Enclosed attics and enclosed rafter spaces formed where ceilings are applied directly to the underside of roof rafters shall have cross ventilation for each separate space by ventilation openings. The ventilation openings shall be tested for rain and snow infiltration in a manner representative of the intended installation and shall not permit the entrance of rain and snow when so tested. Ventilation openings shall not be provided in roof areas, or portions thereof, which are subject to snow drift as determined by Section 13-52-280.
The minimum required net free ventilating area shall be 1/150 of the area of the space ventilated. Where ridge or gable vents are utilized, one- half of the ventilation openings shall be provided by ridge or gable vents, with the balance of the ventilation openings provided by eave or cornice vents. The openings shall be covered with corrosion-resistant mesh or other approved materials with openings not more than 1/2 inch (13 mm) in any direction.
The minimum required area is permitted to be reduced to 1/300, provided that a vapor retarder having a permeance not exceeding 1 perm is installed on the warm side of the ceiling; or the ridge or gable ventilation openings are located in the upper third of the space to be ventilated with the balance of the required ventilation provided by eave or cornice vents.
Crawl space areas, other than those used as an underfloor plenum, shall be ventilated by an approved mechanical means or by openings in exterior foundation walls. Openings shall be located as close to corners as practicable and shall provide cross ventilation on at least two approximately opposite sides. The openings shall be covered with corrosion-resistant mesh not less than 1/4 inch (6 mm) nor more than 1/2 inch (13 mm) in any direction.
Openings shall have a net area of not less than 1 square foot (0.093 m2) for each 150 square feet (13.95 m2) of foundation space. Where an approved vapor retarder is installed over the ground surface, the required net area of openings shall be reduced to 0.1 square foot (0.093 m2) for each 150 square feet (13.95 m2) and vents shall have manually operable louvers.
Alternative mechanical ventilation. Enclosed attic, rafter and crawl spaces which are not ventilated as herein required shall be equipped with a mechanical ventilation system conforming to the requirements of the mechanical code listed in Chapter 13-176*, Chapter 13-180*, Chapter 13-184* and Chapter 13-192*.
(Added Coun. J. 4-29-98, p. 66679, § 1)
* Editor’s note – Coun. J. 7-9-03, p. 3609, § 1, repealed Ch. 13-176, which pertained to ventilation, Ch. 13-180, which pertained to heating provisions, Ch. 13-184, which pertained to warm air heating plants, and Ch. 13-192, which pertained to mechanical refrigeration.