Porous Asphalt
About Porous Asphalt
General Information Performance Data Water Quality Treatment Process Design

The use of porous asphalt pavement could drastically reduce the need for road salt in winter conditions. Since the application of salt can be problematic for small receiving streams and is not treated by most stormwater systems, such source reduction is crucial.

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About Porous Asphalt

Porous asphalt systems are an extremely effective approach to stormwater management. Unlike retention ponds, they do not require large amounts of additional space. Instead, rainfall drains through pavement and directly infiltrates the subsurface. This significantly reduces runoff volume, decreases its temperature, improves water quality, and essentially eliminates impervious surface. It also speeds snow and ice melt, dramatically reducing the salt required for winter maintenance. The porous asphalt design tested at UNHSC is distinctive in its use of coarse sand for a reservoir base and filter course—a refinement that enhances its effectiveness in treating water quality.

Where to Use It

The effectiveness of porous asphalt has been demonstrated over a wide range of climates, including those with winter freezing. It may be especially effective in cold climates given its durability and capacity to reduce the salt needed for deicing in winter conditions.

As with most LID stormwater practices, porous asphalt is suitable for many sites. Typically, it is recommended for parking lots and low use roadways, and is ideal for proposed developments with large areas of impervious surface. As with any infiltration system, care must be taken when locating these systems near pollution hotspots, or where seasonal high groundwater levels may lead to groundwater contamination. In such cases, the system can be lined and outfitted with a subdrain that discharges to the surface.


Improvements in mix design, requirements for infiltration, and the need to comply with the Clean Water Act Phase II have combined to make porous asphalt a reasonable stormwater management alternative. Clogging, poor mix specifications, structural failure, and other historical barriers to implementation have been addressed. Successful implementation of these systems relies on proper mix production, construction, and installation— all of which can be achieved with qualified suppliers and engineering oversight.

The materials and installation cost of UNHSC’s porous asphalt lot was approximately $2,300 per parking space; the adjacent impervious asphalt lot was $2,000 per space. The net cost for both lots would be comparable if the impervious lot’s stormwater infrastructure were taken into consideration. This porous lot has proven durable year round, and has not been maintained to demonstrate a worse case scenario. Design specifications are online: www.unh.edu/erg/cstev