Section 504.1/Duct Construction and Installation
UMC 504 covers duct construction requirements including materials, sealing, support, and insulation for HVAC ductwork.
Ductwork must be constructed of materials suitable for the intended service conditions (temperature, pressure, corrosion). Metal duct gauges must comply with SMACNA standards. All duct joints, seams, and connections must be sealed to limit air leakage. Ducts must be supported at intervals per the manufacturer's instructions or the SMACNA duct construction standards. Duct insulation must be provided on supply and return ducts in unconditioned spaces per the energy code requirements.
Why this section exists
Leaky, undersupported, or uninsulated ductwork wastes energy, reduces system capacity, and can create indoor air quality problems. Duct leakage in unconditioned spaces (attics, crawl spaces) means conditioned air is lost before reaching the occupied space. Poorly supported ducts sag over time, restricting airflow and creating noise. Uninsulated ducts in unconditioned spaces gain or lose heat, increasing energy consumption.
What plan reviewers look for
Plan reviewers check duct construction details for material gauge, sealing class, and support methods. They verify duct insulation R-values on the mechanical details, particularly for ducts in unconditioned spaces. They check that flexible duct lengths do not exceed the maximum (typically 5 feet per connection in the UMC) and that rigid duct is used for the main distribution.
Common violations
Related UMC requirements
Section 303 covers combustion air duct requirements. Section 601 covers air distribution system design. IMC Section 603 covers duct construction in the International Mechanical Code. SMACNA HVAC Duct Construction Standards provide the construction details referenced by the code.