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I I INTERIOR ENVIRONMENT tirI in direct contact with the underside of the structuralat the perimeter of each individual sheet interior roof sheathing. 5.1.2. Where air-permeable insulation is surface to form a continuous layer. Exceptions: provided inside the building thermal 1. Section 1203.3 does not apply to special use stmc- envelope, it shall be installed in tares or enclosures such as swimming pool enclo- accordance with Item 5.1. In addi- sores, data processing centers, hospitals or art tion to the air-permeable insulation galleries. installed directly below the struc- tural sheathing, rigid board or sheet 2. Section 1203.3 does not apply to enclosures in Cli_ ' insulation shall be installed directly mate Zones 5 through 8 that are humidified beyond • • above the structural roof sheathing 35 percent during the three coldest months. in accordance with the R values in 1203.4 Under-floor ventilation. The space between the bot- Table 1203.3 for condensation con- torn of the floor joists and the earth under any building except trol. spaces occupied by basements or cellars shall be provided with ventilation openings through foundation walls or exte- 5.1.3. Where both air-impermeable and rior walls. Such openings shall beplaced so as to provide I air-permeable insulation are pro- sided, the air-impermeable insula- cross ventilation of the under-floor space- tion shall be applied in direct contact 1203.4.1 Openings for under-floor ventilation. The net with the underside of the structural area of ventilation openings shall be not less than 1 square roof sheathing in accordance with foot for each 150 square feet(0.67 m2 for each 100 m1)of Item 5.1.1 and shall be in actor- crawl-space area. Ventilation openings shall be covered dance with the R values in Table for their height and width with any of the following mate- ," 1203.3 for condensation control. rials, provided that the least dimension of the covering The air-permeable insulation shall shall be not greater than I/a inch(6.4 mm): �; be installed directly under the air- 1. Perforated sheet metal plates not less than 0.070 impermeable insulation. inch(1.8 mat)thick. 5.1.4.• Alternatively, sufficient rigid board 2. Expanded sheet metal plates not less than 0.047 inch or sheet insulation shall be installed (1.2 mm)thick directly above the structural roof sheathing to maintain the monthly 3. Cast-iron grilles or gratings. average temperature of the under- 4. Extruded load-bearing vents. E. side of the structural roof sheathing above 45°F (7°C). For calculation 5. Hardware cloth of 0.035-inch (0.89 mm) wire or • t purposes, an interior air temperature heavier. of 68°F (20°C) is assumed and the 6. Corrosion-resistant wire mesh,with the least dimen- exterior air temperature is assumed sion not greater than'/s inch(3.2 rum). to be the monthly average outside air 1203.4.2 Exceptions. The following are exceptions to • temperature of the three coldest Sections 1203.4 and 1203.4.1: • months. • 1. Where warranted by climatic conditions,ventilation 5.2.Where preformed insulation board is used as the openings to the outdoors are not required if ventila- air-permeable insulation layer,it shall be sealed Lion openings to the interior are provided. • • I TABLE 1203.3 INSULATION FOR CONDENSATION CONTROL CLIMATE ZONE MINIMUM R-VALUE OF AIR-IMPERMEABLE INSULATION' 28 and 3B tile roof only 0(none required) I,2A,28,3A,3B,3C R-5 4C R-10 4A,48 R-15 ' 5 R-20 6 R-25 7 R-30 = 411/ $ R-35 a. Contributes to, but does not supersede, thermal resistance requirements for attic and roof assemblies in Section C40221 of the International Energy Conservation Code. 312 2015 INTERNATIONAL BUILDING CODE" 1