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CHAPTER 3 GENERAL REGULATIONS
1) (Q) A cooling tower is being erected on the roof of a High Rise building. It is being
assembled using parts that are individually listed. Would this installation be allowed
under the 2012 code?
(A) No. The inspector would not allow the installation to be constructed, however, if the
design is sealed by a professional engineer, registered in the State of North Carolina, the
inspector must accept the design and construction of the equipment. Ref: 301.4,
Exception 2, 2012 MC
2) (Q) Exhaust Ductwork is installed on the back wall of a garage extends out about 4 feet
from the wall into the garage area at an elevation of 6 feet above the floor. How
should the ductwork be protected from vehicle damage per code?
(A) Protection may not be required depending on what types of vehicles are worked on in
the garage, however, reflective tape or a bollard would provide adequate protection.
Ref: 303.4, 2012 MC
3) Heating Requirements for Sunrooms
(Q) Are sunrooms exempt from the requirements of the NC Residential Code?
(NCRC), Section R303.8 which requires that all habitable rooms meet certain
design temperatures?
(A) Yes, rooms meeting the definition of “sunroom” are exempt from the
requirements of R303.8. Sunroom is defined by both the NCRC and the NC
Energy Conservation Code (NCECC) generally as “a one story structure
attached to a dwelling with a glazing area in excess of 40% of the gross area of
the structure’s exterior walls and roof”. The North Carolina Mechanical Code,
Section 309.1, requires that “interior spaces intended for human occupancy
shall be provided with active or passive space-heating systems”. However,
there is an exception that excludes spaces where the primary purpose is not
associated with human comfort. This is how DOI addresses sunrooms.
They are considered “outdoor” rooms that are used seasonally and are not
intended to be for human comfort throughout the year. If the structure
attached to the dwelling and opening into the dwelling has glazing less than
40% of the gross area of the structure’s exterior walls and roof, then it is not a
sunroom and is required to conform to the insulation and heating
requirements of the dwelling. R303.8 NCRC
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4) (Q) A barbeque grill has been installed on the covered porch of a residence. The owner has
constructed the hood himself per NSF requirements. Should the hood be allowed by
the Mechanical Inspector?
(A) NO. The grill is an appliance that is listed for outdoor use. To allow the grill to be under
a covered porch, indoors, per code, the grill would have to have a hood built by the
manufacturer of the grill that is approved and compatible with the grill. 304.1, 2012
MC
5) (Q) A tractor trailer has a trailer 11 feet 6 inches high. It is backing into a loading dock
inside a public garage. The ceiling of the garage is 20 feet high. What is the minimum
height to the bottom of the unit heater from the top of the trailer if the unit heater is
installed directly over the trailer?
(A) Unless the manufacturers installation instructions specify a greater height the unit
heater shall be at least 1 foot 6 inches from the top of the trailer to the bottom of the
unit heater. Ref: 304.6, 2012 MC
6) (Q) Can mastic be used in the joints for bonding stacked masonry instead of mortar or
surface bonding cement?
(A) Mastic is required to protect duct joints by adhering to metal duct which is generally
a non porous dry surface when applied. It is not approved for the installation specified
above. 304.1, 304.10.3, 2012 MC
7) (Q) If we are changing out a like for like roof top unit and it is over 16' above the roof does
it have to have permanent access?
(A) A like for like change out will not require the addition of permanent access unless it is
obvious the original approved access has been removed. Ref: 306.5 (2012 NCMC)
8) (Q) I am installing a wood burning stove in my home. When installing the appliance I
will always be able to use table 308.6 for unlisted equipment to reduce clearances.
Is this a true statement?
(A) No. If the solid fuel burning appliance is labeled with clearances those
clearances shall be used when installing the solid-fuel burning appliance. Ref:
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308.7, 2012 MC
9) (Q) What improvement in sizing mechanical equipment for single family dwellings and
duplexes has made it possible in the 2012 code to provide equipment that is properly
sized. (So equipment is not under sized nor is it over sized)?
(A) The use of Manual S for sizing requirements. Ref: 312.1, 2012 MC
CHAPTER 4 VENTILATION
1) (Q) To properly balance air flow and have a constant temperature exchange between all
spaces in an occupied building should ventilation be required at a constant value for
building occupants?
(A) NO. Ventilation shall be provided during the periods that a room or space is occupied.
Ref: 401.3, 2012 MC
2) Situation: We are working on a Nail Salon that will be going in a building downtown.
From speaking with the owner they will not be doing acrylic nails, and nearly all their
products will be organic. In moving forward with the design it has been determined that
per 2012 NCMC (table 403.3 footnote b) we are not allowed to recirculate any air,
therefore, one would think all the air conditioning in the space must be exhausted. This is
not the case per DOI. In conversations with Billy Hinton concerning this section, it is his
interpretation that the reference to, “all air supplied to such spaces” means the
ventilation air supplied, and does not include the air for conditioning the space, therefore,
air for conditioning the space could be returned to the space, but not returned to any
other spaces. Due to the occupancy location on a lower floor of a multi-story building the
designer would like to utilize one of the existing exhaust shafts near the space. One of the
shafts is for toilet exhaust; one shaft is for the pool equipment room. Both exhaust fans
are located on the roof; therefore the shafts are negatively pressurized.
(Q) From reading through Chapter 5 of the code I cannot find any section that will not
allow me to combine the exhaust from the nail salon with either of the existing shafts.
Is this allowed?
(A) Yes. The ventilation requirement for a nail salon, (as determined by 2012 NC
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mechanical code and footnote b in table 404.3), would require mechanical exhaust for
the entire amount of ventilation air supplied for the space for the nail stations. The
code would not require all the conditioned air to be exhausted from the space. The
exhaust from the nail stations may be connected to the exhaust for environmental air
since the system is negatively pressurized. Ref: 403.2.1, Table 403.3 foot note b, 2012
MC
3) (Q) We traded emails recently regarding the 2012 code requirement for exhaust in
residential kitchens, such as apartments and condos. The requirement stems from the
footnotes on the ventilation calculation schedule. I was told by another engineer
recently that Mecklenburg County will not require the kitchen exhaust if we are
utilizing natural ventilation for the apartments.
(A) We have not received an interpretation for the table below from DOI at this time.
For Natural verses Mechanical Ventilation we have sent a clarification document to
list conflicts between the two codes.(See charts below for comparisons) 401.2, 2012
MC vs. R303.4, 2012 Residential Building Code.
(A) We have received the interpretation from Dan Dittman in the 3rd quarter, PE, DOI Chief
Mechanical Engineer on our ventilation comparison chart. I am adding the chart with
DOI answers. The original chart is shown below the DOI chart with answers.
Memo
To: DOI-David Conner/Dan Dittman from Jeff Griffin
Re: Differences in the 2012 NC Mechanical code vs. the 2012 NC Residential Code.
Below is a comparison of the 2 codes (NCRC & NCMC) and the sections related to Natural
Ventilation. There is some language in multiple sections that seem to conflict along with the
available commentary that shows some differences as well. Side by side comparison is listed below
to illustrate, question related to application are listed below.
NCRC (Residential)
NCMC (Mechanical)
R303.1 Habitable rooms. All habitable rooms shall have an
401.2 Ventilation required. Every occupied space shall be
aggregate glazing area of not less than 8 percent of the floor
ventilated by natural means in accordance with Section 402 or
area of such rooms. Natural ventilation shall be through
windows, doors, louvers or other approved openings to the
by mechanical means in accordance with Section 403.
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outdoor air. Such openings shall be provided with ready access
or shall otherwise be readily controllable by the building
occupants. The minimum openable area to the outdoors shall
be 4 percent of the floor area being ventilated.
Exceptions:
1. The glazed areas need not be openable where the opening is
not required by Section R310 and an approved mechanical
ventilation system capable of producing 0.35 air change per
hour in the room is installed or a whole-house mechanical
ventilation system is installed capable of supplying outdoor
ventilation air of 15 cubic feet per minute (cfm) (78 L/s)
per occupant computed on the basis of two occupants
for the first bedroom and one occupant for each additional
bedroom.
HABITABLE SPACE. A space in a building for living,
sleeping, eating or cooking. Bathrooms, toilet rooms, closets,
halls, storage or utility spaces and similar areas are not
considered habitable spaces.
OCCUPIABLE SPACE. An enclosed space intended for
human activities, excluding those spaces intended primarily
for other purposes, such as storage rooms and equipment
rooms, that are only intended to be occupied occasionally and
for short periods of time.
