ADOPTS WITH AMENDMENTS:

International Residential Code 2015 (IRC 2015)

Part I — Administrative

Part II — Definitions

Part III — Building Planning and Construction

Part IV — Energy Conservation

Part V — Mechanical

Part VI — Fuel Gas

Part VII — Plumbing

Part VIII — Electrical

Part IX — Referenced Standards

Heads up: There are no amended sections in this chapter.

Chapter 15 Exhaust Systems

AMENDMENT
This section has been amended at the state or city level.
The text of this chapter is extracted from the 2018 edition of the North Carolina Mechanical Code and has been modified where necessary to conform to the scope of application of the North Carolina Residential Code for One- and Two-Family Dwellings. The section numbers appearing in parentheses after each section number are the section numbers of the corresponding text in the North Carolina Mechanical Code.

M1501.1 (501.3) Outdoor Discharge

AMENDMENT
This section has been amended at the state or city level.
The air removed by every mechanical exhaust system shall be discharged to the outdoors in accordance with Section M1506.3. Air shall not be exhausted into an attic, soffit, ridge vent or crawl space. Exhaust shall not be directed onto walkways, balconies, decks, breezeways, covered walkways and similar horizontal projections.

Exceptions:
  1. Whole-house ventilation-type attic fans that discharge into the attic space of dwelling units having private attics shall be permitted.
  2. Where installed in accordance with the manufacturer's instructions and where mechanical or natural ventilation is otherwise provided in accordance with Sections M1507 or R303.1, listed and labeled domestic ductless range hoods shall not be required to discharge to the outdoors.
Clothes dryers shall be exhausted in accordance with the manufacturer's instructions.

M1502.1.1 (504.6) Makeup Air

AMENDMENT
This section has been amended at the state or city level.
Where a closet is designed for the installation of a clothes dryer, an opening having an area of not less than 100 square inches (0.0645 m2) shall be provided in the closet enclosure or makeup air shall be provided by other approved means.

The delayed effective date of this Rule is January 1, 2021.
The Statutory authority for Rule-making is G. S. 143-136; 143-138.
Dryer exhaust systems shall be independent of all other systems and shall convey the moisture to the outdoors.

Exception: This section shall not apply to listed and labeled condensing (ductless) clothes dryers.

M1502.3 (504.8.7) Duct Termination

AMENDMENT
This section has been amended at the state or city level.
Exhaust ducts shall terminate on the outside of the building. Exhaust duct terminations shall be in accordance with the dryer manufacturer's installation instructions. If the manufacturer's instructions do not specify a termination location, the exhaust duct shall terminate not less than 3 feet (914 mm) in any direction from openings into buildings. Exhaust duct terminations shall be equipped with a backdraft damper. Screens shall not be installed at the duct termination or weather cap outlet. An exhaust duct shall terminate not less than 12 inches (305 mm) above finished grade.

Exception: Where the duct termination is less than 12 inches (305 mm) above finished grade, an areaway shall be provided with a cross-sectional area not less than 200 square inches (1290 cm2). The bottom of the duct termination shall be no less than 12 inches (305 mm) above the areaway bottom.

M1502.4 (504.8) Dryer Exhaust Ducts

AMENDMENT
This section has been amended at the state or city level.
Dryer exhaust ducts shall conform to the requirements of Sections M1502.4.1 through M1502.4.7.

M1502.4.1 Material and Size

AMENDMENT
This section has been amended at the state or city level.
Exhaust ducts shall have a smooth interior finish and be constructed of metal having a minimum thickness of 0.0157 inches (0.3950 mm) (No. 28 gage for steel, No. 26 gage for aluminimum). With the exception of the transition duct, flexible ducts are prohibited. The duct shall be 4 inches (102 mm) nominal in diameter.

M1502.4.2 Duct Installation

AMENDMENT
This section has been amended at the state or city level.
Exhaust ducts shall be supported at intervals not to exceed 4 feet (3658 mm) and shall be secured in place. The insert end of the duct shall extend into the adjoining duct or fitting in the direction of airflow. Exhaust duct joints shall be sealed in accordance with Section M1601.4.1 and shall be mechanically fastened. Ducts shall not be joined with screws or similar fasteners that protrude into the inside of the duct. Ducts shall be sealed in accordance with Section M1601.4.1.
  1. Nonmetallic mechanical fasteners (tie-straps) shall be listed to UL 181B.
  2. Metal band duct clamps are not required to be listed.
The delayed effective date of this Rule is January 1, 2021.
The Statutory authority for Rule-making is G. S. 143-136; 143-138.
UpCodes note: Prior to January 1, 2021, the first sentence of this section was  "Exhaust ducts shall be supported at intervals not to exceed 12 feet (3658 mm) and shall be secured in place. ".  There seems to be a typo in the new amendment, please note that 4 feet is equivalent to 1219.2 mm.

