3D Design Bureau

An Expert Guide To Daylight and Sunlight Assessments

What is a daylight and sunlight assessment?

A daylight and sunlight assessment is a technical analysis that is an integral part of many planning applications. The main purpose of daylight & sunlight assessments is to evaluate the potential impact that a proposed development may have on its surrounding properties and environment. Assessments also evaluate the performance of the proposed scheme itself by testing internal daylight and sunlight of habitable rooms and testing external sunlight in proposed open spaces.

Important Note: It is imperative that daylight and sunlight reports include all information pertaining to the assessment. If full information is not presented and a scheme is granted permission, then the application can run the risk of a Judicial Review due to a positive decision being made without having the full set of information to hand.

Free Daylight & Sunlight Presentation

Daylight and Sunlight Assessments are categorised into two categories: ‘Impact Assessment’ and ‘Scheme Performance’ of which there are several different metrics to assess:

Impact Assessment:

  • Effect on daylight, Vertical Sky Component (VSC), to surrounding properties
  • Effect on sunlight, Annual & Winter Probable Sunlight Hours (A/WPSH) to surrounding properties.
  • Effect on sunlight to surrounding gardens and/or public open spaces, Sun on Ground (SOG)

Scheme Performance:

  • Daylight access, Spatial Daylight Autonomy (SDA) within all habitable rooms of a proposed development.
  • Sunlight access and Sunlight Exposure (SE) for the same rooms tested for daylight access.
  • Sunlight access, Sun On Ground (SOG) to determine the level of sunlight on March 21st in the proposed amenity spaces.
  • Shadow Diagrams. Hourly graphical representation of the shadows cast by a proposed development on the Summer and Winter Solstice (June 21st and December 21st) and Spring Equinox (March 21st). It is very important to note that these images are considered qualitative assessments in support of the quantitative daylight and sunlight assessment. They should not be used as a stand-alone response to any request for assessment of daylight and sunlight.

Due to changes in the 3rd edition of the BRE Guidelines (BRE 209), in June 2022, and the publication of the new Dublin City Council development plan 2022-2028, supplementary ‘Scheme Performance’ studies should also be carried out. These include:

  • An SDA assessment under the I.S. EN 17037 criterion,
  • A No Sky Line (NSL) study within proposed habitable rooms. (This is currently only a requirement for schemes within Dublin City Council due to the publication of the DCC Development Plan 2022 in December 2022)

Most planning authorities now expect daylight and sunlight assessments to be included as standard in planning applications, in particular where it is suspected they may pose a negative effect on the current levels of daylight and sunlight access of neighbouring properties. It is to be noted that the BRE Guidelines state that the guidelines should be treated as ‘guidelines’ and should not be seen as an instrument for planning policies:

“The advice given here is not mandatory and the guide should not be seen as an instrument of planning policy; its aim is to help rather than constrain the designer. Although it gives numerical guidelines, these should be interpreted flexibly since natural lighting is only one of many factors in site layout design.”

That said, all planning authorities, at local and government level, do consider daylight and sunlight assessments, under the BRE Guidelines, as extremely important. They look for proposed property developments to reach a high level of compliance with regard to ‘Impact Assessments’ and ‘Scheme Performance’ and expect a detailed and comprehensive assessment to be carried out under the relevant guidelines and standards.

But understanding and implementing the different guidelines and standards over the past number of years has proven very challenging. Whilst the primary guiding document used for daylight and sunlight assessments is the BRE Guidelines, there are other documents and standards to take into consideration and to include in assessments and reports. For a more in depth review of which guidelines and standards to follow, visit Expert Insights on the Latest BRE Daylight & Sunlight Assessment Guidelines

Why should a daylight and sunlight assessment be carried out?

Daylight and sunlight assessments can be required on all types of property developments, from house extensions and one-off builds to large-scale residential and commercial developments. If there is a possibility that a proposed development may have an impact on the level of daylight and sunlight currently received by neighboring properties, gardens, and open spaces, then a thorough ‘Impact Assessment’ should be carried out. If there are concerns over the design and layout of a proposed scheme, in terms of building positioning, external façade design, and/or internal layouts, then a full ‘Scheme Performance’ assessment should be produced. In most cases, both types of daylight and sunlight assessments, Impact and Scheme Performance, are carried out and included in reports.

It is highly advisable to engage with a suitably qualified and experienced daylight and sunlight consultant as early as possible in the design process. For example, 3DDB have worked on many projects from an early feasibility stage of a project producing high-level façade analysis for VSC (daylight access) on the massing of a proposed design. This helps inform and guide design teams of potential daylight and sunlight issues before a detailed design takes place.

How can you improve daylight and sunlight assessment results?

There are a number of design changes/ideas that can be considered in order to improve daylight and sunlight assessment results for both ‘Impact Assessment’ and ‘Scheme Performance’. Whilst each project is somewhat bespoke, and there are many contributing factors to the results generated on a project, the following list is a good guide to help with underperforming schemes.

  • Improve separation distances of proposed schemes to neighboring properties
  • Amend the heights of proposed buildings along the boundaries to neighboring properties.
  • Consider proposed building layouts and separation distances between blocks on the subject site to ensure that they are not overly obstructing one another from access to daylight and sunlight. This is also very important when considering sunlight in proposed open spaces.
  • Review balcony design and configuration. Consider staggered balconies to reduce obstruction to daylight and sunlight in units below.
  • Avoid recessed balconies with flanking walls that obstruct light.
  • Attempt to reduce depths of internal room layouts. Place storage at the back of rooms for example.
  • Maximise window sizes where possible (width and height) but make sure to consider potential heat gains. This is important and a balance needs to be struck between daylight and sunlight access and heat gains within rooms.

It is important to note that it is the sum of changes that can help improve the compliance rates of a scheme but that there are many other design and planning considerations to take into account. Daylight and Sunlight is one, albeit very important, report in a planning application. Also, where units within a scheme are not achieving the recommended levels of daylight and sunlight, compensatory design measures should be provided.

If you need advice on your project with regard to daylight and sunlight, get in touch with our team who will be more than happy to shed more light on your project! For more information on daylight and sunlight assessments, you can also visit the articles below or book a free presentation with the team by contacting us at info@3ddesignbureau.com or +353 1 2880186.

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