R303.4.1 Intake opening. Mechanical and gravity outdoor
401.4 Intake opening location. Air intake openings shall
air intake openings shall be located a minimum of 10 feet
(3048 mm) from any hazardous or noxious contaminant,
comply with all of the following:
1. Intake openings shall be located a minimum of 10 feet
such as vents, chimneys, plumbing vents, streets, alleys,
parking lots and loading docks, except as otherwise specified
in this code. Where a source of contaminant is located within
10 feet (3048 mm) of an intake opening, such opening shall be
located a minimum of 2 feet (610 mm) below the contaminant
source. For the purpose of this section, the exhaust from
dwelling unit toilet rooms, bathrooms and kitchens shall not be
considered as hazardous or noxious.
(3048 mm) from lot lines or buildings on the same lot.
Where openings front on a street or public way, the distance
shall be measured to the centerline of the street or
public way.
2. Mechanical and gravity outdoor air intake openings shall
be located not less than 10 feet (3048 mm) horizontally
from any hazardous or noxious contaminant source, such
as vents, streets, alleys, parking lots and loading docks,
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except as specified in Item 3 or Section 501.2.1.
3. Intake openings shall be located not less than 3 feet (914
mm) below contaminant sources where such sources are
located within 10 feet (3048 mm) of the opening.
R303.5 Outside opening protection. Air exhaust and intake
401.5 Intake opening protection. Air intake openings that
terminate outdoors shall be protected with corrosion-resistant
openings that terminate outdoors shall be protected with
screens, louvers or grilles. Openings in louvers, grilles and
corrosion-resistant screens, louvers or grilles having a
minimum opening size of 1/4 inch (6 mm) and a maximum
opening size of 1/2 inch (13 mm), in any dimension. Openings
shall be protected against local weather conditions. Outdoor air
exhaust and intake openings shall meet the provisions for
exterior wall opening protectives in accordance with this code.
R303.1 Habitable rooms. All habitable rooms shall have an
aggregate glazing area of not less than 8 percent of the floor
area of such rooms. Natural ventilation shall be through
windows, doors, louvers or other approved openings to the
outdoor air. Such openings shall be provided with ready access
or shall otherwise be readily controllable by the building
occupants. The minimum openable area to the outdoors shall
be 4 percent of the floor area being ventilated.
screens shall be sized in accordance with Table 401.5, and
shall be protected against local weather conditions. Outdoor air
intake openings located in exterior walls shall meet the
provisions for exterior wall opening protectives in accordance
with the International Building Code.
[B] 402.1 Natural ventilation. Natural ventilation of an
occupied space shall be through windows, doors, louvers or
other openings to the outdoors. The operating mechanism for
such openings shall be provided with ready access so that the
openings are readily controllable by the building occupants.
R303.1 Habitable rooms. All habitable rooms shall have an
[B] 402.2 Ventilation area required. The minimum openable
aggregate glazing area of not less than 8 percent of the floor
area to the outdoors shall be 4 percent of the floor area being
area of such rooms. Natural ventilation shall be through
windows, doors, louvers or other approved openings to the
outdoor air. Such openings shall be provided with ready access
or shall otherwise be readily controllable by the building
occupants. The minimum openable area to the outdoors shall
be 4 percent of the floor area being ventilated.
ventilated.
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R303.2 Adjoining rooms. For the purpose of determining
[B] 402.3 Adjoining spaces. Where rooms and spaces without
light and ventilation requirements, any room shall be
considered as a portion of an adjoining room when at least
one-half of the area of the common wall is open and
unobstructed and provides an opening of not less than onetenth of the floor area of the interior room but not less than
25 square feet (2.3 m2).
openings to the outdoors are ventilated through an adjoining
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room, the opening to the adjoining rooms shall be unobstructed
and shall have an area not less than 8 percent of the floor
area of the interior room or space, but not less than 25 square
feet (2.3 m2). The minimum openable area to the outdoors
shall be based on the total floor area being ventilated.
Exception: Openings required for light and/or ventilation
Exception: Exterior openings required for ventilation shall
shall be permitted to open into a thermally isolated sunroom
or patio cover of not less than one-tenth of the floor area of
be permitted to open into a thermally isolated sunroom
addition or patio cover, provided that the openable area
between the sunroom addition or patio cover and the interior
room has an area of not less than 8 percent of the floor area
of the interior room or space, but not less than 20 square feet
(1.86m2). The minimum openable area to the outdoors shall be
the interior room but not less than 20 square feet (2 m2). The
based on the total floor area being ventilated.
addition or patio cover, provided that there is an openable
area between the adjoining room and the sunroom addition
minimum openable area to the outdoors shall be based upon
the total floor area being ventilated.
R303.3 Bathrooms. Bathrooms, water closet compartments
No separate listing for Bathrooms
and other similar rooms shall be provided with aggregate
glazing area in windows of not less than 3 square feet (0.3 m2),
one-half of which must be openable.
Exception: The glazed areas shall not be required where
artificial light and a mechanical ventilation system are
provided. The minimum ventilation rates shall be 50 cubic feet
per minute (24 L/s) for intermittent ventilation or 20 cubic feet
per minute (10 L/s) for continuous ventilation. Ventilation air
from the space shall be exhausted directly to the outside.
Questions:
1. The definitions between the 2 codes are different NCRC uses habitable rooms and the
NCMC uses occupiable spaces. It appears that the NCMC has more requirements than the
NCRC in that bathrooms, toilet rooms, laundry rooms, hallways, and possible closets if using
natural ventilation would be required openings to the exterior that match floor area, NCRC
has natural ventilation minimum opening for bathroom and toilet rooms but NCMC doesn’t.
Does the NCMC require hallways (No, provided the “hallway” is not so large as to
become a Habitable Space, as defined in NCRC Section R304.2 and R304.3), laundry
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rooms(Yes, if it meets the minimum habitable room requirements of NCRC Section
304.3, No, if it is less than that, but in any case makeup air must be provided to the
dryer in accordance with Section 504.5 of the NCMC, and manufacturer’s instructions),
closets(No) and bathroom/toilet rooms(Yes) to have windows to the exterior or adjoining
room option if using natural ventilation?
2. In reference to both codes is a door or window considered an intake opening? With respect
to Natural Ventilation, yes, if it is an exterior door or window.
3. If a door/window is an intake opening is screening required for opening protection. No, in
regards to the NC Building Code, I cannot find any requirement for screens on
windows and doors, going back to 1968, 2002, 2006, or 2009. Section R303.5 require a
minimum opening size of ¼”, and a maximum of ½”. A screen with ¼” openings
would not stop most flies or mosquitoes. However, there may be other State or
Federal Agencies that have requirements. I did a little research and found reference to
Section 8 Housing administered by HUD that may require screens in certain cases, but
I could not find the details.
4. If a door/window is an intake opening, does the lot line or between building requirements
apply to NCRC as listed in the mechanical code (Yes. Windows are not prohibited from
these walls, if not prohibited by other parts of the code like Section R302, but there
must be sufficient ventilation provided by other openings or means), would this be the
interpretation related to potential contaminants. (Yes, please note specific allowances for
Environmental Air, Definitions, and Section 501.2.1, Item 3.)
5. The IRC and the IMC commentary that support the 2012 codes (2009 version) has conflicting
information related to what is a intake opening and when screening is required (Windows)
and Lot line issues. The IMC clearly has requirements for lot lines that the IRC doesn’t talk
about and the IRC has no reference to “except windows and doors” as listed in the IMC
commentary for intake openings. How should this be applied? Please refer to the following
link for an interpretation on a related matter.
http://www.ncdoi.com/osfm/engineering/interpretations4/2012%20residential/0302%20%20location%20on%20lot%20related%20to%20zoning,%20deed%20restrictions%20and%2
0covenants.pdf
By restricting ventilation intake opening from 10’ from a Lot line, it allows
development of property nearby without requiring the existing structure to be rebuilt.
If local ordinances allow a zero-lot line, and the required ventilation intakes are on this
side, and the future residence is built less than 10’ from the lot line, now the existing
structure has ventilation intakes that no longer meet the Code. Windows can be
provided in this wall, where allowed by other parts of the code, they cannot be
considered the sole source of ventilation for the space they serve.
6. Should the requirements match in both codes? It certainly would be nice, but the
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Residential Code is usually tweaked to make it more flexible than the Technical codes.
A petition to rule making either be performed in accordance with Section 202.5 of the
Administrative Code, or through the ICC code-making process.
As a general rule, where there is a difference/discrepancy between the Residential Code and
a referenced Technical Code, please refer to Section R102.4.
