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Roof surface & area



It is critical to ensure that your roof surface is suitable for collecting good quality rainwater. In fact this is the first check in the “How to create the complete Rain Harvesting System” – a practical guide we have developed to help you design and plan a complete rain harvesting system.

For more information about the importance of roof material selection click here

Just as important as the roofing material used, is the need to ensure gutters are installed to the appropriate standards, that gutter protection systems be considered in particularly leafy or fire prone areas, and that gutter outlets be installed on the undersides of roof gutters to prevent sludge build up. More information is available as part of our “12 Steps” guide.


roof shot 2



Because of their sheer size, roofs will catch a significant amount of water. The roof catchment area for single storey homes is usually greater than the floor area of the building if there are eaves.

As a guide to collection capacity, consider that each 1mm of rain = 1 Litre (L) of water per square metre (m2) of roof area, then allow a 15% wastage factor.

Another rule of thumb is that the smaller the catchment area the larger the tankbecause when it rains there is a need to capture as much as possible of the run-off.