Permeable paving is designed to reduce the volume of surface run-off, particularly in urban areas, and hence lower the risk of flooding. By allowing rainwater to infiltrate into the ground across a wide area, rather than forcing it into a few specific locations, this type of paving mimics natural drainage systems. It is often specified for car parks as part of a sustainable urban drainage system (SUDS).
Permeable paving flags are available in various finishes, including granite aggregate, aged, tumbled and textured, to match the aesthetics of the broader scheme. Some can also be machine laid. Typically manufactured to BS EN 1338. The permeability of an installation, which is dependent on the laying pattern, is measured in litres per second per hectare.