NCRC (Residential)
NCMC (Mechanical)
R303.1 Habitable rooms. All habitable rooms shall have an
401.2 Ventilation required. Every occupied space shall be
aggregate glazing area of not less than 8 percent of the floor
ventilated by natural means in accordance with Section 402 or
area of such rooms. Natural ventilation shall be through
windows, doors, louvers or other approved openings to the
outdoor air. Such openings shall be provided with ready access
or shall otherwise be readily controllable by the building
occupants. The minimum open able area to the outdoors shall
be 4 percent of the floor area being ventilated.
by mechanical means in accordance with Section 403.
Exceptions:
1. The glazed areas need not be open able where the opening is
not required by Section R310 and an approved mechanical
ventilation system capable of producing 0.35 air change per
hour in the room is installed or a whole-house mechanical
ventilation system is installed capable of supplying outdoor
ventilation air of 15 cubic feet per minute (cfm) (78 L/s)
per occupant computed on the basis of two occupants
for the first bedroom and one occupant for each additional
bedroom.
HABITABLE SPACE. A space in a building for living,
sleeping, eating or cooking. Bathrooms, toilet rooms, closets,
halls, storage or utility spaces and similar areas are not
considered habitable spaces.
OCCUPIABLE SPACE. An enclosed space intended for
human activities, excluding those spaces intended primarily
for other purposes, such as storage rooms and equipment
rooms, that are only intended to be occupied occasionally and
for short periods of time.
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R303.4.1 Intake opening. Mechanical and gravity outdoor
401.4 Intake opening location. Air intake openings shall
air intake openings shall be located a minimum of 10 feet
(3048 mm) from any hazardous or noxious contaminant,
comply with all of the following:
1. Intake openings shall be located a minimum of 10 feet
such as vents, chimneys, plumbing vents, streets, alleys,
parking lots and loading docks, except as otherwise specified
in this code. Where a source of contaminant is located within
10 feet (3048 mm) of an intake opening, such opening shall be
located a minimum of 2 feet (610 mm) below the contaminant
source. For the purpose of this section, the exhaust from
dwelling unit toilet rooms, bathrooms and kitchens shall not be
considered as hazardous or noxious.
(3048 mm) from lot lines or buildings on the same lot.
Where openings front on a street or public way, the distance
shall be measured to the centerline of the street or
public way.
2. Mechanical and gravity outdoor air intake openings shall
be located not less than 10 feet (3048 mm) horizontally
from any hazardous or noxious contaminant source, such
as vents, streets, alleys, parking lots and loading docks,
except as specified in Item 3 or Section 501.2.1.
3. Intake openings shall be located not less than 3 feet (914
mm) below contaminant sources where such sources are
located within 10 feet (3048 mm) of the opening.
R303.5 Outside opening protection. Air exhaust and intake
401.5 Intake opening protection. Air intake openings that
terminate outdoors shall be protected with corrosion-resistant
openings that terminate outdoors shall be protected with
screens, louvers or grilles. Openings in louvers, grilles and
corrosion-resistant screens, louvers or grilles having a
minimum opening size of 1/4 inch (6 mm) and a maximum
opening size of 1/2 inch (13 mm), in any dimension. Openings
shall be protected against local weather conditions. Outdoor air
exhaust and intake openings shall meet the provisions for
exterior wall opening protectives in accordance with this code.
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screens shall be sized in accordance with Table 401.5, and
shall be protected against local weather conditions. Outdoor air
intake openings located in exterior walls shall meet the
provisions for exterior wall opening protectives in accordance
with the International Building Code.
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R303.1 Habitable rooms. All habitable rooms shall have an
aggregate glazing area of not less than 8 percent of the floor
area of such rooms. Natural ventilation shall be through
windows, doors, louvers or other approved openings to the
outdoor air. Such openings shall be provided with ready access
or shall otherwise be readily controllable by the building
occupants. The minimum openable area to the outdoors shall
be 4 percent of the floor area being ventilated.
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[B] 402.1 Natural ventilation. Natural ventilation of an
occupied space shall be through windows, doors, louvers or
other openings to the outdoors. The operating mechanism for
such openings shall be provided with ready access so that the
openings are readily controllable by the building occupants.
R303.1 Habitable rooms. All habitable rooms shall have an
[B] 402.2 Ventilation area required. The minimum openable
aggregate glazing area of not less than 8 percent of the floor
area to the outdoors shall be 4 percent of the floor area being
area of such rooms. Natural ventilation shall be through
windows, doors, louvers or other approved openings to the
outdoor air. Such openings shall be provided with ready access
or shall otherwise be readily controllable by the building
occupants. The minimum openable area to the outdoors shall
be 4 percent of the floor area being ventilated.
ventilated.
R303.2 Adjoining rooms. For the purpose of determining
[B] 402.3 Adjoining spaces. Where rooms and spaces without
light and ventilation requirements, any room shall be
considered as a portion of an adjoining room when at least
one-half of the area of the common wall is open and
unobstructed and provides an opening of not less than onetenth of the floor area of the interior room but not less than 25
square feet (2.3 m2).
openings to the outdoors are ventilated through an adjoining
room, the opening to the adjoining rooms shall be unobstructed
and shall have an area not less than 8 percent of the floor area
of the interior room or space, but not less than 25 square feet
(2.3 m2). The minimum openable area to the outdoors shall be
based on the total floor area being ventilated.
Exception: Openings required for light and/or ventilation
Exception: Exterior openings required for ventilation shall
shall be permitted to open into a thermally isolated sunroom
or patio cover of not less than one-tenth of the floor area of
be permitted to open into a thermally isolated sunroom
addition or patio cover, provided that the openable area
between the sunroom addition or patio cover and the interior
room has an area of not less than 8 percent of the floor area of
the interior room or space, but not less than 20 square feet
(1.86m2). The minimum openable area to the outdoors shall be
the interior room but not less than 20 square feet (2 m2). The
based on the total floor area being ventilated.
addition or patio cover, provided that there is an openable
area between the adjoining room and the sunroom addition
minimum openable area to the outdoors shall be based upon
the total floor area being ventilated.
R303.3 Bathrooms. Bathrooms, water closet compartments
and other similar rooms shall be provided with aggregate
glazing area in windows of not less than 3 square feet (0.3 m2),
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one-half of which must be openable.
Exception: The glazed areas shall not be required where
artificial light and a mechanical ventilation system are
provided. The minimum ventilation rates shall be 50 cubic feet
per minute (24 L/s) for intermittent ventilation or 20 cubic feet
per minute (10 L/s) for continuous ventilation. Ventilation air
from the space shall be exhausted directly to the outside.
Questions:
7. The definitions between the 2 codes are different NCRC uses habitable rooms and the
NCMC uses occupiable spaces. It appears that the NCMC has more requirements than the
NCRC in that bathrooms, toilet rooms, laundry rooms, hallways, and possible closets if using
natural ventilation would be required openings to the exterior that match floor area, NCRC
has natural ventilation minimum opening for bathroom and toilet rooms but NCMC doesn’t.
Does the NCMC require hallways, laundry rooms, closets and bathroom/toilet rooms to have
windows to the exterior or adjoining room option if using natural ventilation?
8. In reference to both codes is a door or window considered an intake opening?
9. If a door/window is an intake opening is screening required for opening protection.
10. If a door/window is an intake opening, does the lot line or between building requirements
apply to NCRC as listed in the mechanical code, would this be the interpretation related to
potential contaminants.
11. The IRC and the IMC commentary that support the 2012 codes (2009 version) has conflicting
information related to what is a intake opening and when screening is required (Windows)
and Lot line issues. The IMC clearly has requirements for lot lines that the IRC doesn’t talk
about and the IRC has no reference to “except windows and doors” as listed in the IMC
commentary for intake openings. How should this be applied?
12. Should the requirements match in both codes?
4) (Q) Are screens allowed on outside vents?
(A) Yes. 401.5 MC and IBC, sizing Table 401.5, 2012 MC (Exception: Dryer Vents)
5) (Q) We recently discussed the requirement for exhaust/ventilation in a residential
(apartment or condo) kitchen. At that time, you indicated the 100 cfm
exhaust would be required in the residential kitchen(s) per table 403.3 of the 2012
NCMC. I have heard other engineers say they are getting a different interpretation. I
have heard that the exhaust is not required if natural ventilation or mechanical
ventilation is applied to the dwelling unit. Which is correct? We have several projects
in design and in plan review at this time. We received a code comment on one project
that the exhaust is required. However, I want to make sure we follow the correct
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interpretation.
