Raised patios of segmental retaining walls (SRWs) and interlocking concrete pavers (ICPs) are rapidly gaining popularity. This combination provides a beautiful, cost competitive, and virtually maintenance-free patio. The installation methods are similar to separate installations of these products.

Installation begins with the SRW. This should be built on firm, well-compacted soil graded at least at a 1% slope downward and away from the house. It sits on a compacted, crushed aggregate foundation. The foundation should be no less than 24 inches (600 mm) wide and 6 inches (150 mm) deep. For exact depth, most SRW suppliers provide guidelines.

To provide extra strength, at least one-tenth of the wall height should be buried below grade. This, along with suitable drainage behind the wall, prevents the SRW from sliding, rotating, or tilting.

For proper drainage, a 6-inch-diameter (150 mm) perforated drain pipe should be installed along the back face of the first course of the wall. The pipe lies on the bottom of a coarsely graded aggregate drainage layer. The largest size of the aggregate should be ¾ inch (75 mm) of free-draining angular material with no fines. It should extend a minimum of 12 inches (300 mm) behind the wall and extend the full height less the dense-graded, compacted base thickness that supports the bedding sand and pavers. At least one end of the pipe should extend to daylight.

Well-compacted crushed stone base is used as fill behind the drainage layer. Since this will be the paver base, it must be carefully compacted in a maximum of 6-inch (150 mm) lifts. It should be separated from the drainage layer with geotextile to prevent fines from infiltrating the larger aggregate. Geotextile should be placed horizontally to separate the compacted soil subgrade from the compacted aggregate base above, which supports bedding sand and concrete pavers.

Geogrid can provide extra stability for the SRW. Geogrid is typically connected between the wall units and extends into the compacted base backfill. Generally, it is laid on the bottom course. In tall walls, another layer is placed every 2 feet (600 mm) vertically. SRW manufacturers can provide guidance for proper vertical spacing and installation.

The bedding sand and pavers are installed according to Interlocking Concrete Pavers Institute (ICPI) guidelines. The surface of each base layer should be smooth with the slope already established in the compacted soil subgrade under the SRW foundation. String lines help maintain accurate and consistent slopes for each layer. The top base layer should be brought just below the top of the SRW so the pavers sit flush with the top of the SRW units. The slope in the wall should enable the base and pavers to drain water away from the building.

For more information on pavers and SRWs, visit www.icpi.org and www.ncma.org.

— Daniel Kokonowski and Pieter VanderWerf work for Building Works, Inc. (www.buildingworks.com), a consulting firm that helps companies introduce new construction products. Source material for the article provided by Dave Smith at ICPI.