Overview
A daylight sunlight assessment is a technical report which is often commissioned as part of the planning process to check that reasonable levels of daylight will provided either within or around a proposed new development. As part of the development management process, planning authorities will often ask that the promoters of a specific development submit a daylight assessment that has been prepared in accordance with the methods detailed in the BRE Guide 'Site layout planning for daylight and sunlight' 2022, otherwise known as BR209. In this article, we introduce the key differences between daylight, sunlight, and skylight and we present the two primary types of Daylight Sunlight Assessments that can be commissioned for planning purposes. First, let's start with the main terminology.
What is the difference between daylight, sunlight, and skylight?
The terms Daylight, Sunlight and Skylight are familiar terms that can often be used interchangeably in normal discourse; however, they have very specific meanings within the field of planning.
What does sunlight refer to in planning assessments?
Sunlight refers to the solar radiation (within the visible spectrum) which travels directly from the sun in parallel rays.
What does skylight refer to in planning assessments?
Skylight refers to the solar radiation (within the visible spectrum) which reaches the earth having first been scattered in the earth’s atmosphere.
What does daylight refer to in planning assessments?
Daylight refers to the natural light that is available during the day (from sunrise to sunset) and includes both sunlight and skylight. A Daylight Sunlight Assessment which has been carried out in accordance with the recommendations of the BRE Guide 'Site layout planning for daylight and sunlight' 2022 will typically contain several component assessments that consider each of these facets of natural light separately. Further to this, a Daylight Sunlight Assessment can take two different forms depending on what is being considered. The two forms of daylight sunlight assessments which are often prepared for planning submissions include a Daylight Performance Assessment and a Daylight Impact Assessment.
What is a daylight performance assessment?
This type of daylight sunlight assessment considers the adequacy of natural light which will be provided within a proposed development. The natural light provided within the proposed interior spaces and outdoor recreation spaces is typically considered and testing is conducted in accordance with the technical recommendations detailed in the BRE Guide 'Site layout planning for daylight and sunlight' 2022. GV8 has prepared an in-depth guide to Daylight Performance Assessment at the following link. A detailed guide to preparing a Daylight Performance Assessment.
What is a daylight impact assessment?
This type of daylight sunlight assessment differs from a daylight performance assessment because it focuses on the light levels that will exist in the neighbourhood of a proposed development. A daylight impact assessment considers the loss of light that would register on neighbouring properties as a consequence of a proposed development and sets out to determine if this loss falls within reasonable bounds. Daylight impact testing is generally carried out in accordance with the test methodologies detailed in the BRE Guide 'Site layout planning for daylight and sunlight' 2022. GV8 has prepared an in-depth guide to Daylight Performance Assessment at the following link. A detailed guide to preparing a Daylight Impact Assessment.
Who prepares a daylight sunlight assessment?
Daylight sunlight assessments are typically prepared by a daylight consultant. This is a growing field of practice in Ireland and the UK which will at some stage in the future be supported by a formal training pathway and represented by a dedicated professional body. In the meantime, you will find that daylight consultants typically have backgrounds in either engineering, surveying, architecture or architectural visualization. As a loosely regulated profession, it is important for clients exercise diligence when choosing a daylight consultant to work with. While the technical methods required to run daylight testing are clearly prescribed, the guidance available does not cover all situations, and it will often be the case that important decisions, about how an assessment should be conducted and reported, need to be made in reliance on the daylight consultants past experience and professional judgement.
How much does a daylight sunlight assessment cost?
This is a difficult question to answer as so many factors influence the assessment's duration. As a general guide, the following factors have a significant bearing on time and costs.
Factors that will tend to increase the cost of a daylight sunlight assessment
- When running a daylight impact assessment, the number of neighbouring properties that could be affected by the proposed development. This not only effects the number of buildings and windows that need to be modelled but greatly increase the amount of background research which needs to be carried out to determine the types of rooms that would be affected and their sensitivity to impact.
- When running a daylight performance assessment, the number of rooms within the proposed development is the primary factor influencing time and cost.
- In some cases, where it seems likely that a proposed development is going to comfortably satisfy daylight standards, it can be possible to carry out a single pass assessment of a proposed development after the design has been fully resolved. Where multistage assessment is required this will tend to increase the cost of testing.
- The scope of testing will play a role in time and costs. This not only relates to the percentage of rooms and windows that are tested but also the number of component tests which are run. For cost saving purposes not all of the tests recommended in the BRE Guide 'Site layout planning for daylight and sunlight' 2022 have in the past typically been run in Ireland and the UK. When commissioning a daylight assessment clients will have to decide whether they are happy to run with a traditional scope of assessment or, in the interest or minimising planning or judicial risk, they would prefer to run a more complete suite of studies. Where a more complete suite of studies are commissioned this will inevitably increase time and costs.
Factors that will tend to decrease the cost of a daylight sunlight assessment
Separate to the above, some additional factor which can help reduce the cost of a daylight assessment are detailed below.
- For daylight impact assessments the availability of a good topographical survey of the immediate neighbourhood will help reduce the time required to build a 3D representation of the neighbouring context.
- For daylight performance assessments the time required to run testing can be reduced if a fully developed 3D model of the proposed development can be provided.
