Daylight and Sunlight Assessments for Developers 2018-03-19T08:55:05+00:00

Daylight & Sunlight Matters for Developers

Daylight & Sunlight Assessments for Planning Applications

Many Local Authorities often request that a developer submits a Daylight and Sunlight Assessment to accompany a Planning Application, many now even before they will even validate the application.

This will normally follow standard industry used criteria as laid down in the document known as “Site Layout Planning for Daylight and Sunlight – A Guide to Good Practice, 2nd Edition’, by Paul Littlefair. This was formerly titled “BRE Digest 209”, and is commonly still referred to as this.

There are two types of assessment a property developer may be asked for:

1A ‘Within’ Assessment

This is an assessment to see whether your new development (usually residential in nature, for example, new housing, flats or student accommodation) will be able to enjoy good daylight and sunlight following completion. Thus, it seeks to assess your own scheme, and has consideration of things such as room layouts, window glazing, and internal reflectance values of wall, floor and ceiling finishes.

If you can demonstrate through a Daylight and Sunlight Assessment that your new development will enjoy good conditions, then this is more likely to contribute positively to the approval of the scheme.

If however the new design cannot demonstrate a good level of daylight and sunlight to the Local Authority, they can ask you to adapt your scheme so as to improve such conditions. This can lead to a delay in getting your scheme validated, as any amended design will normally have to be re-assessed to demonstrate an improvement to the planning officer.

Failure to address such matters can result in a scheme being refused planning permission.

2A ‘Neighbouring’ Assessment

If your new development is situated close to other nearby properties, the Local Authority might be concerned that your scheme may have an adverse impact upon the daylight and sunlight currently enjoyed by such properties. This is especially so if the neighbouring buildings are residential in nature.

You may be asked to assess this risk, sometimes even before your application will be validated.

This type of report seeks to assess the amount of daylight the neighbours’ windows are capable of achieving, and, if a neighbours’ room layout is known, it may also seek to demonstrate how the daylight is distributed within the neighbours’ room. The tests also seek to assess how much sunlight the neighbours’ windows will get over the course of the year, and, how much sunlight they will get in winter months.

The other aspect sometimes considered here is the impact that the new development may have upon overshadowing to the neighbour’s principal outdoor amenity and garden areas.

Often one of these reports can assist with a planning application if it can demonstrate low impact upon neighbouring properties. Indeed, sometimes, because of demolition of existing site structures, improvements to conditions serving neighbouring properties can be demonstrated.

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“Dear Adrian, Thought you might like to see the appeal decision received this afternoon. After all this time it is great news. Your report has undoubtedly helped in the final decision, so thank you very much from Jane and me for all your excellent work.”

“Smith Marston Ltd helped us gain planning approval on our two storey extension after a number of objections from neighbours. The advice they gave and the detailed letter to the council gave factual information to dismiss unfounded objections.”

Technical Information on Daylight & Sunlight Matters

Demonstration that a scheme satisfies the guidance contained with the BRE guide for daylight and sunlight can be very useful to the progress of a development scheme through the planning system.

We have been involved with numerous schemes where concerns have been raised by the planning officer and/or neighbours regarding daylight and sunlight to neighbouring existing buildings potentially affected by the proposed development. Often though we are able to demonstrate that the scheme satisfies the guidance described within the BRE document and thus remove this obstacle to the progression towards planning permission.

On some occasions, the BRE Daylight and Sunlight assessments are commissioned proactively by the developer to support a scheme whilst on other occasions this may be something requested by the planning department. It is worth noting that a planning application submitted without a Daylight and Sunlight assessment, but where one would be appropriate, may be delayed through the planning process if such a study is then requested by the planning department after submission of the planning application.

In addition to BRE assessments in relation to the effect of the development upon the neighbouring buildings and external amenity areas, ‘Within Development’ assessments can also be requested by Local Authorities to demonstrate that the development building itself will receive adequate natural daylight and sunlight.

This considers only the hours of sunlight a window will receive over a 12 month period. Because the test relates only to sunlight, only windows facing within 90 degrees of due south are considered under the methodology contained with the BRE document Site Layout Planning for Daylight & Sunlight.

The guidance is that main windows should receive at least 25% of the ‘total probable sunlight hours’ for a 12 month period. This should include 5% of the total probable sunlight hours over the winter months between 21 September and 21 March.

This takes no account of direct sunlight and assesses only the amount of diffuse light within a room related to an affected window.

The principal method of assessing this is a measure of the amount of sky visible from the window of an affected room. This assessment component is called the Vertical Sky Component (VSC). For a window of a room to be adversely affected under the BRE guidance, the window must have a view of less than 27% of the ‘dome of the sky’ (a VSC of less than 27%) and the VSC must be less than 0.8 times its previous value.

A further more detailed assessment is called the Average Daylight Factor. This is a measure of the actual likely natural diffuse daylight in a room taking account of various matters influencing this such as the reflectivity of surfaces and the glazing in the window. The no sky-line is a measure of those parts of the room which have no view at all of the sky at all.
The BRE guidance suggests that consideration of sunlight to external areas should normally include:

  • Gardens, usually the main back garden of a house, and allotments;
  • Parks and playing fields;
  • Children’s playgrounds;
  • Outdoor swimming pools and paddling pools;
  • Sitting-out areas, such as those between non-domestic buildings and in public spaces;
  • Focal points for views, such as a group of monuments or fountains.

The BRE guide recommends that at least half of the garden/amenity area should receive at least two hours of direct sunlight on 21 March.

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