Using rooflighting for heating

Rooflighting can reduce a building’s carbon footprint by minimising heating costs in the colder months – as long as the rooflight area is calculated in such a way to avoid overheating.

• Installing rooflights can generate solar gain (heat from the sun), which is usually a benefit in that it reduces heating requirements and associated carbon dioxide emissions.
• Assuming there are no other significant sources of internal heat, rooflight area of 15% of the floor area will always result in reduction in energy usage for heating.
• In instances where there are other significant sources of internal heat (such as facility processes, artificial lighting and occupants), rooflighting will need to be reduced so that total heating gains do not exceed 35 watts per square metre.

In the Southern Hemisphere, the best way to make use of solar gain (the heating effect of the sun) is to design the building so that windows and rooflights mostly point towards the north, while at the same time minimising the number of those that face the cooler south.

When the building also has solid walls and floors (thermal mass), which have an insulating effect, it will act as a heat store, collecting heat during the day and releasing it as the temperature drops in the evening. The result: radical reductions in the building’s total energy consumption and associated carbon-dioxide emissions.

In buildings used primarily during daylight hours...

• Energy savings is significant in all cases where rooflights constitute 15% of floor area.
• In areas with higher illumination, these benefits are significantly improved by increasing the rooflight area to 20%.
• In areas with low illumination, there is no benefit to increasing the rooflight area beyond 15%.

• Energy savings is significant in all cases where rooflights constitute 15% of total floor area.
• In areas with high illumination, there are minor additional savings to be had by increasing rooflight area to 20%.
• In areas with low illumination, most of the energy savings occur where rooflighting constitutes up to 10% of the floor area. Increasing this to 15% results in minor further savings. However, increasing rooflight area even more, to 20%, actually results in a slight increase in carbon dioxide emissions.

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