(A) The following informal interpretation was received from Dan Dittman, PE, Chief
Mechanical Engineer on June 22, 2012 per the email I forwarded to him from the
project designer.
Mr. Horton,
I can find no requirements for a hood over a residential range, either gas or electric. There
have been proposals to change it, see the first two pages of the attached .pdf, but no actual
requirement.
I checked the installation instructions for some residential ranges and ovens, and there are no
requirements for a hood. They only show clearance to combustible requirements. If they
install a hood, either recirculation or ducted, it has to be done in a manner prescribed by
code, but there is not a code requirement in a dwelling. The UL 858 listing is required for this
to hold true. Domestic gas ranged need to be listed and labeled for domestic use, See NCFGC
623.3.
6) (Q) This is a follow up answer from Mr. Dittman which is also part of his informal
interpretation. Question: If separate ventilation is not required in question 11 above
would it make a difference if you have an interior kitchen without a window or
opening to the outside? Would ventilation be required in the interior Kitchen since
we have class 2 contaminants even when using the 402 natural ventilation calculations
for a dwelling? Are we confirming no hood or mechanical ventilation is required if you
have the kitchen on an exterior wall with an operable window or permanent opening
to the outside?
Mr. Horton
(A) Our North Carolina Code does not address the level of contamination that is in ASHRAE
which I use in trying to understand the basis for our code.
In a dwelling kitchen with an exterior wall, it is clear that ventilation via the Natural
Ventilation Methods, Section 402, can be used, and nothing more is required.
In a dwelling kitchen that does not have an exterior wall, the NC Code does not
prohibit the dwelling kitchen from being ventilated via Natural Methods, Section 402.
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The ASHRAE 62.1 – 2007 would seem to limit the transfer of air from a domestic
kitchen (class 2 air) into the dwelling, (class 1 air). However, this is in the
mechanical ventilation section of ASHRAE 62.1-2007, and not the natural
ventilation section.
With Natural Ventilation, the code minimums are the size of openings, the
responsibility for performance does not go way, but the designer of record is
accountable for that.
Thanks,
Dan Dittman
(We currently have a formal interpretation from DOI that verifies the informal
Interpretation above)
7) Make-Up Air to Gang Toilet Rooms
(Q) Must gang toilet rooms in commercial buildings be provided directly with
outdoor air for make-up of required exhaust air?
(A) No, Section 401 requires that the supply air be approximately equal to the
exhaust air. In effect, the required ventilation air replaces the transfer air to
the toilet rooms, even though it is brought in through the HVAC supply air
system. 403.1 NCMC 2012
8) Ventilation Rate Requirements
(Q) Must the estimated maximum occupant load from Table 403.3 of the NC
Mechanical Code be used when determining the minimum required outdoor
ventilation air requirements?
(A) No. Section 403.3 requires that ventilation systems be designed to have the
capacity to supply the minimum outdoor airflow rate determined in
accordance with Table 403.3. The occupant density entries in Table 403.3 are
based on empirical data and are reasonably accurate for the typical cases in
each type of occupancy; however, there are actually three acceptable options.
Options:
1) Use the values in Table 403.3.
2) The occupancy shall be determined by an approved engineering analysis.
3) Approved statistical data shall document the accuracy of an alternate
anticipated occupant density. An example of this would be a factory setting
where statistical data shows that the occupant load in the table is much
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higher than would be required for a particular industrial process. 403.3
NCMC 2012
CHAPTER 5 EXHAUSTS SYSTEMS
1) (Q) What would be an adequate amount of make-up air in a residential occupancy if the
dryer is exhausting 50 cfm and the Kitchen hood is exhausting through the roof at the
same time at 40 cfm. How much make- up air would be required?
(A) It depends. Make up air is not required in residential occupancies if natural ventilation
is used per 402, however, if 403 is used then make up air would be required.
Ref: 501.3 exception. 2012 MC
2) (Q) Would environmental air exhaust ever be considered hazardous or noxious per the
Mechanical code?
(A) No. 501.2.1 #3, 2012 MC “Such exhaust shall not be considered hazardous of noxious.”
3) (Q) A garage is installing a ventilation system to avoid consideration by the electrical code
to be a class 1 division 2 area. Should the fan motors be interlocked with the
electrical receptacles and /or equipment/appliances in the garage to shut down the
power to the apparatus above if the ventilation fans lose power?
(A) Yes. “Electrical equipment and appliances used in operations that generate explosive
or flammable vapors, fumes or dusts shall be interlocked with the ventilation system
so that the equipment and appliances cannot be operated unless the ventilation fans
are in operation.” 503.1 MC 2012
4) (Q) A contractor sent an attached cut sheet of the fan being used in a pool chemical
storage room. They claim to have used this model fan for many projects in the
Charlotte area for many years. The exhaust is ducted to the exterior with a makeup air
louver in the door or wall. The electrical inspector, not mechanical, is rejecting the fan.
(a) Is this fan acceptable for this application? (b) Should the mechanical inspector look
at the listing/labeling of the fan?
(A) (a) This fan is not acceptable because it is not rated as non corrosive. The atmosphere in
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a pool chemical storage room is required to be exhausted per the fire code because of
the corrosive nature of pool chemicals. Provide a fan listed as non corrosive by the
manufacturer. (b) The Mechanical Inspector should require the correctly listed fan per
code. Ref; 503.4 (2012 NCMC)
5) Dryer Duct Rated Assembly Membrane Penetrations
(Q) Since Section 504.2 of the NC Mechanical Code prohibits the placement of fire
dampers and smoke dampers in dryer ducts, can a dryer duct penetrate the
membrane of a rated floor/ceiling, roof/ceiling, or wall assembly?
(A) Yes. Items #1 and #2 below are examples of two possible methods to
penetrate the rated assembly. Item #3 shows how one might run the duct
without penetrating the rated assembly.
1) The duct can be wrapped with rated duct wrap from the point that the duct
enters the rated assembly to the point where it leaves the rated assembly
The duct wrap must be listed and labeled for the specific intended use. The
duct wrap must be rated the same as the floor/ceiling assembly,
roof/ceiling, or wall assembly. The penetration must be sealed to prevent
the passage of smoke or flame.
2) If the rated floor/ceiling, roof/ceiling, or wall assembly test report indicates
that penetrations of the assembly membrane by ducts is acceptable, then
the dryer duct may pass through the assembly membrane as prescribed in
the test report unless the report requires dampers. Dampers are never
allowed.
3) Relocate the membrane of the rated floor/ceiling, roof/ceiling, or wall
assembly such that the duct is not within the assembly. 716.6.2 NCBC,
504.2 & 607.6.2 NCMC 2012.
6) (Q) The contractor has the installation instructions for dryer vents for a specific make of
Maytag dryer that will be installed in all the apartments in a 40 unit complex. The
Manufacturers’ instructions show lengths of duct runs that exceed the minimum code
and no equivalent lengths for the fittings used with the dryer duct. Should the
inspector approve the installation?
(A) NO. The inspector should require the contractor to supply an equivalent length chart
for fittings from the manufacturer or re-calculate the runs using the equivalent length
chart in the code (table 504.6.4.1) Ref: 504.6.4.2, 2012 MC
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7) (Q) A mechanical contractor is insulating the makeup air duct to a type 1 hood with
standard fiberglass insulation. He has installed the insulation all the way to the hood.
(a) Would this be allowed by the 2012 mechanical code?
(b) What should be used as an alternate method if this is not allowed?
(A) (a) The standard duct insulation should not be allowed within 18 inches of the hood
because of the heat generated by the hood. 506.3.6, 2012 MC
(b) A rated fire wrap material could be used to wrap the duct within 18 inches of the
hood termination. 506.3.6, exception # 3, 2012 MC
8) (Q) A placard has been provided five feet above the dryer exhaust duct connection on the
wall with the dryer manufacturer’s information for duct equivalent length. Does this
meet the identification requirements of the 2012 code for length identification?
(A) Yes. It would be considered permanent identification. Ref: 504.6.5 MC 2012
9) Listed Type I Hood Clearance to Combustibles
(Q) Can Table 308.6 be used to reduce the clearance requirement in Section 507.9
for a listed Type I kitchen exhaust hood?
(A) Yes. The clearance reduction methods in Table 308.6 are applicable for
equipment and appliances that are not listed for clearance to combustibles.
UL710 is the test standard for listing factory built Type I hoods and is
referenced in Section 507.1. The UL710 standard does not include testing for
clearance to combustibles; therefore the listing does not address clearance to
combustibles. The 18 inch clearance required by Section 507.9 may be reduced
by application of Table 308.6. 308.6, 507.1 and 507.9 NCMC 2012
10) (Q) The 2012 Code would allow, under the exceptions to 507.2.3, two domestic ranges in
dwelling units, churches, schools, day care centers, break areas and similar locations.
