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• <br />UNDERDRAIN SYSTEM <br />Floors constructed below grade should be protected by an underdrain system. The <br />underdrain system should consist of perimeter drains. Free-draining granular material used in <br />the drain system should consist of minus 2-inch aggregate with less than 50% passing the No. <br />4 sieve and less than 3 % passing the No. 200 sieve. <br />Floor slabs above exterior grade do not require under drainage unless moisture-sensitive <br />floor coverings are used, to prevent capillary moisture rise through the slab. Two methods of <br />controlling capillary moisture (vapor) rise are to place the slab directly on free-draining gravel <br />as described above or to use a manufactured moisture barrier such as 20 mil PVC under 3-inches <br />• of clean sand. <br />The drains should consist of drain file or perforated pipe placed in the bottom of a filter <br />cloth lined (AMOCO 4504 or equivalent) trench and surrounded above the invert level with free- <br />draining granular material. The free-draining baclo`"rll should extend up to the slab level. The <br />perimeter drains should be at least 4 inches in diameter. The drain lines should be placed at <br />least 1-foot below the floor level and graded to a sump or sumps at a minimum slope of 1 % <br />where water can be removed by bailing or pumping. <br />SITE DRAINAGE <br />Moisture-sensitive soils were identified on this site. The satisfactory performance of <br />foundations, floor slabs and roads are directly tied to positive surface and subsurface drainage <br />• <br />• 28 <br />