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should be stable. When the height of the wall reaches three times the depth of the SRW unit, it is prudent to include geogrid rein- forcement to stabilize the wall and the retained soil. The inclusion of geogrids allows SRWs to be built to greater heights. Determining the type, length and elevation of the geogrid lay- ers required to construct a stable wall typically requires engineer- ing skills. However, a conservative preliminary design can be used for initial costing of a project. At a later stage in the design phase, an engineer can review the initial design and adjust the plan as needed. A conservative initial design may incorporate geogrid, placed in continuous layers every 12 to 24 inches vertically with a length equal to the height of the wall and not less than 4 feet long. This conservative design would only be usable for typical in- stallations: backfilled with compacted, dense-graded aggregate, pedestrian-only loading behind the wall with no slope, con- structed on a stable undisturbed subgrade to a maximum total height of 6 feet. Project layout and site preparation Site preparation typically includes identifying site access and staging areas; permits and approved drawings; identifying slopes and drainage; installing erosion control and containment measures; and providing protection for trees, plantings and structures. Project layout is more than just spray painting a line on the contractor and are approved by the homeowner. Therefore, the time and expense should be part of the contractor's price. Depending on the building codes for the project, and the measured vertical difference in elevation between patio areas, it may be necessary to install railings or other types of guards. In some areas, the building codes only require retaining walls over 48 inches tall (measured from the leveling pad to top of wall) to be designed and draw- ings stamped by a licensed engineer. Other areas have implemented regu- lations that require full engineering for retaining walls with heights as low as 24 inches. Generally, seg- mental retaining walls built to a height equal to or less than twice the depth of the seg- mental retaining wall (SRW) unit grass to indicate the patio border. The location of all utilities and buried lines should be verified and marked by the utility location company. The main task in job layout is transferring the final de- sign from a sheet of paper to the job site. This is done by establish- ing a convenient elevation benchmark; marking the extent of the excavation and patio; noting important features such as corners, curves and steps; installing offset stakes and string lines; and mark- ing the finished elevation with stakes and marks on adjacent struc- tures. The last step in the project layout is obtaining the owner's approval in writing. Material management A typical job requires a lot of material that needs to be received on site and temporarily stored until it is needed. Most of the time the local municipality will not allow materials to be stored on the street. Planning material deliveries, storage, and backyard access become critical components to the success of the job. Ensure that delivery trucks comply with local code require- ments, and that stockpiled material is out of the way of the owner, the neighbors and construction activities. Most projects should have materials delivered as needed. If all material was delivered at the beginning of the project, the site would be overcrowded, and productivity would drop. Make provisions for the equipment stor- age and vehicle parking. Maintaining a clean, organized site makes a favorable impression for a company and helps earn future busi- ness. Geogrid reinforcement can be used to stabilize segmental retaining walls and allow them to built to greater heights. www.landscapeirrigation.com Waterproofing When building a raised patio, water and moisture control needs to be addressed at the beginning of the project. Typically, a mini- mum grade of 1.5 percent is ideal to ensure that water flows across the surface. If the slope is lower than this, the water won't move off of the patio. For larger patio areas, surface drains may be con- structed. For smaller patios, water may flow across the patio, over Landscape and Irrigation 15