June 2022 saw the publication of the latest BRE guidelines on daylight and sunlight. In this article, Katie Harley and Gordon Ingram reflect on the unprecedented challenge of applying these sensibly in an urban environment – and why formal adoption of the recommended two-stage approach is the answer.
In terms of addressing impacts on neighbours, the new guidelines are broadly similar to the previous iteration in 2011. However, they are now much more stringent with regards to the internal environment of a proposal.
With the introduction of the median daylight factor (MDF) and climate based (Illuminance) methodologies to assess the daylight amenity within new residential accommodation, it is going to be more challenging to achieve suggested targets within proposed schemes even with the flexibility afforded by the BRE’s UK Annex which brings the minimum indoor lighting levels in line with the previous targets in the British Standard. The annex was created in recognition that the recommended light levels may not be achievable for some dwellings with significant external obstructions i.e. dense urban environments. In short, the annex recognises the national need to increase urban density to deliver much needed housing.
There is no straightforward answer to the new guidelines, only that technical impact alone should not determine the outcome. Decision makers must look at wider contextual considerations in order to arrive at a balanced planning judgement in the future.
GIA recommends a two-stage assessment, where technical impacts and wider contextual considerations are considered together, when examining the overall impacts of a proposed scheme upon daylight and sunlight.
Although yet to be enshrined in planning policy, this is an approach that has already been endorsed by the Planning Inspectorate and High Court and successfully used in several appeals including the Whitechapel Estate, Buckle Street and Goldsworth Road in Woking.
The formal adoption by policy makers is the next step to ensure a deeper analysis and consistent approach to the consideration of daylight and sunlight matters.
So, how do the new guidelines differ from the 2011 version?
In terms of daylight, the new guidelines remove the average daylight factor (ADF) form of analysis and introduce a new methodology called the MDF. This assesses the daylight distribution in a different way within internal environments. An alternative assessment, known as Illuminance, considers climate-based data in its methodology. The new guidelines do not consider it appropriate to use MDF or Illuminance in relation to neighbours and therefore the existing vertical sky component (VSC) and no skyline (NSL) methodologies remain the status quo.
Turning to sunlight, the methodology used when assessing impacts to existing buildings annual probable sunlight hours (APSH) remains as per the 2011 guidelines. In relation to the assessment of new development however, the guidance has changed, requiring at least a minimum of 1.5 hours of sunlight in one room per unit on 21st March (spring equinox).
What are the implications of these new guidelines?
The introduction of the MDF / Illuminance methodologies means that it will be more challenging to achieve the suggested targets within proposed schemes, even with consideration of the BRE’s UK Annex which allows for flexibility in dense urban environments.
Clearly there is not going to be any straightforward or binary answer to the predicaments of the new guidelines. Therefore, decision makers will need to look at wider considerations rather than simply the technical impact of any proposal upon its immediate environment.
What is the Two-Stage Approach?
The two-stage approach is where both technical impacts and wider contextual considerations are considered together. It stems from the High Court decision on the application of Melanie Rainbird and the London Borough of Tower Hamlets Council (Rainbird, R (on the application of) v The Council of the London Borough of Tower Hamlets  EWHC 657), commonly referred to in the industry as “the Rainbird judgement”.
In 2017, planning permission was granted for a scheme in the London Borough of Tower Hamlets. The permission was later quashed following a judicial review as the judge considered that the local authority had not fully considered the BRE guidelines criteria as part of its evaluation at both officer and planning committee stage.
Highlighting the particular Tower Hamlets policy around daylight and sunlight, the judge stated that a daylight and sunlight assessment “requires consideration of two questions about the impact of a proposed development on the sunlighting and daylighting conditions of surrounding development:
- whether or not it would result in the material deterioration of those conditions; and
- whether or not any such deterioration would be unacceptable.“
Whilst this legal judgement refers to a specific policy in the (now replaced) Tower Hamlets Local Plan in relation to daylight and sunlight amenity, it offers the opportunity for a more thorough examination of the daylight and sunlight implications of any new development. If this two-stage approach was formally adopted in relation to daylight and sunlight impacts, there would be more opportunity for consistent and balanced decisions to be reached in terms of acceptability.
Stage One deals with the empirical i.e. a calculation of whether a change in daylight and sunlight levels occurs. This can be answered by considering the BRE Guidelines and indeed any other industry recognised methodologies for assessing the impact to and quality of daylight and sunlight.
In essence, Stage One can be broken down into two parts:
- An assessment against the very simplistic and well-known forms of analyses. For daylight, the VSC and NSL analyses and for sunlight, the APSH. A breach of these criteria may mean a noticeable reduction in light and that daylight and sunlight may be adversely affected. However, that initial test would highlight whether a deeper dive into the overall impacts is required.
- Where a noticeable reduction in daylight and/or sunlight occurs, a deeper analysis of impact can be undertaken against the various supplementary assessments provided within the BRE Guidelines, such as retained daylight and sunlight values; room uses; relevant building design limitations e.g. balconies; and, more accurate methodologies such as radiance and climate-based data modelling (CBDM).
All of these factors would contribute to the overall consideration as to whether daylight and sunlight has been adversely affected. The focus would be centered on the daylight and sunlight elements alone and would take reference to the overall guidelines that BRE raise and the wider industry tools for assessment.
Both elements form part of Stage One to establish whether daylight and sunlight been adversely affected.
The question of acceptability (assuming an adverse effect has been identified) is the next consideration.
The most relevant areas of Stage Two, from GIA’s experience at public inquiry, relate to:
- The quality of retained light.
- The number and type of impacted rooms and spaces.
- The expectation of light levels in the given location.
- The development plan, site allocations and wider policy considerations.
- Relevant precedents and strategic guidance both historic and current.
- The strategic importance of the proposal and the benefits it brings.
While this is not an exhaustive list, it is likely that most of the relevant wider contextual considerations would fall into these categories.
It is the availability of all the data under the two stages that should allow both officers and wider decision-makers the opportunity to provide a balanced and conscious view around whether a proposal is appropriate and therefore acceptable.
This approach has been the subject of significant debate at GIA’s most recent public inquiries. On several occasions it has been found that the acceptability of daylight and sunlight impacts cannot be determined by considering Stage One alone. Only by considering Stage One and Two can a balanced judgement be made on whether the impact of a scheme is acceptable. This then fits into the overall planning balance exercise and involves a wider number of issues within the realm of planning judgement.
A formal adoption of the two-stage approach by policy makers would ensure a deeper analysis of impact and context at various stages in the development process. Perhaps, as importantly, it will lead to a more consistent approach to considering the impacts to daylight and sunlight, particularly in urban areas where amenity is only one element of the many planning and development considerations.
To discuss the Two Stage Approach in more detail, contact: