The recent Building Regulations also, for the first time, recommend a minimum rooflight area for industrial and commercial buildings, recognising the significant benefits of natural light and the effectiveness
of rooflights in allowing daylight into a building.The Regulations recommend a minimum rooflight area of 10% to achieve a 'daylit' classification and a nominal area in heated buildings of 20%. If the rooflights achieve a U value below 2.2W/m²K, a larger rooflight area could be incorporated.The new standards are easily achieved using site assembled double or triple skin rooflights in GRP or polycarbonate, with little or no increased cost or complexity.

0.25 W/m²K

Characteristics ofactivity/interior

*Table based on research by Institute of Energy and Sustainable Development, De Montfort University for illuminance in the horizontal plane - rooflight area should be greater where illumination is needed in the vertical plane eg. where vertical racking is used.

**Figures for the level of illuminance required are taken from CIBSE Guide A (table 1.12).

Whilst the heat loss calculations are based on an area of 20%, the recommended maximum to prevent solar overheating is 12%, unless one of the alternative methods of reducing solar overheating is employed, or it is demonstrated by calculation that solar overheating will not occur.

Recent independent research by Institute of Energy and Sustainable Development at De Montfort University concludes that, in general, the minimum rooflight areas needed to provide adequate illuminance are significantly lower than the maximum limits to avoid solar overheating, dependent on internal gains in the building.Typically rooflight areas of 17% to 20% can accommodate internal gains of 5 to 10W/m²
.