The Building Research Establishment has issued a “comprehensive revision” of its document Site layout planning for daylight and sunlight: A guide to good practice (BR 209). Like its predecessor, this 2022 third edition “gives advice on site layout to achieve good sunlighting and daylighting both within buildings and in the open spaces between them”. It is “purely advisory and the numerical target values within it may be varied to meet the needs of the development and its location”.
Daylight
So what is new? Out go the average daylight factor and no skyline/daylight distribution tests as recommended measures to assess the overall amount of daylight in new rooms. Those familiar with the old minimum ADF values for kitchens, living rooms and bedrooms must set this methodology aside. Apart from the continued use of the vertical skyline test, daylight is now to be checked using either of two methods set out in British Standard 17037: 2018 “Daylight in Buildings” (BS EN 17037). Appendix C to the BR 209 guidance summarises the two methods, both of which are more complex than the old.
The first – the illuminance method – is based on target illuminances from daylight to be achieved over specified fractions of the reference plane (a plane at table top height covering the room) for at least half of the daylight hours in a typical year. This requires climatic data for the site location “at an at least hourly interval for a typical year” and is described as “detailed and calculation intensive”.
The alternative method (the daylight factor method) is based on calculating the daylight factors achieved over specified fractions of the reference plane but we are told that “usually a detailed simulation model is still used”. The results have to then be tested against the new BRE recommended daylight targets. Appendix C explains that the guidance in BR 209 is intended to be used with BS EN 17037 and its UK National Annex. BS EN 17037 gives three levels of recommendations for daylight spaces and its Annex A provides values for different room types.
Importantly, the UK NA sets out minimum standards in all UK dwellings. For compliance with the standard, the minimum level should be used. BR 209 warns against very high daylight levels, where summertime overheating (of which more later) can arise. Specified default values are given to be used if none are measured or specified, with maxima reflectance indicated for specific surfaces. Where specific surface finishes are used, appropriate factors for maintenance and furniture should be included.
The guidance is clear that the surfaces utilised in the assessment, as well as its maximum reflectance, need to be presented in the results. Where specific surfaces are relied on either to achieve compliance or near compliance, it may be important to prove the characteristics of the material by reference to the manufacturer’s specification.
Sunlight
The annual probable sunlight hours test has also been replaced for new buildings, though it is retained for assessing impacts on existing buildings. Sunlight amenity is now to be tested on 21 March when a habitable room, preferably a main living room, can receive a minimum of 1.5 hours of sunlight. This is to be assessed at the inside of the window. Sunlight received by different windows serving one room can be counted, but only if the sun lights the windows at different times. Where the positions of the windows are not known, availability of sunlight is to be assessed at points no more than 5m apart, and at a point of 1.6m above ground level. Though the minimum of 1.5 hours is given in BS EN 18037, BR 209 notes that a local planning authority may legitimately seek a different target value for hours of sunlight.
Solar panels
The 2022 edition of BR 209 contains more guidance on photovoltaics. The case of R (on the application of McLennan) v Medway Council) [2019] EWHC 1738 (Admin); [2019] PLSCS 130 established that the potential interference with solar panels is capable in law of amounting to a material planning consideration. In that case, the failure of an officer report to consider this impact led to the quashing of the permission.
Within BR 209, the overshadowing or obstruction of PVs is noted as potentially capable of having a considerable negative impact on performance: where a proposed development of any type is near to an existing solar installation or building it is good practice to try to minimise any loss of solar radiation. Section 4.3 offers new, more detailed guidance on this topic.
Overheating
As in the previous edition, the risk of overheating is referenced and needs to be borne in mind. This is an area which is acquiring increased significance, especially in the context of specialist accommodation for the elderly, where people can reasonably be expected to spend more time inside. The London Plan leads the way by including a policy directed to managing risks to the city from heat (policy SI4), which highlights orientation and shading as key elements of the cooling hierarchy.
Part O of the Building Regulations 2010 took effect on 15 June 2022 but applies only to new residential buildings. It does not apply to extensions added to residential buildings after they are built, nor does it apply to changes of use. The need to comply with the Building Regulations is a material consideration for the designer, just as much as the decision-maker determining an application. What if the need to comply with the Building Regulations resulted in a design that was not BRE compliant? This factor would need to be weighed with other considerations in the overall planning balance.
Practical application
Outstanding applications and appeals which deal with the issues addressed by BR 209 will need to be reassessed against the tests set out within the third edition. Notwithstanding the references within the BRE to the BS document, practitioners will be alive to the fact that adopted planning policies or supplementary planning documents often refer to the BRE guidance: it is this which is to be applied in such cases.
The focus on surface reflectance will lead to pressure to impose conditions on planning permissions informed by these assessments to ensure that the surfaces relied on to show compliance (or near compliance) with BR 209 are used in the final development and thereafter maintained. It is unrealistic to think this can be avoided unless default values are used.
In relation to PVs, most development plan policies that reference the BRE guidance do so in the context of daylight and sunlight and broad residential amenity considerations, rather than energy consumption. However, it has long been noted by decision-makers that reductions in daylight can lead to increased energy consumption and the associated costs. In the context of environmental impact assessment, there is no reason why existing solar panels are not capable of forming part of the wider “environment” which might be the subject of “likely significant effects”. Accordingly, where there are likely significant effects, they will need to be assessed. Scoping opinions and directions will need to consider if these effects should be scoped in or out in the same way as broader daylight and sunlight impacts.
Overall, the task of the developer in juggling a multiplicity of considerations is becoming ever more complex. Planners must grapple with increasingly complex issues. A more holistic approach to optimum energy, daylight and sunlight factors is required at the planning stage. While the numerical assessments need to be identified and considered, the wider context of the development and its location should also be critical to final decisions.
Mary Cook is a barrister and partner and Aline Hyde is a paralegal at Town Legal LLP
The revised guidance is available from BRE Bookshop