The new 2012 code change has no restriction to 4 burners for domestic ranges, you can
have as many burners as the manufacturer provides or even a grill on the domestic
range cook top and meet the code. Would a clubhouse for an apartment complex
require a hood if they install two 5 burner ranges?
(A) We have an interpretation that applies on our web site. The interpretation would allow
a type II hood in an apartment clubhouse occupancy over domestic ranges rather than a
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Type I hood if the cooking would be considered sporadic and non intensive. If two
ranges are installed the cooking capabilities would be considered intensive and the two
ranges would produce large amounts of smoke and grease laden vapors, therefore a
type I hood, not a type II hood, would be required.
Ref: 507.2.1, 507.2.2, 507.2.3 & exception (2012 NCMC)
11) Situation: A restaurant has installed two barbeque cookers under type I hoods which
exhaust high-medium- & low heat cooking appliances. The food services inspector
discovered the cookers and reported it to the Code Enforcement Department.
Answer a. through e. below.
a. (Q) The owner says the cookers are safe as installed and they are code compliant. (1) Is
the owner correct? (2) What are the obvious code violations related to this
installation?
(A) (1) The owner is not qualified to determine the safety of the equipment. The restaurant
installed the cookers without plans or permits. Require cookers to meet the code. Ref:
106.1, 106.2.1 Administrative Code.
(2) Since the cookers use solid fuel and gas for heat for cooking they are classified as
extra-heavy-duty cooking appliances and cannot be located under the same type I
hood with high-medium & low heat appliances. Ref: 507.3.4 MC
b.(Q)Three Type 1 hoods for the cooking equipment are connected to single grease
exhaust duct that exits the building into a covered parking garage. (1) Can the separate
hoods required for the two Extra-heavy-duty cooking appliances be combined with the
existing grease duct exhaust if properly sized? (2) May the grease duct from the extraheavy-duty appliances exhaust into the covered Parking deck?
(A) (1) No. Hoods for the two extra-heavy–duty barbeque cookers shall exit the building
through a separate exhaust duct system. The two cookers may, however, be under the
same Type 1 hood rather than having separate hoods or under a hood or hoods listed
for the application by the manufacturer. The exhaust systems may also be combined
since both are extra-heavy-duty cooking appliances. Ref: 507.2.4, 506.3.5 exception # 4
(2) No. It is a violation to have the current hood system grease duct exiting the building
into a parking garage, unless, it is an open parking garage. If open parking garage then
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terminating in the parking lot with a water wash hood or installing an approved
environmental air unit is used. The new grease duct shall exit the building either
vertically or horizontally to the outside. Ref: 506.3.12.2, 506.3.12.3, 506.5.5
c.(Q) Are there more stringent exhaust requirements for hood exhaust CFM and safety
devices for a hood over an extra-heavy-duty cooking appliance than over high-mediumlow & heat cooking appliances?
(A) Yes, see ventilation tables. Ref: 507.13.1
d.(Q) The manufacturer of the barbeque cookers sends a letter to the Code Administrator
with information on the engineering of the cookers. The letter explains how the cookers
are engineered/designed to make it virtually impossible for a spark or ember to be
exhausted into the duct system. The letter also states the cookers can be located
under the same type I hood with high-medium-low heat cooking appliances. Further, the
letter states the information will be included in the manufacturer’s literature in the
future on the two cookers installed at the restaurant plus 5 other models of cookers with
similar exhaust characteristics. Should the Code Administrator accept the manufacturers
letter and approve the cookers? (note: The manufacturer does not have a registered PE
on their staff.)
(A) The code official may accept the letter under the conditions stated above if a
professional engineer who works directly for the factory provides a letter under his seal
that the changes to the literature will be made. The letter must also provide information
as to how the engineering/design of the product is such that a spark or ember can never
be exhausted from the cookers that may cause a grease fire in the ductwork and ignite
fires in heavy-medium or light duty appliances that may also be under the hood. Ref:
105.2 MC
e. (Q) Should the Code Administrator require a third party test that confirms the cookers
will not emit sparks or embers into the grease duct system before he approves the
cookers?
(A)This may be one solution the Code Administrator would allow. Ref: 105.3, 105.3.1,
105.3.2 (MC).
12) (Q) a. What is the new clearance requirement in the 2012 Mechanical Code from operable
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openings for all environmental air ducts? b. Can environmental air ducts ever be
considered hazardous or noxious?
(A) a. Three feet, Ref: 501.2.1 (MC)
b. No. Ref: 501.2.1 (MC)
13) (Q) Is exhausted air ever allowed to discharge into walkways or hallways?
(A) No. Ref: 501.2.1.1, 2012 MC
14) (Q) Will the mechanical code allow exhaust outlets to discharge at or below the design
flood level (elevation)?
(A) No. 501.2.1 # 4 required 2012 MC, interpreted as required by the 2009
code (2009 501.4 ref. Ch 6, [B] 602.4)
15) (Q) (a) Are all occupancies required to provide pressure equalization when the system is
exhausting quantities of air? (b) Are there specific occupancy exceptions for
appliances and fans and if so what are they?
(A) [note: The 2009 code exempted R 3 occupancies only with no mention of specific
appliances or exhaust exceptions.] (a) The 2012 code exempts dwelling units in R 2
occupancies. (b) The 2012 code does not require pressure equalization for domestic
exhaust systems in residential occupancies and similar uses (domestic clothes dryers,
domestic range hoods, domestic bathroom exhaust). 501.3 and 501.3 exception,
2012 MC
16) (Q) I have a customer with an underground basement. He is going to install an ERV fresh
air ventilator for the basement area. With the situation we are facing we cannot
achieve the 18” ground clearance from grade to the bottom of the ventilator per the
manufacturer’s instructions. We are considering the installation of a dry well.
The manufacturer’s instructions do not say whether or not we can install the exhaust
and intake in a dry well. I have looked through the Residential Code book in sections
401.4, 401.5, 501.2 and 501.2.1. There is no information on this situation. Am I missing
it in the code book? Am I ok to have the builder install a dry well as long as I maintain
the 18” clearance below the opening as required by the manufacturer’s instructions?
(A) We would require a letter from the manufacturer, mailed to the CA, on the
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manufacturers letterhead, signed by the engineer that works for the factory that the
installation would meet ventilation clearance requirements. 505.1 Exception, 105.2,
2012 MC
17) (Q) A Mechanical Contractor is installing a 100 cfm bathroom exhaust fan in the kitchen
ceiling for a new housing development to meet requirements of table 403.3 footnote
b in the 2012 Mechanical Code. He is not installing a kitchen hood over the 4 burner
electric range and the manufacturer does not call for a hood.
Does this installation meet the code for table 403.3 ft. note b requirements of the
2012 Mechanical Code?
(A) Yes. If a mechanical ventilation means is provided per 403.1 MC 2012.
[See 401.2. Ventilation shall be required either by using 402 (Natural Ventilation) or
403 (Mechanical Ventilation).] [See 505.1 Exception 1 “where natural or mechanical
ventilation is “otherwise provided” listed and labeled ductless range hoods shall not
be required to discharge to the outdoors.] Question: If the manufacturer does not
require a hood over the cooking equipment would a ductless hood be required? No.
18) TYPE I HOODS – FINISHING OVENS
(Q) Do electric counter-top conveyor finishing ovens for pizza and other similar
products require a hood, and if so, what type?
(A) NCMC 507.2.1 requires a Type I hood over light-duty cooking appliances and
medium-duty cooking appliances that produce grease or smoke. Therefore, if
smoke or grease from animal or plant oils is produced during cooking with this
appliance, a Type I hood is required. However, if a third-party testing agency
accredited by NC Building Code Council demonstrated that the emissions are
below the levels identified in NFPA 96 2011 4.1.1.1, (reprinted below), and it is
used only for food products that were tested by the test agency, either a Type I
hood or the requirements of NCMC 2012 507.2.2 can be used. The level of
smoke or grease produced is dependent on the food being processed. If the
appliance meets or exceeds the ANSI/UL 197 standard for reduced emissions,
and is installed without a Type I hood, the finishing oven shall be provided with
a permanent placard explaining the food product(s) that the permit was issued
for a change in food product may require a change in hood requirements
References:
NFPA 96 2011
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4.1.1.1* Cooking equipment that has been listed in accordance with ANSI/UL 197 or an
equivalent standard for reduced emissions shall not be required to be provided with an
exhaust system.
