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47.5 MB - The Whole Building Design Guide

47.5 MB - The Whole Building Design Guide

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3.4.4.2 Mechanical PenthousesBy placing equipment in mechanical penthouses rather thanleaving them exposed on the roof, equipment can be shieldedfrom high-wind loads and wind-borne debris. Although screens(such as shown in Figure 3-77) could be designed and constructedto protect equipment from horizontally-flying debris, they are noteffective in protecting equipment from missiles that have an angulartrajectory. It is therefore recommended that mechanicalequipment be placed inside mechanical penthouses. <strong>The</strong> penthouseitself should be designed and constructed in accordancewith the recommendations given in Sections 3.4.2 and 3.4.3.3.4.4.3 Lightning Protection Systems (LPS)Lightning protection systems frequently become disconnectedfrom rooftops during hurricanes. Displaced LPS components canpuncture and tear roof coverings, thus allowing water to leak intobuildings (see Figures 3-94 and 3-95). Prolonged and repeatedslashing of the roof membrane by loose conductors (“cables”) andpuncturing by air terminals (“lightning rods”) can result in liftingand peeling of the membrane. Also, when displaced, the LPS is nolonger capable of providing lightning protection in the vicinity ofthe displaced conductors and air terminals.Figure 3-94:A displaced air terminalthat punctured themembrane in severallocations. HurricaneMarilyn (U.S. VirginIslands, 1995)MAKING CRITICAL FACILITIES SAFE FROM High Wind3-115

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