Section 5.1.1/Air Duct Construction
NFPA 90A Section 5.1 covers duct construction materials, fire dampers at rated penetrations, and duct sealing requirements.
Air ducts must be constructed of approved materials with adequate thickness to maintain structural integrity and resist fire. Metallic ducts (galvanized steel, aluminum) must comply with SMACNA standards for gauge thickness based on duct dimensions and pressure class. Non-metallic ducts (fiberglass ductboard, flexible duct) must be listed and labeled for the intended application. Ducts penetrating fire-resistance-rated assemblies must be protected by fire dampers or must be enclosed in a rated shaft. All duct joints and seams must be sealed to limit air leakage per the applicable sealing class.
Why this section exists
HVAC ducts connect every occupied space in a building. Without proper construction and fire protection, a duct system becomes a highway for fire and smoke to spread from one fire compartment to another in minutes. A duct that burns through during a fire adds fuel and creates openings in rated assemblies. Fire dampers at rated penetrations and smoke dampers at smoke barrier penetrations are critical to maintaining compartmentation during a fire.
What plan reviewers look for
Plan reviewers check the duct material specification against NFPA 90A and SMACNA requirements. They verify fire dampers at every duct penetration through a fire-resistance-rated wall, floor, or ceiling assembly. They check for smoke dampers at smoke barrier penetrations. They verify that flexible duct is listed for the application and does not exceed the maximum length.