M1502.4.3 (504.8.3) Transition Duct

AMENDMENT
This section has been amended at the state or city level.
Transition ducts used to connect the dryer to the exhaust duct system shall be a single length that is listed and labeled in accordance with UL 2158A. Transition ducts shall be not greater than 8 feet (2438 mm) in length. Transition ducts shall not be concealed within construction and must remain entirely within the room where the appliance is located.

M1502.4.4 (504.8.4.3) Dryer Exhaust Duct Power Ventilators

AMENDMENT
This section has been amended at the state or city level.
Domestic dryer exhaust duct power ventilators shall conform to UL 705 for use in dryer exhaust duct systems. The dryer exhaust duct power ventilator shall be installed in accordance with the manufacturer's instructions.

M1502.4.5 (504.8.4) Duct Length

AMENDMENT
This section has been amended at the state or city level.
The maximum allowable exhaust duct length shall be determined by one of the methods specified in Sections M1502.4.5.1 through M1502.4.5.3.
The maximum length of the exhaust duct shall be 35 feet (10 668 mm) from the connection to the transition duct from the dryer to the outlet terminal. Where fittings are used, the maximum length of the exhaust duct shall be reduced in accordance with Table M1502.4.5.1. The maximum length of the exhaust duct does not include the transition duct.

TABLE M1502.4.5.1
DRYER EXHAUST DUCT FITTING EQUIVALENT LENGTH
DRYER EXHAUST DUCT FITTING TYPE EQUIVALENT LENGTH
4 inch radius mitered 45 degree elbow 2 feet 6 inches
4 inch radius mitered 90 degree elbow 5 feet
6 inch radius smooth 45 degree elbow 1 foot
6 inch radius smooth 90 degree elbow 1 foot 9 inches
8 inch radius smooth 45 degree elbow 1 foot
8 inch radius smooth 90 degree elbow 1 foot 7 inches
10 inch radius smooth 45 degree elbow 9 inches
10 inch radius smooth 90 degree elbow 1 foot 6 inches

For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 degree = 0.0175 rad.
The size and maximum length of the exhaust duct shall be determined by the dryer manufacturer's installation instructions. The code official shall be provided with a copy of the installation instructions for the make and model of the dryer at the concealment inspection. In the absence of fitting equivalent length calculations from the clothes dryer manufacturer, Table M1502.4.5.1 shall be used.
The maximum length of the exhaust duct shall be determined in accordance with the manufacturer's instructions for the dryer exhaust duct power ventilator.

M1502.4.6 Length Identification

AMENDMENT
This section has been amended at the state or city level.
Where the exhaust duct equivalent length exceeds 35 feet (10 668 mm), the equivalent length of the exhaust duct shall be identified on a permanent label or tag. The label or tag shall be located within 6 feet (1829 mm) of the exhaust duct connection.
  1. Labels shall be permanently stenciled, laminated, or commercially available plastic or metal tags.
  2. Labels shall state, at a minimum (fill in the blank):

    Caution: Equivalent length _____ ft. Any installed dryer must be equipped with an exhaust system that meets or exceeds this equivalent length requirement.
  3. Labels can be attached to wall or vent receptor.

M1502.4.7 (504.8.5) Exhaust Duct Required

AMENDMENT
This section has been amended at the state or city level.
Where space for a clothes dryer is provided, an exhaust duct system shall be installed.

Exception: Where a listed condensing clothes dryer is installed prior to occupancy of the structure.

M1502.5 (504.7) Protection Required

AMENDMENT
This section has been amended at the state or city level.
Protective shield plates shall be placed where nails or screws from finish or other work are likely to penetrate the clothes dryer exhaust duct. Shield plates shall be placed on the finished face of framing members where there is less than 11/4 inches (32 mm) between the duct and the finished face of the framing member. Protective shield plates shall be constructed of steel, shall have a minimum thickness of 0.062-inch (1.6 mm) and shall extend not less than 2 inches (51 mm) above sole plates and below top plates.

M1503.1 (505.1) General

AMENDMENT
This section has been amended at the state or city level.
Range hoods shall discharge to the outdoors through a duct. The duct serving the hood shall have a smooth interior surface, shall be air tight, shall be equipped with a back-draft damper and shall be independent of all other exhaust systems. Ducts serving range hoods shall not terminate in an attic or crawl space or areas inside the building.

