Permeable surfaces promote stormwater infiltration through one of two methods: either through voids in the material itself or voids surrounding the material. Impermeable surfaces increase the stormwater runoff rate and quantity potentially causing pollution and erosion of local watersheds.

Permeable pavements are engineered asphalt or concrete surfaces designed to let stormwater pass through voids in the material itself. This is accomplished by removing small aggregate from the paving material during the manufacture process.

In contrast, permeable pavers are effective due to an open grid that is created in between a network of interlocking paving materials. Bricks are a common example of permeable pavers. Stormwater infiltration occurs due to the voids in between the brick rather than the brick itself. Permeable paver systems are available which contain larger voids (see Figure 1). Vegetation, typically grass, is grown in the voids. Gravel beds are often placed underneath permeable pavers and pavements to increase infiltration capacity.

Figure 1. Installation process for permeable pavement

Figure 2. Landscape plan for the Environmental Protection Agency courtyard in Washington D.C. showing ‘Water Collecting Permeable Concrete’

It is difficult to obtain accurate site costs and life-cycle costs for Permeable Pavements, for so many factors need to be taken into consideration. Please refer to parametric cost estimating tools for the most recent cost estimates. In general, permeable pavement is substantially higher in cost than conventional paving methods; however, stormwater management systems can be reduced balancing the overall construction cost while reducing environmental impact. In addition, some pervious surfaces have a significantly lower life cycle cost due to superior durability, strength, and long life span.

Figure 3. Water permeable concrete completed according to design in Figure 2

Implementation of permeable surfaces is a potential method to achieve the intent of LEED SS Credit 6.1 and SS Credit 6.2. Refer to the LEED Guidance section for specific requirements