A separate grease duct system shall be provided for each Type I hood. A separate grease duct system is not required where all of the following conditions are met:
1. All interconnected hoods are located within the same story.
2. All interconnected hoods are located within the same room or in adjoining rooms.
3. Interconnecting ducts do not penetrate assemblies required to be fire-resistance rated.
4. The grease duct system does not serve solid fuel-fired appliances.