On the other hand, all supply & return ducts located in an unconditioned space or outdoors shall have all joints sealed to SMACNA Class A seal level in accordance with the SMACNA “HVAC Duct Construction Standards – Metal & Flexible”. Class A seal level requires that transverse seams, longitudinal and all applicable penetrations be sealed (mastics, liquids, or gaskets).
For more information on the new requirements, please visit the Building Code website and click on Division B Part 6.