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TECHNICAL

What’s the optimum rooflight area? NARM, The National Association of Rooflight Manufacturers, has played an important role representing the UK’s rooflight industry in consultation with the Government and its subcontractors, CIBSE, AECOM and the BRE, on issues relating to Part L of The Building Regulations. The following article by NARM’s Technical Committee, explains how small differences in rooflight area can have a significant impact on light levels and energy usage. It is now well understood that correctly specified rooflights save energy and reduce CO2 emissions, making them a critical contributor to meeting Part L of The Building Regulations covering the Conservation of Fuel & Power and the equivalent regional regulations. Independent research by the De Montfort University’s Institute of Energy and Sustainable Development has shown that minimal losses in thermal insulation are greatly offset by energy savings resulting from reduced demand for electric lighting and that generally speaking, the greater the rooflight area the greater the potential savings. However, there is a limit before overheating may become an issue, so an optimum area needs to be identified. There is never a specific solution in respect of rooflight area – judgement is required on a project by project basis. However, the example shown overleaf, demonstrates how data can be interpreted to inform a decision. NARM can supply data for different building locations, for rooflights with varying degrees of light transmission and for different daily time windows. The first consideration in establishing rooflight area, is the use of the

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building. As a typical example, in retail and manufacturing areas, the recommended light level* is 500 Lux. Establishing the appropriate rooflight area to achieve the desired light level is the next point to consider. The larger the rooflight area, the more hours each year the required light level will be provided by natural light. This is the crucial factor affecting energy and emissions reductions – as during these hours, the need for electric lighting is removed.

Mar/Apr 2017

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DAYLIGHTING Magazine issue 3 March/April 2017  Daylighting magazine mar apr 2017:2  

The bi-monthly magazine for architectural specifiers and technicians, building contractors and anyone interested in the provision of natural...

DAYLIGHTING Magazine issue 3 March/April 2017  Daylighting magazine mar apr 2017:2  

The bi-monthly magazine for architectural specifiers and technicians, building contractors and anyone interested in the provision of natural...

Profile for bb2b