning as the vital role of outdoor amenity space is justified due to the society need for access to sunlit spaces. Destroy this link and the argument in development for sunlit gardens and amenity balcony space is also removed, so claims without any research base need be challenged as otherwise the society risk is the loss of areas of amenity space currently considered vital. Established research, such as that cited by M Nathaniel Mead in the Benefits of Sunlight: A Bright Spot for Human Health (EHP 2008) state that it is only that affect derived from being outside the buildings envelope where, for example, the effects of rickets are mitigated by exposure to sunlight that has a direct health benefit.

This article has highlighted the argument for BS EN 17037 to be returned to “Draft for Development (DD)” status and the temporary reinstatement of BS8206-2:2008 until such time as the research, has been adequately investigated and the methodology provides for both low cost first stage assessment that then evolves to the more complex full 3D Survey and Computer model assessment when appropriate for design circumstances, litigation or environmental complexity.

Dr Peter S. Defoe PrD(BE) DipArb FRICS FCIArb MCQI CQP and Andrew D. Thompson CEnv FRICS FCInstCES FHEA Anglia Ruskin University

Acknowledgements

The Authors would like to acknowledge the technical support provided by MBS in providing access to the daylight software and modelling used to prepare this article.

References

BS EN 17037: 2018 Daylight in Buildings, BSI BS8206-2:2008 Lighting for Buildings, BSI (withdrawn) BS EN 527-1:2011 Office furniture – Work Tables and Desks Part 1: Dimensions

BS EN 1729-1:2015 Furniture – Chairs and tables for educational institutions Part 1: Functional dimensions

BR209 Site Layout Planning for Daylight and Sunlight a Guide to Good Practice 2011 published by BRE Homes (Fitness for Human Habitation) Act 2018 Chapter 34 Housing Health & Safety Rating System (England) Regulations 2005 BREEAM, (breeam@bre.co.uk) Home Quality Mark (www.homequalitymark.com) HomeLet.Co.uk, 2020. What is the average rental value in the UK, June 2020, online access on 21 July 2021 https://homelet.co.uk/homelet-rental-index RICS SKa https://www.rics.org/uk/about-rics/responsible-business/ska-rating/ LG10/14 Lighting Guide 10: Daylighting – a Guide for Designers – LG10: 2014 Daylight and Health: A review of the evidence and consequences for the built environment, MBC Aries, MPJ Aarts and J van Hoof, (2015). The Benefits of Sunlight: A Bright Spot for Human Health, M Nathaniel Mead, (EHP 2008)