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Phelan Development Holly Master Plan - Buildings H & 1 15188.000.006 Geotechnical Exploration The structural engineer should provide final design thickness and reinforcement, as necessary, for the intended structural loads. 7.1.3 Slab Moisture Vapor Reduction When buildings are constructed with concrete slab-on-grade, water vapor from beneath the slab will migrate through the slab and into the building. This water vapor can be reduced but not stopped. Vapor transmission can negatively affect floor coverings and lead to increased moisture within a building. When water vapor migrating through the slab would be undesirable, such as in any designated office areas where floor coverings may be applied, for example, we recommend installation of a durable vapor retarder beneath the concrete floor. The vapor retarder should be sealed at all seams and pipe penetrations and connected to all footings. Vapor retarders should conform to Class A vapor retarders in accordance with ASTM E 1745-97 "Standard Specification for Plastic Water Vapor Retarders used in Contact with Soil or Granular Fill under Concrete Slabs." The structural engineer should be consulted as to the use of a layer of clean sand or pea gravel (less than 5 percent passing the U.S. Standard No. 200 Sieve)placed on top of the vapor retarder membrane to assist in concrete curing. 7.2 EXTERIOR FLATWORK Exterior flatwork includes items such as concrete sidewalks, steps, and outdoor courtyards exposed to foot traffic only. Provide a minimum section of 4 inches of concrete over 4 inches of AB. Compact the AB to at least 90 percent relative compaction (ASTM D1557). Thicken flatwork edges to at least 8 inches to help control moisture variations in the subgrade and place wire mesh or rebar within the middle third of the slab to help control the width and offset of cracks. Construct control and construction joints in accordance with current Portland Cement Association Guidelines. 7.3 TRENCH BACKFILL Backfill and compact all trenches below building slabs-on-grade and to 5 feet laterally beyond any edge in accordance with Section 5.7.2. 8.0 RETAINING WALLS 8.1 LATERAL SOIL PRESSURES For drained and restrained retaining walls, such as loading dock walls, at-rest lateral earth pressures should be considered. Table 8.1-1 provides lateral earth pressures for retaining wall design with level backfill conditions. TABLE 8.1-1: Lateral Earth Pressures for Drained Retaining Walls with Level Backfill ACTIVE PRESSURE(PCF) AT-REST PRESSURE(PCF) 45 65 In accordance with 2016 California Building Code requirements, foundation walls and retaining walls supporting more than 6 feet of backfill height are to be designed for dynamic seismic lateral earth pressures corresponding to design earthquake ground motions. We recommend a dynamic —NGE0 Page 1 19 December 13, 2021 Expect Exceltence