NARM’s technical committee discusses
Optimum rooflight areas

The National Association of Rooflight Manufacturers (NARM) continues to fly the flag for the UK’s rooflight industry in terms of issues relating to Part L of the Building Regulations and its technical committee has recently penned an article on how minor changes to the size of rooflight areas can have a major impact on internal light levels and subsequent energy usage.

The committee revealed that correctly specified and installed rooflights do save energy and minimise CO2 emissions, playing a contributory role in buildings meeting Part L relating to the Conservation of Fuel and Power.

Furthermore, research undertaken by De Montfort University’s Institute of Energy and Sustainable Development has revealed that the use of rooflights and the subsequent minimal losses in thermal insulation are offset hugely by energy savings as a consequence of a reduced need for electric-powered lighting.

Nevertheless, the committee insists that it’s not as easy as saying ‘the greater the rooflight area, the greater the potential savings’. In fact, there is a limit before it becomes an issue of overheating, with the need for an optimum rooflight area to be identified.

The committee first discusses the use of a rooflight in a building when establishing an optimum rooflight area. It states the need to find the appropriate rooflight area that achieves the desired light levels of the building in question. The larger the rooflight area, the more annual hours of natural light will be provided.

The graph demonstrated here relates to a single storey building in the London area, between the hours of 6am-6pm ad with rooflights generating 50% transmission of natural light. The graph clearly shows that as the rooflight area increases, the length of time a given illumination level is achieved, is extended.

Consequently, a building requiring 500 Lux light levels e.g. in retail and manufacturing premises, the graph shows that 10% rooflight areas will achieve 500 Lux for almost half (46%) of the working year. If that rooflight area rises to 15%, it’s possible to achieve 500 Lux for almost three-fifths (58%) of the working year. In these terms, a building with 10% rooflight areas will need electric lights to be switched on for approximately 30% hours more per year than premises with 15% rooflight areas.

NARM concludes by insisting it is possible for correctly specified rooflights to generate excellent long-term returns on investment, whilst enhancing the building’s own sustainability credentials. As proud NARM members, at Sunsquare we’re pleased to see the association work hard to raise awareness and reinforce the importance of designing with natural daylight in mind.