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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.
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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.
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Paver Spacing
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.
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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)
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