Increased rooflight area saves energy!
Rooflights make a positive contribution to the internal environment in a building, but also reduce energy use and cost, and contribute to the external environment by reducing the carbon footprint, helping to meet the requirements of Part L Building Regulations.

And the greater the rooflight area, the bigger the contribution the rooflights can make.

Rooflight area should be between 15% and 20% of the roof
Research demonstrates that installing between 15%-20%
rooflights can greatly reduce a buildings CO₂ emissions.

Installing from between 15% to 20% of the roof area in rooflights is a practical solution to ensure the lighting levels within the building are adequate and, together with automatic control of electric lighting, delivers considerable reduction in a building?s energy requirement, and hence reduces CO₂ emissions.

The notional building used in Part L Building Regulations assumes 20% roof area in rooflights and research demonstrates that installing less than this amount will make compliance more

Independent research
The De Montfort University?s Institute of Energy and Sustainable Development is a leading authority on energy use and it has undertaken considerable research into the effect rooflights have on a building's energy consumption. This graph, generated from De Montfort University research, shows how CO₂ emissions vary with rooflight area and with different lighting requirements and occupancy patterns.

In every case adding rooflights provides very significant savings. The size of the saving depends on how much light is required inside the building and how many hours per day the building is occupied. The savings are greatest for buildings needing a bright interior during daytime occupancy.

Rooflights are performance enhancers
Rooflights don?t just improve the external environment, they improve the internal environment too. People prefer natural light, and there is a growing body of scientific evidence to suggest that it helps us perform better. Studies have shown that school children learn better, hospital patients recover quicker, factory workers are more productive and shoppers linger longer, spending more.
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Interior lighting levels
It is important that designers also consider possible future change of use of a building when determining rooflight area, and ensure that daylight levels are sufficient for all likely future uses.

A rooflight area of 15% - 20% will provide adequate natural light for most buildings. Light is measured in lux, the table below
shows the light level required for different activities.

Solar overheating
De Montfort University research shows in a large volume building,
with evenly distributed rooflights and moderate internal heat gains
a rooflight area up to 20% will not cause solar overheating.