Establishing the optimum rooflight area with NARM

31 Jan 2018

NARM, The National Association of Rooflight Manufacturers, have been explaining how minor differences in rooflight area can make a substantial impact on light levels and energy usage, courtesy of its Technical Committee.

With it being common knowledge that specified rooflights save energy and lower CO2 emissions, this also makes them a vital component to meeting Part L of The Building Regulations covering the Conservation of Fuel & Power and the equivalent regional regulations.

Research has shown minimal losses in thermal insulation are massively offset by energy savings, leading to a lessened demand for electric lighting and, generally speaking, the larger the rooflight area, the more savings could be potentially made. There is, however, a limit before overheating could manifest as an issue, so an optimum area has to be identified.

A specific solution never exists in terms of rooflight area, with judgement essential based on whatever the project may be. However, the example (click here to see) shows how data gathered can be used to inform a decision. NARM can provide data for varying 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 building; for 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 next; the larger the rooflight area, the increased amount of hours every year the necessary light level will be natural light. This is a vital factor affecting energy and emissions reductions, as there is no need for electric lighting during these hours.

The graph in the link shows a single storey building in London, between 6am and 6pm daily, with rooflights providing 50% light transmission. It shows, as the rooflight area across the bottom of the graph increases, the length of time a given illumination level is achieved, is extended.

So a building which requires 500 Lux, the yellow line shows with 10% rooflights, 500 lux would be achieved for approximately 2000 hours (46% of the working year).

For further information, please contact NARM using the contact details on our website, where you will be directed to the appropriate person.

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