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47.5 MB - The Whole Building Design Guide

47.5 MB - The Whole Building Design Guide

47.5 MB - The Whole Building Design Guide

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For interior non-load-bearing masonry walls in critical facilities locatedwhere the basic wind speed is greater than 120 mph, see therecommendations given in Section 3.3.3.3.3.4.3.4 Roof Systems<strong>The</strong> following types of roof systems are recommended for criticalfacilities in hurricane-prone regions, because they are more likelyto avoid water infiltration if the roof is hit by wind-borne debris,and also because these systems are less likely to become sources ofwind-borne debris:m In tropical climates where insulation is not needed above theroof deck, specify either liquid-applied membrane over cast-inplaceconcrete deck, or modified bitumen membrane torcheddirectly to primed cast-in-place concrete deck.m Install a secondary membrane over a concrete deck (ifanother type of deck is specified, a cover board may beneeded over the deck). Seal the secondary membrane atperimeters and penetrations. Specify rigid insulation overthe secondary membrane. Where the basic wind speed isup to 110 mph, a minimum 2-inch thick layer of insulationis recommended. Where the speed is between 110 and 130mph, a total minimum thickness of 3 inches is recommended(installed in two layers). Where the speed is greater than 130mph, a total minimum thickness of 4 inches is recommended(installed in two layers). A layer of 5 / 8-inch thick glass matgypsum roof board is recommended over the insulation,followed by a modified bitumen membrane. A modifiedbitumen membrane is recommended for the primarymembrane because of its somewhat enhanced resistance topuncture by small missiles compared with other types of roofmembranes.<strong>The</strong> purpose of the insulation and gypsum roof board is toabsorb missile energy. If the primary membrane is puncturedor blown off during a storm, the secondary membrane shouldprovide watertight protection unless the roof is hit withmissiles of very high momentum that penetrate the insulationand secondary membrane. Figure 3-86 illustrates the merit ofMAKING CRITICAL FACILITIES SAFE FROM High Wind3-107

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