4.1.1.2 The listing evaluation of cooking equipment covered by 4.1.1.1 shall demonstrate that
the grease discharge at the exhaust duct of a test hood placed over the appliance shall not
exceed 5 mg/m3, when operated with a total airflow of 500 cfm.
507.2.1 NCMC 2012
19) (Q) Is a Type I or a Type II hood required over an electric egg cooker that operates under
3000 Watts?
(A) No hood is required. Ref: 507.2.2 Exception #4, 2012 MC
20) Project Information: The mechanical design for the a Plant Upgrade consists of the
installation of an air cooled chiller and a chilled water pumping system on the roof adjacent
to the existing air cooled chillers.
The electrical design for this work included an electrical equipment room located within the
garage having a UPS system having closed cell batteries. The electrical equipment room
design has a 2 hour fire rating and includes an air conditioning unit for heat removal with an
exhaust air system, if required, for the removal of hydrogen gas vapors.
The closed cell batteries are limited to the UPS equipment and emit very little hydrogen gas.
As a result, these batteries do not require an exhaust air system by the mechanical code.
However, to be safe, the owner has designed an exhaust air system to protect the electrical
equipment room in the event of an emergency.
The exhaust air system will be normally off and will be controlled by a hydrogen gas detector
installed within the electrical equipment room. When activated, the hydrogen gas detector
will start the exhaust air system and provide a local audio and visual alarm at the electrical
equipment room and at the building BAS system.
The exhaust airflow rate from the electrical equipment room is 150 CFM and it discharges
into the garage which is open to atmosphere for its ventilation air requirements. As a result,
it is our opinion that the exhaust air system is discharging to the outside and that it will have
no impact on the garage environment. The plans examiner has turned the plans down
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requiring the exhaust to go outside the building. He says garage or loading dock is not
considered outside the building per mechanical code. The exhaust duct also has fire dampers
in three locations where it penetrates fire rated walls. The plans examiner will not allow fire
dampers in a hazardous exhaust system and is requiring the installation to be in shaft from
the electrical room to the outside wall penetration.
(Q) What can be done to allow the protection as shown on the plans?
(A) The plans examiner is correct. If your intent is to protect the electrical room from a
possible emergency situation then the installation as described by the plans examiner
is in compliance with minimum code. You have two choices. Meet the code minimums
described or remove the emergency system.
Ref: 510.1, 510.5.7, 510.6.1, 510.6.3 MC 2012
21) (Q) The laboratory exhaust hoods in a hospital room are ducted through a vertical two
hour wall and into a chase that extends between the buildings and up through the roof.
As the designer, I intend to wrap the duct from the penetration in the lab room in 3M
approved 2 hour shaft wrap. The inspector is requiring the exhaust to be wrapped from
the hood all the way to the roof. I see no justification in the code for this requirement.
Is this required by code?
(A) No. The continuous wrapping would be required for a grease duct from a Type I hood.
In discussing this situation with Dan Dittman, the State Mechanical Engineer, it is
required to wrap the non-hazardous lab exhaust duct 10 feet minimum on each side of
a 2 hour rated barrier. A fire damper would not be allowed at the penetration.
In your case the wrap would start 10 feet from the rated wall and run continuously
through the wall and up to the roof penetration. Rated barriers less than one hour are
not defined. (NFPA 4.1.12, 4.1.13) 607.2.2, 510.6.1 MC
22) Performance Test Requirements for Type I Hoods
(Q) What are the performance test requirements for a Type I hood?
(A) Section 507.16 requires a performance test for Type I and Type II hoods. The
testing for a Type I hood shall verify the makeup and exhaust air flow, proper
operation, and capture and containment performance of the exhaust system.
The field test shall be conducted with all appliances under the hood at
operating temperatures, with all sources of outdoor air providing make-up air
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for the hood operating, and with all sources of recirculated air providing
conditioning for the space in which the hood is located operating. Capture and
containment shall be verified visually by observing smoke or steam produced by
actual or simulated cooking, such as with smoke candles, smoke puffers, etc.
The test shall be witnessed by the code official or at the code official’s option by
a professional engineer who shall provide certification of performance to the
code official. 507.16, 507.16.1, 507.16.2 NCMC 2012
CHAPTER 6 DUCT SYSTEMS
1) Plenums versus Habitable Rooms
(Q) Would a habitable room be considered a plenum if it is used as part of the
return air path from an adjacent habitable room or would a habitable room be
considered a plenum if an HVAC unit with a free return is located within the
room?
(A) No, Section 602.1 and Section 202 define a plenum as an enclosed portion of
the building structure that is designed to allow air movement and thereby
serve as part of an air distribution system. Plenums are limited to uninhabited
crawl spaces, areas above a ceiling or below the floor, attic spaces, and
mechanical equipment rooms. The code does not consider a habitable room
intended for human occupancy containing air handling equipment with a free
return to be a plenum space. 602.1 NCMC 2012
2) (Q) DOI, September 1, 2011, 2012 MC
If two or more air-handling systems serve a common space and one or more of these
systems serve additional spaces and the aggregate capacity of the combined systems
exceeds 2,000 cfm, what are the requirements for smoke detectors per Section
606.2.2?
(A) Section 606.2.2 requires that when two or more air systems serve common supply or
return ducts or plenums with a combined design capacity greater than 2000 cfm, the
return system shall be provided with smoked detectors. Section 606.2 states that
smoke detectors are not required where the air distribution system is incapable of
spreading smoke beyond the closing walls, floors and ceiling of the room or space
in which the smoke is generated. If two or more systems serve a common space, but
do not share common ducts or plenums, and each system has a design capacity of
2,000 cfm or less, no smoke detector is required. If their combined design capacity is >
2,000 cfm, and no single unit has a design capacity of 2,000 cfm or more, no smoke
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detector is required because they do not share common ducts or plenums.
If multiple systems share common ducts or plenums and the distribution system is
incapable of spreading smoke beyond the enclosure of the room or space where the
smoke is generated, and then no smoke detector is required.
Keywords: smoke detection system control. 602.2, 2012 MC
3) (Q) Is painting exposed galvanized duct allowed by code for weather protection?
(A) Weather protection would not be required if the ductwork installation is approved by
the manufacturer for outdoor locations. Ref: 303.6, 603.1, MC 2012
4) (Q) Does a filter box have to be manufactured of can it be constructed in the shop of the
Mechanical Contractor?
(A) The Mechanical Contractor may construct the box to meet the code. 603.1, 2012 MC
5) Flexible Air Duct and Air Connector Ground Clearance
(Q) May flexible air ducts or flexible air connectors be run in contact with the
polyethylene installed as a ground cover in a crawl space?
(A) No, Section 603.14 requires that flexible air ducts and connectors not be
located in or within 4 inches of the earth. This would apply to duct installations
in crawl spaces where the ground is or is not covered with polyethylene. 603.14
NCMC 2012
6) (Q) If I have a newly construction house that also has a finished garage that will be
used for a sales center for X amount of years and we run R4.2 flex in the ceiling
of the 1st floor and a section of it passes through the conditioned garage
ceiling, does the R4.2 flex have to be R-8? It's technically in conditioned space is
it not?
(A) If the garage is converted back to a garage then R8 insulation will be required
as a minimum. Section 604 (2012 NCMC) , 405.2 (2012 NCECC)
7) (Q) Two HVAC units are located in an equipment room with one hour fire rated walls. One
wall of the equipment room is common to the corridor wall. The supply and return
ducts both penetrate the membrane of a floor/ceiling assembly in the equipment
room then turn horizontally and penetrate the wall of a fire/smoke rated corridor.
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How should the floor/ceiling membrane be protected? How should the corridor wall
penetration be protected?
(A) The penetration at the membrane should be a rated dynamic fire or radiation damper
approved per UL 555 or UL 555C. The penetration at the corridor wall should be
protected by a fire/smoke damper. Ref: 607.3.1, 607.3.2.3, 607.5 (2012 NCMC)
**Questions 6, 7, and 8 are from questions directed to the Ruskin fire damper manufacturer
representative in the May 29th consistency team meeting.
8) (Q) The first question relates to membrane penetration of a floor /ceiling assembly (not a
through penetration). We are looking for a radiation damper as specified in UL 555 C
with a one hour rating. We cannot find a radiation damper with dynamic closure in one
hour. We know they come in 3 hour radiation dampers but they are cost prohibitive to
install in a one hour membrane. Does any manufacturer produce the one hour dynamic
radiation damper?
