Most Professional Home Builders in Portland have heard of Permeable Interlocking Concrete Pavers. Only a small percentage of builders have actually installed permeable pavers in streets or residential driveways. Their reason for hesitancy in using permeable pavers likely revolves around fear of the unknown—things like engineering, installation, cost and maintenance. The aim of this article is to give a general overview of each of these topics. Let’s first take a look at installation steps used in permeable paver street, cul-de-sac and driveway construction.

Jobsite conditions:

1. Assess soil conditions. Clay soils will accept rainwater at a slower rate than sand or gravel soil. Most rainfall events will drain into the subgrade within 24 to 36 hours. In jobsite conditions where the percolation rate of the subgrade soil is less than 1/2 inches per hour, drain tiles are usually placed in the lowest aggregate layer to carry away excess water.
2. Decide how many inches of a 24-hour rainfall you want to capture, store and allow to seep into the subgrade. The desired rainwater storage goal will be one of the factors that determine the depth of the lower base aggregate layer. For example, a 10 inch base layer of aggregate has 40% void space will store approximately 4 inches of rainwater.
3. Determine if the rainfall runoff from adjacent property or roofs will drain on to the permeable pavers. If the answer is yes, the depth of the base aggregate needs to be increased to accommodate the water volume.
4. Determine the vehicular traffic loads that the pavement will need to handle. This is another factor that affects the depth of the lower base aggregate layer. Permeable paver pavements accept heavy loads by design. As weight is applied to the paver surface it is transferred horizontally to adjacent pavers and it is transferred down in a spreading footprint to the subgrade soil.
5. Know the seasonal high water table. If the water table is closer than 3 feet from the surface, special design considerations come into play.

Installation:
After the pavement design is completed, the following construction steps are commonly used

1. Excavate the pavement area. Do not compact the subgrade; doing so will reduce the percolation rate of the soil.
2. Install concrete edge restraint around the perimeter of the planned pavement.
3. Place geotexile on the subgrade, if required (determined by strength of subgrade soil).
4. Install large size crushed base rock and compact in 4 to 8-inch lifts using 10- ton rolling compactor.
5. Install and compact a 4-inch layer of medium size crushed aggregate.
6. Screed a 2-inch layer of small crushed bedding layer aggregate. Do not compact.
7. Set permeable pavers on bedding aggregate.
8. Fill joints between pavers with small crushed aggregate.
9. Compact the paver surface with an 8500 lb. force plate compactor.
10. Top-off the joint aggregate level, filling to lower beveled edge of paver units.
11. Remove excess small aggregate.
12. Permeable pavers can be installed in all weather conditions. The pavement is ready for use immediate after installation.

Residential driveway:
Driveway design and installation varies slightly from street installation since they are not usually subjected to heavy vehicular loads, so the large size base rock layer can be eliminated from the design. The depth of the medium size aggregate layer is increased to accommodate light vehicular loads, commonly 7 to 10 inches. In driveway installations, plastic edge restraint is sometimes preferred; it becomes invisible after turf or bark dust is installed around the driveway edge.

Cost:
The cost of permeable paver pavement is comparable to other pavements, in some cases less expensive than impermeable pavements when long term durability and the elimination of traditional underground storm systems and detention ponds are factored in. Jobsite conditions influence permeable paver pavement costs.

Streets:
Generally speaking, streets will have a material (aggregate & pavers) and labor cost of $5.50 to $6.50 per square foot. The pavers will be installed using specializes machines. Engineering, excavation and concrete curbing are not included is this cost estimate.

Residential driveways:
Residential driveways are installed by hand-setting the pavers; the cost is approximately $9 to $15. Residential project costs vary greatly because jobsite conditions vary greatly.

Maintenance:
Maintenance of permeable paver streets and parking lots is much the same as that of traditional impermeable pavements. Vacuum sweeping is recommended to be done a minimum of two times a year using standard equipment. Snow & ice maintenance costs are significantly less on permeable paver pavements. 

Residential permeable paver driveways require little maintenance. Grass clippings and leaves should be kept off the paver pavement to deter clogging and weed growth.

For more information contact:
Gale Schroeder
Willamette Graystone
Web: www.willamettegraystone.com
Email: gales@willamettegraystone.com
Phone: (971) 241-0312