When paving materials incorporate small gaps, water can seep through into quick-draining gravel layers below that then gradually sink into the soil. This eliminates runoff and keeps the top surface dry.
There are three basic types: concrete pavers with voids in between to be filled with gravel or sand (with or without grass); porous concrete or asphalt made with little or no sand so there are built-in air pockets; and plastic grids that keep a surface layer of gravel or sand (with or without grass) from compacting, so water drains through.
Materials and Installation
Pervious paving is suitable for gentle inclines that slope no more than 1 foot over a horizontal distance of 20 feet. Though a small-scale paver or grid-system project like a pervious walkway or patio might be a DIY job, you'll likely need professional design help for a driveway, where soil is heavy with clay or freezes deeply, or if the job is tied into a building permit. Pervious concrete and asphalt (which cost 20 percent more than their conventional counterparts) always require professional installation.
Plastic-grid systems are the most DIY-friendly, requiring a gravel base layer of only 2 to 6 inches, compared with about a foot for the other systems. The base can be tamped with a plate compactor, which you can rent; the material is simply rolled out and pinned down along the edges; and spaces are filled with decorative gravel or sand, plus grass seed, if you like.
As more communities limit the amount of impervious surfaces (rooftops, conventional hardscape) allowed on residential lots, interest in pervious paving has skyrocketed. "It can literally be a trade-off between installing a pervious driveway and adding a room," says designer Jan Johnsen. "Or a question of whether you can build that new patio at all." In those cases, pervious paving is not only an attractive way to deal with runoff, it's a double-duty enhancement, one that lets you keep on improving your home while you safeguard its natural environment.
Shown: Some concrete pavers have larger spaces to hold sand and turf grass, which absorb some storm water near the surface.
Anatomy of a Quick-Draining Driveway
A: Concrete pavers with spaces in between for gravel
B: Border paver (optional)
C: Edge restraint
D: 1½ inches of 1/8- to 3/8-inch crushed gravel
E: 4 inches of ½- to 1-½-inch crushed stone extending 6 inches past drive to handle overflow
F:: 4 to 5 inches of 2- to 3-inch crushed stone, as needed
G: Geotextile (optional)