All joints, longitudinal and transverse seams and connections shall be constructed as specified in SMACNA HVAC Duct Construction Standards – Metal and Flexible and securely fastened and sealed with welds, gaskets, mastics (adhesives), mastic-plus-embedded-fabric systems, liquid sealants or tapes. Tapes and mastics used to seal metallic and flexible air ducts and flexible air connectors shall be listed and labeled in accordance with UL 181B and shall be marked "181 B-FX" for pressure-sensitive tape or "181 B-M" for mastic. Duct connections to sheet metal fittings or flanges of air distribution system equipment and appliances shall be sealed and mechanically fastened. Metallic fasteners for use with flexible nonmetallic air ducts shall comply with UL 181B and shall be marked "181 B-C". Closure systems used to seal all ductwork shall be installed in accordance with the manufacturer's instructions.
Exception: For ducts having a static pressure classification of less than 2 inches of water column (500 Pa), additional closure systems shall not be required for continuously welded joints and seams and locking-type joints and seams. This exception shall not apply to snap-lock and button-lock type joints and seams located outside of conditioned spaces.
(Amend Coun. J. 9-14-21, p. 35949, Art. VI, § 5)