Where a common multistory duct system is designed and installed to convey exhaust from multiple domestic kitchen exhaust systems in a building equipped throughout with an automatic sprinkler system in accordance with the Chicago Building Code, the construction of the system shall be in accordance with all of the following:
1. The shaft in which the duct is installed shall be constructed and fire-resistance rated as required by the Chicago Building Code.
2. Dampers shall be prohibited in the exhaust duct, except as specified in Section 18-28-505.3. Penetrations of the shaft and ductwork shall be protected in accordance with Section 717.5.3 of the Chicago Building Code, Exception 1.1.
3. Rigid metal ductwork shall be installed within the shaft to convey the exhaust. The ductwork shall be constructed of sheet metal having a minimum thickness of 0.0187 inch (0.4712 mm) (No. 26 gage) and in accordance with SMACNA Duct Construction Standards.
4. The ductwork within the shaft shall be designed without offsets.
5. The exhaust fan motor design shall be in accordance with Section 18-28-503.2.
6. The exhaust fan motor shall be located outside of the airstream.
7. The exhaust fan shall run continuously and shall be connected to a standby power source.
8. Exhaust fan operation shall be monitored and shall initiate an audible or visible signal at a constantly attended location or at each connection point when the fan is not in operation.
9. Makeup air shall be provided for the exhaust system.
10. A cleanout opening shall be located at the base of the shaft to provide access to the duct to allow for cleaning and inspection. The finished opening shall be not less than 12 inches by 12 inches (305 mm by 305 mm).
11. Screens shall not be installed at the termination.
12. The common multistory duct system shall serve only domestic kitchen exhaust and shall be independent of other exhaust systems.
(Amend Coun. J. 9-14-21, p. 35949, Art. V, § 12)