(A) Currently, there are no damper manufacturers with a dynamic rated UL 555C ceiling
tested radiation dampers. However, the test standard has recently added criteria
addressing this matter (see below in RED). In regard to the 3-hr radiation damper being
cost prohibitive for a 1-hr membrane, are you referring to wood-constructed ceilings or
non-wood constructed? Yes.
UL 555C
1.3.1 The fire performance measured by ANSI/UL 263 is based upon air movement being
stopped at the start of a fire. Ceiling dampers and ceiling air diffusers intended for use in
HVAC systems where the airflow is operational at the time of a fire, such as in a smoke
control system, or from other situations in which the fan system is operational at the time of
a fire are investigated for dynamic closure. Ceiling dampers and ceiling air diffusers intended
for use where the air movement is effectively stopped at the start of a fire are not required to
be investigated for dynamic closure.
9) (Q) The topic of UL 555 C was brought up as the required listing for radiation type dampers.
It was stated the UL 555 C test was not in the new 2012 North Carolina Mechanical
Code. Is this testing still required?
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(A) Yes the test is still required. The 2012 NC Mechanical code still specifies UL 555 C as the
radiation damper test (607.3.1 2012 code) and dynamic closure is required where air
would still be flowing in the opposite direction of the installation of the radiation
damper in a fire condition.
10) (Q) In the example given in class there was concern when the round base of the radiation
damper was egg shaped after installation. Inspectors typically find this installation
problem. Contractors typically used caulk instead of squaring up the roundness of the
damper base. How should this be properly corrected?
(A) Ruskin would suggest that the damper be “worked” back into shape by the contractor
to avoid the use of caulks and to ensure blades close freely and are not obstructed.
11) (Q) There are existing apartment complexes that are currently permitted and many new
apartments under construction. Can you clarify how plan reviewers and inspectors
should handle these situations?
(A) Yes. See interpretation below.
Problem:
Static radiation dampers installed in the supply duct at the ceiling penetration of floor/ceiling
assemblies in apartment buildings. The particular installation was not code compliant
because a dynamic fire radiation damper would be required by UL 555C. Per UL 555C air
flowing against the static radiation damper from the air handler could cause the damper to
fail open and spread smoke to other areas of the apartment through the supply duct system.
Initial solution approved by the department:
Install a dynamic, shutter type, damper at the ceiling penetration. A dynamic fire radiation
damper could not be found for the installation that met the manufacturer’s installation
requirements for the floor/ceiling assembly membrane penetration. Part of the approval for
the Lloyd and Metal-Fab one hour dampers included an approved mounting detail for the
floor/ceiling assembly membrane since no manufacturers installation detail was shown to
meet the actual installation. A Mechanical Engineer from the project A/E firm provided the
installation detail. We also required a smoke detector as an extra measure of safety to shut
down the unit and required it to be tied in to the apartment smoke detector system.
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DOI ruling:
The procedure above was used for a period of 3 or 4 months from January to April on two
apartment complexes. Prior to April 10th 2012 we contacted Dan Dittman the Mechanical
Chief for DOI. He informed us that we had to use a manufactured, approved, UL 555C
dynamic radiation damper in the supply duct penetration. Mr. Dittman assisted in a search
for the code required damper but one could not be found for any manufacturer. Once this
exercise was completed to his satisfaction Mr. Dittman did consent to allow a standard static
radiation fire damper with a means to shut the unit down to stop air flow from the supply
fan. Mr. Dittman approved the use of a smoke detector to shut the unit down. He also
informed us we could no longer use the Lloyd or Metal-Fab dampers in the membrane
penetration of the floor /ceiling assembly. Mr. Dittman ALLOWED the individual apartment
buildings that were already under construction as of April 10th, 2012 to complete the building
using the Lloyd/Metal-Fab dampers with smoke detectors as originally approved.
Current approved methods:
Currently, individual apartment buildings that started construction after April 10th 2012 are
required to use a one hour dynamic radiation fire damper to meet 607.3.1 and 607.6.2.1 of
the NC 2012 Mechanical Code. A 3 hour dynamic radiation damper may also be used that will
meet the code requirements. If a one hour dynamic radiation damper is not manufactured
and available on the open market the approved alternate method is as follows: use a
standard static one hour radiation damper that meets 607.3.1 and 607.6.2.1 NCMC 2012. The
alternative requirement includes a Smoke Detector either installed in the return at the unit or
located just outside the closet of the HVAC unit to shut the unit down. The smoke detector
located outside the unit enclosure shall be a 120 volt smoke detector with battery backup.
The detectors are not required to be tied into the apartment smoke detector system.
Willis W. Horton, MCP, CBO
Plumbing /Mechanical Code Administrator
Code Enforcement Department
700 N. Tryon St.
Charlotte, NC 28202
Phone: (704) 336-4301/E-mail: Willis.Horton@mecklenburgcountync.gov
12) Fire Damper Access Requirements
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(Q) May flexible duct be allowed to be removed as a method to provide access to
fire dampers as a substitute for fire damper access doors?
(A) No, flexible duct is not allowed to be removed as a method to provide access to
fire dampers as a substitute for fire damper access doors. Access means must
be provided without requiring disassembly of the duct system. Section 607.4
identifies specific requirements for fire damper access. 607.4 NCMC 2012
13) (Q) What method can be used to protect the openings in a floor/ceiling or roof/ceiling
assembly where supply air duct from the HVAC unit penetrates the membrane of the
assembly? The type of occupancy is R2 multi-story with type V construction.
Note: The Mechanical Code calls for either a shaft, 607.6.2 #1, or a listed ceiling
radiation damper installed at the ceiling line, 607.6.2 #2, and a listed ceiling radiation
damper installed at the diffuser with no duct attached 607.6.2 #3 (supply plenum).
(A) There is an issue that needs to be addressed with 607.6.2 #2. UL 555C and 607.3.1
would require the radiation damper to have dynamic closure because the unit fan will
continue to run in a fire or smoke condition. 607.3.1 States; “Only fire dampers listed
or labeled for dynamic systems shall be installed in heating, ventilating, an airconditioning systems designed to operate with fans on during a fire.” There is no
shut down required by code for the fan of an air handler in an apartment HVAC
system for example, therefore, the code and UL 555C require a dynamic type
damper for this installation. Per current DOI information a dynamic radiation damper
listed for mounting in the membrane ceiling of the penetration shall be used. As an
alternate method the air handler must be shut down in case of fire. This can be
accomplished by installing a smoke detector in the room adjacent and open to the air
handler. You are no longer required to tie it into the smoke detector system of the
apartment unit. If you opted for the smoke detector you still are required to protect
the penetration with a radiation damper, however, since you have provided a means to
shut the air down via the smoke detector you can install a standard radiation damper
with static and not dynamic closure. These are the only two methods approved at the
present time. Ref: 607.6.2 #2, 607.3.1, UL 555 C, 2012 MC
CHAPTER 11 REFRIGERATION
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1) (Q) What is the proper procedure to use for changing out the outside condenser only in a
mixed system where the old evaporator continues to be used? Current system
refrigerant is R22 and the new refrigerant will be R 407 C. (Both are Class A1)
(A) Recovered refrigerants shall meet 1102.2.2.2 requirements. 1101.8 notification of
code Official of change of refrigerant. 105.5 equipment re use. 304.1 manufacturers
data req’d. See also 301.1.1, All references in this answer are from the 2012 MC
.
ENERGY CONSERVATION CODE
1) (Q) What are the plan review requirements for compliance with the new energy code
when a plan is submitted for an addition to a single family home to RTAC? The
contractor is submitting plans for an addition. The plans show extending the existing
duct and using the existing HVAC system.
(A) RTAC will not be checking the plans for energy code requirements.
2) (Q) What tools are currently available to help inspectors with Energy Code field
compliance? (Ref. Dept. of Energy information below, will discuss DOI information
under training information later on the agenda)
(A) Per the meeting on energy code on Friday May 18th at the Dept of energy site has both
a residential and commercial checklist for the IECC codes. See the link below.
http://www.energycodes.gov/arra/compliance_checklists.stm
3) (Q) Can a two-story single family dwelling be considered a single HVAC zone?
(A) Yes, subject to a conditional performance requirement. A “Zone” is defined in
Chapter 2 as: A space or group of spaces within a building with heating or
cooling requirements, or both, sufficiently similar so that comfort conditions
can be maintained throughout by a single controlling device.
ACCA (Air Conditioning Contractors of America) Manual D “Residential
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Duct Systems” indicates the maximum allowable temperature difference
between any two rooms in a single zone is 4 degrees Fahrenheit.
