Chapter 6, Section 602.4, is hereby deleted in its entirety and the following provision shall be substituted therefor:

Joints and Seams of Ducts. Joints of duct systems shall be made substantially airtight by means of tapes, mastics, gasketing, or other means. Crimp joints for round ducts shall have a contact lap of at least 1-1/2" and shall be mechanically fastened by means of at least three (3) Sheet-metal screws equally spaced around the joint, or an equivalent fastening method.

Exception: Residential ducts and joints in conditioned spaces, as long as the joints for round ducts, in conditioned spaces, have a contact lap at least 1 1/2" and shall be mechanically fastened by means of at least three (3) Sheet-metal screws equally spaced around the joint, or equivalent fastening method, the joint is substantially airtight.