Air dispersion systems are not just "fabric duct." IMC 603.17 treats them as a specific product type with specific installation limits. If you are using one, the drawings need to show that it is in the right location, under the right pressure condition, kept out of rated construction, and properly listed.
Plain English:
Must be installed entirely in exposed locations (no above-ceiling or concealed runs).
Positive-pressure systems only - cannot be used in exhaust or negative-pressure applications.
Cannot pass through or penetrate fire-resistant-rated construction.
Must be listed and labeled in compliance with UL 2518.
On Plans: Why it matters
These systems are often selected for aesthetics, cost, or distribution performance in open spaces, but they are easy to misuse on permit sets. Common misses are showing them above ceilings, using them in negative-pressure applications, or routing them through rated walls like standard ductwork. That is where the redlines start.
Code Path: Where to show it
M-001: air dispersion system note with exposed-location, positive-pressure, and UL 2518 basis
M-101: clearly show exposed routing and identify where the system starts and ends
M-501: mounting / termination details and transition to conventional ductwork
Life safety / architectural plans: confirm no rated wall or floor penetrations
M-601: product schedule or note identifying listed air dispersion system
Check: Do
Clearly identify the system as an air dispersion system, not just "fabric duct"
Show that it is fully exposed and under positive pressure
Coordinate transitions before any rated assembly
Review Risk: Don't
Don't route air dispersion systems above ceilings or in concealed spaces
Don't use them in negative-pressure applications
Don't run them through rated walls, floors, or other rated construction
Field Tip:
A simple review check is this: if it is soft duct-like distribution material, ask four questions right away: is it fully exposed, is the system positive pressure, does it avoid rated construction, and is the UL 2518 basis shown? If not, expect a redline.
Masterbuild QA Lens
Duct system pressure class (603.2) determines the construction standard for all fittings, joints, and reinforcement. Confirm the design static pressure is on M-001, that the pressure class is carried through to every duct schedule note, and that the contractor is required to construct to the specified pressure class and test before concealment. A pressure class note that does not match the duct schedule is a document coordination error.
Drawing / Submittal Check
For 603.17 (air dispersion systems): the drawings must show the fabric or perforated duct layout with the hole pattern and the pressure class. Confirm the air dispersion system is listed and the listing covers the application (supply only - not return or exhaust). Show the seam orientation and the connection to the rigid duct upstream. Air dispersion systems submitted without the listing reference are a common first-cycle comment.
Common Review Risk
Air dispersion (fabric or perforated duct) systems with holes that are sized for design conditions but not installed correctly (wrong orientation, partial inflation, or blocked sections) are a common commissioning failure. These systems must be balanced to achieve uniform distribution - confirm the commissioning protocol includes an air distribution test for the full duct length.
When To Escalate
Escalate when the air dispersion system commissioning reveals poor distribution - when some zones receive significantly more or less air than the design calls for. Air dispersion systems that do not distribute uniformly after commissioning may require re-perforation of the duct fabric, which requires the manufacturer's input and possibly a new submittal.
Rated Assembly Coordination
Section 603.17 air dispersion systems using fabric or porous ducts in ceiling spaces may interact with rated ceiling assembly requirements. Confirm the listed product is compatible with the ceiling assembly rating and that any penetrations are properly protected.
Duct System Coordination
Section 603.17 covers air dispersion systems and unconventional supply configurations. If the design uses fabric duct, perforated panels, or underfloor diffusers, confirm the product is listed and the airflow pattern is coordinated with the space layout.