Daylight Calculations for Planning

What is Daylight Planning?

Daylight Studies are carried out in order to determine the potential for natural light to enter a room. The efficient utilisation of daylight in a property will reduce its dependence on artificial lighting, thereby enhancing its energy performance and environmental credentials.

There are different types of daylighting studies we can help with, each responsible for assessing separate factors of daylight upon new and existing buildings. These include:

• Overshadowing Assessments also known as Vertical Sky Component
• Annual Probable Sunlight hours
• Internal Daylight Assessments also known as Average Daylight Factor

Why do you need Daylight Studies?

It is common now for local authorities to ask for daylighting issues to be addressed as part of planning applications for any impact on your proposed development. All buildings will be required to have adequate levels of daylight and this should be a priority for new developments. Where possible, and in line with other policies and guidelines, new developments should be built to take advantage of daylight to provide a pleasant living environment.

These studies can also identify any potential infringements to neighbouring properties. So, for instance, if the level of daylight they experience is affected to a noticeable extent by a development, it could be used an objection to a planning application and may even result in potential financial compensations further down the line.

How can we help?

At Base Energy, all our Daylight Studies are carried out in accordance with BRE 209 Standards, the highest industry benchmark, and are accepted by all local planning authorities.

Our team has a proven track record of success in this area. You will receive a comprehensive evaluation report conducted by a leading specialist and we can offer you the most competitive prices on the market.

For more information on Daylight Studies, or to speak with one of our specialist assessors, please call us on 020 3286 2016 or email us at info@baseenergy.co.uk and we will get back to you within the same working day.

More on the services we provide….

Overshadowing Assessments

With the sheer volume of intercity building taking place at the moment, the need to assess a development’s impact on the availability of daylight to surrounding properties has never been more imperative.

Although there is no existing National Planning Policy relating to this at present, the BRE Report ‘Site Layout Planning for Daylight and Sunlight: A Guide to Good Practice’ acts as the established national guidance on this.

It has been developed in conjunction with daylight and sunlight recommendations in the National Building Specification’s BS 8206: Part 2: ‘Lighting for Buildings – Code of Practice for Daylighting’ .

Base Energy conducts all its assessments in line with this policy. The most common method for calculating the change in daylight to existing buildings, as recommended in BRE Digest 2009, is the ‘Vertical Sky Component (VSC)’.

The VSC method measures the general amount of light available on the outside plane of the window as a ratio (%) of the amount of total unobstructed sky viewable following introduction on visible barriers such as buildings.

The relevant BRE recommendations for daylight, when using the VSC method measured at the centre of a window, should be no less than 80% of its former value.

Sunlight Assessments

The same method used for the VSC test is applied to calculate Annual Probable Sunlight Hours (APSH) which is also expressed as a percentage.

The BRE Guidelines also notes ‘Access to sunlight should be checked for the main window of each room which faces within 90 degrees of due south’.

Therefore, any windows facing 90 degrees due north does not need to be analysed as there is no expectation of sunlight. APSH can also be used to assess the effects of external amenity space such as gardens, playgrounds etc. The relevant BRE recommendations for sunlight are a follows:

“The window should receive at least 25% of available annual sunlight hours and more than 5% during the winter months ( September 21st to March 21st), and 80% of its former value”

Average Daylight Factor for Internal Daylight Assessments

The preferred method of assessment for the internal daylight of a room, as provided by BRE Guidelines, is the ‘Average Daylight Factor Method.’(ADF).

The ADF is defined as ‘A ratio of total daylight flux incident on a reference area to the total area of the reference area, expressed as a percentage of outdoor luminance on a horizontal plane, due to an unobstructed sky of assumed or known luminance distribution’.

The ADF method takes into account:

• The diffusible visible transmittance of the glazing to the room in question (how much light gets through the window glass)
• The net glazed area of all the windows in the room
• The total area of the room surfaces (floor, walls, ceiling and windows)
• The angle of visible sky reaching the window/windows in question

The recommended ADF value is dependent upon the use of the room in question. The BRE Guidelines suggest % ADF value for each of the following rooms:

• Kitchens – 2%
• Living Room – 1.5%
• Bedrooms – 1%

If the given room meets its relevant criteria, then it will be regarded as having adequate daylight.