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total vent area shall be in the lower half of the ventilated <br />space. <br />402.1.1.6 Radiant Barrier. A radiant barrier shall have an emissivity of <br />no greater than 0.05 as tested in accordance with ASTM E -408. The <br />radiant barrier shall be installed with the shiny side facing down and with <br />a minimum air gap thickness of 3 /4 -inch below. The radiant barrier may be <br />securely attached to the roof framing or may be laminated to the bottom of <br />the roof sheathing. <br />402.1.1.7 Cool Roof. A cool roof shall have an infrared emittance of no <br />less than 0.75 when tested in accordance with ASTM E -408 and a high <br />solar reflectance. The manufacturer's test results shall be acceptable for <br />compliance. <br />402.1.1.8 Roof Heat Gain Factor. The Roof Heat Gain Factor (RHGF) <br />shall not exceed 0.05 when calculated as described in Equation 402.1.1 -1. <br />Equation 402.1.1 -1 <br />RHGF = U,x a x RB <br />Where: <br />RHGF = Roof Heat Gain Factor (Btu/ft -h - ° F) <br />Ur = overall thermal transmittance value for the gross area of <br />opaque roof surfaces (Btu/ft -h - ° F) <br />a = roof surface absorptivity. Between 0.3 and 1.0 (unitless) <br />RB = Radiant Barrier credit. Equals 0.33 if a radiant barrier is <br />installed and 1.00 otherwise (unitless). Radiant barrier installation <br />must comply with Section 402.1.1.8.1 to qualify for Radiant <br />Barrier credit. <br />402.1.1.8.1 Radiant Barrier Credit. To quality for the radiant barrier <br />credit (RB) described in Section 402.1.1.8, the installation of the radiant <br />barrier must meet the following criteria: <br />1. The emissivity of the radiant barrier must be 0.10 or less. <br />The manufacturer must provide test data or documentation <br />of the emissivity as tested in accordance with ASTM E- <br />408. <br />2. The radiant barrier must be securely installed in a <br />permanent manner using one of the following installation <br />methods: <br />2.1 The radiant barrier shall be draped with the shiny <br />side facing down over the top cord of the truss <br />before the roof deck is installed. A minimum air gap <br />of 3 /4 -inch must be provided between the radiant <br />barrier and the roof deck above at the center of the <br />2 <br />