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October 3, 2016 <br /> Single-Family Residence <br /> • L&A Job No. 16-124 <br /> Page 19 <br /> Building Footing Drains <br /> A subdrain should be installed around the perimeter footings of the proposed residence <br /> and the uphill side of concrete retaining walls or interior foundation walls. The subdrain <br /> should consist of a 4-inch-minimum-diameter, perforated, rigid, drain pipe, wrapped in a <br /> non-woven filter fabric (Mirafi 14ONS) laid at bottom of drain line trenches. The <br /> trenches should be at least 10 inches wide and 12 inches below bottom of footings of the <br /> building or retaining walls. 'Me trenches and drain lines should have a sufficient gradient <br /> (0.5% minimum) to generate flow by gravity. The drain tines should be wrapped in a <br /> non-woven filter fabric sock and completely enclosed in clean washed gravel. The <br /> remaining trenches may be backfilled with clean onsite soils. Water collected by the <br /> perimeter footing subdrain system should be tightlined, separately from the roof and <br /> surface stormwater drain lines, to discharge into a storm sewer or suitable stormwater <br /> disposal facilities. Clay or lean concrete dams should be constructed in the tightline <br /> trenches at the upper end of the tightlines to prevent water in the drain line trenches to <br /> flow through. <br /> Surface Drainage <br /> Water should not be allowed to stand in areas where footings, on-grade slabs, or <br /> pavement is to be constructed. Finish ground surface should be graded to direct surface <br /> runoff away from the residence building. We recommend that finish ground be sloped at <br /> a gradient of 3 percent minimum for a distance of at least 10 feet away from the building, <br /> except in areas to be paved. <br /> LIU & ASSOCIATES, INC. <br /> 24 <br />