Exception: Where installed in accordance with the manufacturer's instructions, and where mechanical or natural ventilation is otherwise provided, listed and labeled ductless range hoods shall not be required to discharge to the outdoors.

M1503.2 (505.1) Duct Material

AMENDMENT
This section has been amended at the state or city level.
Ducts serving range hoods shall be constructed of galvanized steel, stainless steel or copper.

Exception: Ducts for domestic kitchen cooking appliances equipped with down-draft exhaust systems shall be permitted to be constructed of schedule 40 PVC pipe and fittings provided that the installation complies with all of the following:
  1. The duct is installed under a concrete slab poured on grade.
  2. The underfloor trench in which the duct is installed is completely backfilled with sand or gravel.
  3. The PVC duct extends not more than 1 inch (25 mm) above the indoor concrete floor surface.
  4. The PVC duct extends not more than 1 inch (25 mm) above grade outside of the building.
  5. The PVC ducts are solvent cemented.

M1503.3 Kitchen Exhaust Rates

AMENDMENT
This section has been amended at the state or city level.

M1503.4 (505.2) Makeup Air Required

AMENDMENT
This section has been amended at the state or city level.
Exhaust hood systems capable of exhausting in excess of 400 cubic feet per minute (0.19 m3/s) shall be provided with makeup air at a rate approximately equal to the exhaust air rate that is in excess of 400 cubic feet per minute (0.19 m3/s). Such makeup air systems shall be equipped with a means of closure and shall be automatically controlled to start and operate simultaneously with the exhaust system. Dampers shall be accessible for inspection, service, repair and replacement without removing permanent construction or any other ducts not connected to the damper being inspected, serviced, repaired or replaced.

Exception: Where all appliances in the house are directvent, power-vent, unvented, or electric, makeup air shall be provided where exhaust fans are capable of exhausting more than 600 cubic feet per minute (0.28 m3/s). Exhaust hood systems capable of exhausting more than 600 cubic feet per minute (0.28 m3/s) shall be provided with makeup air at a rate approximately equal to the exhaust air rate that is in excess of 600 cubic feet per minute (0.28 m3/s).
Kitchen exhaust makeup air shall be discharged into the same room in which the exhaust system is located or into rooms or duct systems that communicate through one or more permanent openings with the room in which such exhaust system is located. Such permanent openings shall have a net cross-sectional area not less than the required area of the makeup air supply openings.

M1504.1 (917.3) Installation of a Microwave Oven Over a Cooking Appliance

AMENDMENT
This section has been amended at the state or city level.
The installation of a listed and labeled cooking appliance or microwave oven over a listed and labeled cooking appliance shall conform to the terms of the upper appliance's listing and label and the manufacturer's installation instructions. The microwave oven shall conform to UL 923.
Domestic open-top broiler units shall have a metal exhaust hood, having a minimum thickness of 0.0157-inch (0.3950 mm) (No. 28 gage) with 1/4 inch (6.4 mm) clearance between the hood and the underside of combustible material or cabinets. A clearance of not less than 24 inches (610 mm) shall be maintained between the cooking surface and the combustible material or cabinet. The hood shall be not less than the width of the broiler unit, extend over the entire unit, discharge to the outdoors and be equipped with a backdraft damper or other means to control infiltration/exfiltration when not in operation. Broiler units incorporating an integral exhaust system, and listed and labeled for use without an exhaust hood, need not have an exhaust hood.
Where exhaust duct construction is not specified in this chapter, construction shall comply with Chapter 16.

M1506.2 Duct Length

AMENDMENT
This section has been amended at the state or city level.
Exhaust duct length shall comply with the manufacturer's design criteria, standard duct airflow design methods, or where the flow rate of the installed ventilating equipment is verified by the installer or approved third party using a flow hood, flow grid or other airflow measuring device.

M1506.3 (501.3.1) Exhaust Openings

AMENDMENT
This section has been amended at the state or city level.
Air exhaust openings shall terminate not less than 3 feet (914 mm) from property lines; 3 feet (914 mm) from operable and nonoperable openings into the building and 10 feet (3048 mm) from mechanical air intakes except where the opening is located 3 feet (914 mm) above the air intake. Openings shall comply with Sections R303.5.2 and R303.6.

