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ENGEO <br /> INCORPORATED <br /> <br /> <br />5150.100.101 <br />May 2, 2008 Page 17 <br />3. Discharge roof down spouts into closed conduits and direct away from buildings to <br />appropriate drainage devices. <br /> <br />6.8.2 Subsurface Drainage <br /> <br />Because of the anticipated perched groundwater in the proposed cuts, we recommend designing a <br />subdrain system below the floor to remove any seepage that goes below the adjacent wall drain <br />and surfaces under the building. We recommend that, as a minimum, the following measures be <br />incorporated in the floor and wall design: <br /> <br />1. A subdrain should be constructed around the perimeter of the building. The subdrain pipe <br />should be lower in elevation than the interior floor grade. It is preferred to design the <br />subdrain to drain by gravity to an appropriate discharge location rather than use some type <br />of sump pump that is subject to power supply failure and maintenance concerns. <br /> <br />2. The floor slab should be designed with an underslab subdrain system. <br /> <br />3. The building walls that act as retaining structures should be designed with a waterproofing <br />system and all construction joints should incorporate some type of water stop. <br /> <br />4. A waterproofing expert should be consulted for more specific recommendations as the <br />client feels is necessary. <br /> <br />Construct subdrains as follows: <br /> <br />1. Excavate an 8-inch-wide trench to a minimum depth of 3 feet below (finish grade, existing <br />grade, finish subgrade). <br /> <br />2. Slope the entire trench bottom at a minimum of 1 percent. <br /> <br />3. Lay enough filter fabric equivalent (Mirafi 140NC or equivalent) in the trench to completely <br />encapsulate the aggregate subdrain following completion, including a minimum overlap of <br />12 inches. <br />