202 Definition “Zone” NCECC 2012
4) (Q) (1) Would the 2012 Energy Code require the inspector to witness a duct leakage test
for a single family dwelling? (2) Is a whole house or partial blower door test
required to be witnessed by the inspector?
(A) (1) No. 402.4.2 EC (2) Yes. 4032.2 EC
5) (Q) Does Section 403.1.2 of the 2012 NCSECC require the use of an outdoor
thermostat as a means to prevent supplemental heater operation when the
heat pump alone can satisfy the heating load for a single family dwelling?
(A) Yes, Section 403.1.2 requires a two-stage thermostat with set points that
control supplementary heating on the second stage (lower set point) and
compression heating on the first stage (higher set point). Standard heat pump
thermostats supplied by heat pump manufacturers meet this requirement. Use
of an outside thermostat wired in series with the second stage to lock out the
supplemental heating when the heat pump alone can meet the heating load is
an additional energy conservation measure and is a new requirement in the
2012 NCECC. 403.1.2 NCECC 2012
6) Partial Replacement of a Split System Heat Pump or Air Conditioner
(Q) When the outdoor section of a split system residential heat pump or air
conditioner must be replaced, is the replacement equipment required to
perform at the current efficiency requirements for a new system? Also, what is
the inspector’s responsibility for the replacement equipment?
(A) No, it has been common practice for many years for an outdoor section of a
split system residential heat pump or air conditioner to be replaced due to
failure while retaining the indoor section since it remains suitable for
continued use. The outdoor section may be replaced without requiring
replacement of the indoor section given the replacement outdoor section is
compatible with the indoor section and the pair will function acceptably
together as a system. The inspector is responsible to assure that the
replacement equipment is installed in accordance with the manufacturers
installation instructions. Because the system is not replaced in whole, the
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efficiency requirements for a new system do not apply.
This interpretation follows from a special joint meeting with the Mechanical
Committee Chairman of the NC Building Code Council, Dept. of Insurance
management and staff, inspectors from various jurisdictions, and the State Board of
Plumbing, Heating, and Fire Sprinkler Contractors. 503.2.3 NCECC 2012, 301.4 NCMC
2012
7) Unlisted Duct Tape for Sealing Commercial Duct
(Q) For commercial buildings, can unlisted duct tape be used to seal metal
ductwork?
(A) No. For commercial buildings, Section 503.2.7 requires compliance with Section
603.9 of the 2012 NC Mechanical Code. Section 603.9 of the NC Mechanical
Code requires duct tape to be listed and labeled. 503.2.7 NCECC 2012
8) Process Refrigerant Piping Insulation for Commercial Buildings
(Q) Do the piping insulation requirements of Section 503.2.8 apply to process
refrigerant piping such as for refrigerant piping for walk in coolers or open case
coolers in grocery stores?
(A) No, the refrigerant piping insulation requirements in Section 503.2.8 apply only
to piping serving as part of a building HVAC system. Process piping associated
with other refrigeration processes are not within the scope of the NC Energy
Code. However, the NC Mechanical Code, Section 1107.4 requires that process
refrigerant piping that will reach a surface temperature below the dew point of
the surrounding air, and is located in spaces or areas where condensation will
cause a safety hazard to the building occupants, structure, electrical equipment,
or any other equipment or appliances, shall be protected in an approved
manner to prevent such damage. This may be accomplished by installing
adequate insulation to prevent condensation. 503.2.8 NCECC 2012
GENERAL INFORMATION (Admin. Code/ Mech. Code Admin. Section/ Policy)
1) (Q) Are permits required for B vents when a re-roof permit is pulled for a building with gas
flues penetrating the roof?
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(A) Yes. Alteration of the vent will require a permit. Ref: (102.1/GS 87-21/GS 153-327
Admin. Code), (102.9 2012 MC). A letter is on the Meckpermit.com web site under the
Mechanical Section click on “news and updates” there is a link on that page for the reroof permit requirements.
2) (Q) Unitary equipment is being installed in a hotel room. E.g. ptac unit in a hotel. Are
permits required for this installation?
(A) If this is a like for like change out permits are not required. If it is a new installation it
should have permits and inspections if it has a hidden drain/ electrical connection.
Ref: 106.1 Administrative codes.
3) (Q) What types of installations do not apply to a refrigeration trade or business and are not
required to be installed by a refrigeration contractor?
(A) House Bill 1105 was recently passed by the General Assembly and signed into law by
Governor Perdue. Changes to the law are summarized as follows:
Section 1 provides that “refrigeration trade or business” does not apply to the following: (1)
The installation of self-contained commercial refrigeration units equipped with an original
equipment manufacturer (OEM) molded plug that does not require the opening of service
valves; (2) the replacement of lamps, fuses and door gaskets; and (3) the installation and
servicing of domestic house-hold self-contained refrigeration appliances equipped with an
OEM molded plug connected to suitable receptacles which have been permanently installed
and do not require the opening of service valves.
4) Situation per Designer: A couple of weeks ago we discussed an old (approx. 35 years)
building (approx. 15,000 sq. ft.) utilizing the original hallway for the return. The ceiling is
extremely tight and there is no real room or access or practical method for adding a return
duct. It is served now by a couple of self-contained single zone units utilizing boiler hot water
and condenser water. We want to replace the ancient units with split systems with the AHU
installed in the same mechanical rooms, with condensing units on the roof and utilizing the
same single zones – no changes to ductwork. There is really no other practical/efficient/cost
effective way to replace the ancient units and get rid of the ancient boilers and cooling
towers. We know we need to submit the mechanical, electrical, and structural but really
need to know about the hallway return before we spend a lot of effort and money. When we
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talked before you indicated that this hallway return could be grandfathered since it is very
close to being like-for-like and there is no work other than replacing the central unit.
4)(Q) Can we still utilize the hallways for returns?
(A) Yes. Since you are doing away with an ancient cooling tower and boiler you we will
need a split system with a condenser on the roof. There will be no changes outside of
the mechanical room and roof. The installation will be allowed per the conditions
specified. 105.3, 2012 MC
5) (Q) What are the current requirements for installing Carbon Monoxide detectors in
residential single family dwellings, duplexes and townhomes? Is the requirement
the same for commercial construction?
(A) In general, a change out of fossil fuel equipment in a residence will require the addition
of a Carbon Monoxide Detector per GS. CO2 detectors are currently required adjacent
to each sleeping area per BCC rules. An all electric residence is exempt unless
they currently have an existing attached garage or are adding a new attached garage
or have or are adding a fireplace. If these conditions are present Carbon Monoxide
Detectors are required even if they do not have fossil fuel equipment. Fossil fuel fired
equipment such as a hot water heaters in a hut attached to the house are exempt from
the CO2 detector requirements, however, a gas pack or other appliance that is
communicating with the inside of the house is not exempt. The “special exemptions”
only apply to single family dwellings, duplexes and townhomes. Not required
for commercial occupancies. If a “plug in type or table model” Carbon Monoxide
detector will be used the inspector shall have ready access to the detector on the
premises. It must be in the box and readily accessible for the inspector. Having an
empty box for the inspector or taping a box to the inside of a window is not acceptable.
6) (Q) I would like to get some information from you concerning our HVAC unit replacements.
We currently manage 3 apartment communities in Charlotte and we are considering
trying to have one of our more experienced technicians get a NC license so we can
obtain permits and change out the units ourselves. I contacted Mr. John Todaro of the
NC licensing board and he indicated that once qualifications and fees were met and the
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State exam passed that our tech could get a H3 Class 1 license and that would meet the
State requirements. My question is if there is additional licensing that Mecklenburg
County would require?
(A) We would require a qualified individual to be at the site to answer questions from the
inspector. A journeyman tested and certified through Mecklenburg County would
meet the requirements if the contractor cannot be on the job site.
7) (Q) I have a question about existing equipment. The home owner wants to relocate the
existing air handler in the basement. We are moving the air handler from one room to
another and adjusting the duct work accordingly. I know the duct work that I install to
make the adjustments will have to meet today’s code, but the equipment runs both
the main level and basement and is not zoned. Will I be required to zone this existing
system? Again, I am only moving it from one room to another which is 8’ away from its
current location.
(A) You would not be required to zone the new equipment it would be similar to a like for
like change out. 102.4 (2012 NCMC)
8) (Q) Would a mechanical permit be required for replacing diffusers only? The project
involves making a duct connection to the new diffuser and sealing this connection.
(A) Yes. This is considered new work not maintenance. GS 87-21 # 5
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