M1507.1 General

AMENDMENT
This section has been amended at the state or city level.
Where local exhaust or whole-house mechanical ventilation is required, the equipment shall be designed in accordance with this section. Refer to Section R303.1 for natural ventilation.
Exhaust air from bathrooms and toilet rooms shall not be recirculated within a residence or to another dwelling unit and shall be exhausted directly to the outdoors. Exhaust air from bathrooms and toilet rooms shall not discharge into an attic, crawl space or other areas inside the building.
The whole-house ventilation system shall consist of one or more supply or exhaust fans, or a combination of such, and associated ducts and controls. Local exhaust or supply fans are permitted to serve as such a system. Outdoor air ducts connected to the return side of an air handler shall be considered as providing supply ventilation.
The whole-house mechanical ventilation system shall be provided with controls that enable manual override.

M1507.3.3 (403.3.2) Mechanical Ventilation Rate

AMENDMENT
This section has been amended at the state or city level.
The whole-house mechanical ventilation system shall provide outdoor air at a continuous rate of not less than that determined in accordance with Table M1507.3.3(1).

Exception: The whole-house mechanical ventilation system is permitted to operate intermittently where the system has controls that enable operation for not less than 25-percent of each 4-hour segment and the ventilation rate prescribed in Table M1507.3.3(1) is multiplied by the factor determined in accordance with Table M1507.3.3(2).

TABLE M1507.3.3(1)
CONTINUOUS WHOLE-HOUSE MECHANICAL VENTILATION SYSTEM AIRFLOW RATE REQUIREMENTS
DWELLING UNIT
FLOOR AREA
(square feet)
NUMBER OF BEDROOMS
0 — 1 2 — 3 4 — 5 6 — 7 > 7
Airflow in CFM
< 1,500 30 45 60 75 90
1,501 — 3,000 45 60 75 90 105
3,001 — 4,500 60 75 90 105 120
4,501 — 6,000 75 90 105 120 135
6,001 — 7,500 90 105 120 135 150
> 7,500 105 120 135 150 165

For SI: 1 square foot = 0.0929 m2, 1 cubic foot per minute = 0.0004719 m3/s.


TABLE M1507.3.3(2)
INTERMITTENT WHOLE-HOUSE MECHANICAL VENTILATION RATE FACTORSa, b
RUN-TIME PERCENTAGE IN EACH 4-HOUR
SEGMENT
25% 33% 50% 66% 75% 100%
Factora 4 3 2 1.5 1.3 1.0

a. For ventilation system run time values between those given, the factors are permitted to be determined by interpolation.
b. Extrapolation beyond the table is prohibited.
Local exhaust systems shall be designed to have the capacity to exhaust the minimum air flow rate determined in accordance with Table M1507.4.

TABLE M1507.4
MINIMUM REQUIRED LOCAL EXHAUST RATES FOR ONE- AND TWO-FAMILY DWELLINGS
AREA TO BE
EXHAUSTED
EXHAUST RATES
Kitchens 100 cfm intermittent or 25 cfm continuous
Bathrooms-Toilet
Rooms
Mechanical exhaust capacity of 50 cfm
intermittent or 20 cfm continuous

For SI: 1 cubic foot per minute = 0.0004719 m3/s.

Section M1508 (512) Subslab Soil Exhaust Systems

AMENDMENT
This section has been amended at the state or city level.

M1508.1 (512.1) General

AMENDMENT
This section has been amended at the state or city level.
Where a subslab soil exhaust system is provided, the system shall conform to the requirements of this section.

M1508.2 (512.2) Materials

AMENDMENT
This section has been amended at the state or city level.
Subslab soil exhaust system duct material shall be air duct material listed and labeled to the requirements of UL 181 for Class 0 air ducts, or any of the following piping materials that comply with the International Plumbing Code as building sanitary drainage and vent pipe: cast iron; galvanized steel; brass or copper pipe; copper tube of a weight not less than that of copper drainage tube, Type DWV; and plastic piping.

M1508.3 (512.3) Grade

AMENDMENT
This section has been amended at the state or city level.
Exhaust system ducts shall not be trapped and shall have a minimum slope of one-eighth unit vertical in 12 units horizontal (1-percent slope).

M1508.4 (512.4) Termination

AMENDMENT
This section has been amended at the state or city level.
Subslab soil exhaust system ducts shall extend through the roof and terminate not less than 6 inches (152 mm) above the roof and not less than 10 feet (3048 mm) from any operable openings or air intake.

M1508.5 (512.5) Identification

AMENDMENT
This section has been amended at the state or city level.
Subslab soil exhaust ducts shall be permanently identified within each floor level by means of a tag, stencil or other approved marking.
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