Page 86 - 2018_IMC

CHAPTER 6

DUCT SYSTEMS

User note:
About this chapter: Chapter 6 addresses duct systems used in HVAC systems and some exhaust systems. Some exhaust system ducts are
addressed in Chapter 5, such as kitchen exhaust ducts and clothes dryer exhaust ducts. This chapter addresses air plenums such as above-ceil-
®
ing and below-floor plenums. Section 607 covers fire and smoke dampers, consistent with the requirements of the International Building Code .

SECTION 601 4. The air-handling system serving the corridor is shut
GENERAL down upon detection of sprinkler waterflow where
the building is equipped throughout with an auto-
601.1 Scope. Duct systems used for the movement of air in
air-conditioning, heating, ventilating and exhaust systems matic sprinkler system.
shall conform to the provisions of this chapter except as oth- 5. The space between the corridor ceiling and the floor
erwise specified in Chapters 5 and 7. or roof structure above the corridor is used as a com-
ponent of an approved engineered smoke control
Exception: Ducts discharging combustible material
directly into any combustion chamber shall conform to the system.
requirements of NFPA 82. [BE] 601.3 Exits. Equipment and ductwork for exit enclosure
ventilation shall comply with one of the following items:
[BE] 601.2 Air movement in egress elements. Corridors
shall not serve as supply, return, exhaust, relief or ventilation 1. Such equipment and ductwork shall be located exterior
air ducts. to the building and shall be directly connected to the
Exceptions: exit enclosure by ductwork enclosed in construction as
required by the International Building Code for shafts.
1. Use of a corridor as a source of makeup air for 2. Where such equipment and ductwork is located within
exhaust systems in rooms that open directly onto the exit enclosure, the intake air shall be taken directly
such corridors, including toilet rooms, bathrooms, from the outdoors and the exhaust air shall be dis-
dressing rooms, smoking lounges and janitor clos- charged directly to the outdoors, or such air shall be
ets, shall be permitted, provided that each such cor- conveyed through ducts enclosed in construction as
ridor is directly supplied with outdoor air at a rate required by the International Building Code for shafts.
greater than the rate of makeup air taken from the
corridor. 3. Where located within the building, such equipment and
ductwork shall be separated from the remainder of the
2. Where located within a dwelling unit, the use of cor-
ridors for conveying return air shall not be prohib- building, including other mechanical equipment, with
construction as required by the International Building
ited.
Code for shafts.
3. Where located within tenant spaces of 1,000 square In each case, openings into fire-resistance-rated construc-
2
feet (93 m ) or less in area, use of corridors for con- tion shall be limited to those needed for maintenance and
veying return air is permitted.
operation and shall be protected by self-closing fire-resis-
4. Incidental air movement from pressurized rooms tance-rated devices in accordance with the International
within health care facilities, provided that the corri- Building Code for enclosure wall opening protectives. Exit
dor is not the primary source of supply or return to enclosure ventilation systems shall be independent of other
the room. building ventilation systems.
[BE] 601.2.1 Corridor ceiling. Use of the space between 601.4 Contamination prevention. Exhaust ducts under posi-
the corridor ceiling and the floor or roof structure above as tive pressure, chimneys and vents shall not extend into or
a return air plenum is permitted for one or more of the fol- pass through ducts or plenums.
lowing conditions: Exceptions:
1. The corridor is not required to be of fire-resistance- 1. Exhaust systems located in ceiling return air ple-
rated construction.
nums over spaces that are permitted to have 10 per-
2. The corridor is separated from the plenum by fire- cent recirculation in accordance with Section
resistance-rated construction. 403.2.1, Item 4. The exhaust duct joints, seams and
3. The air-handling system serving the corridor is shut connections shall comply with Section 603.9.
down upon activation of the air-handling unit smoke 2. This section shall not apply to chimneys and vents
detectors required by this code. that pass through plenums where such venting sys-

2018 INTERNATIONAL MECHANICAL CODE  69
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