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Chapter 4 Residential Energy Efficiency

Section 401 General

401.1 Scope

This chapter applies to residential buildings.

401.2 Compliance

Projects shall comply with Sections 401, 402.4, 402.5, and 403.1, 403.2.2, 403.2.3, and 403.3 through 403.9 (referred to as the mandatory provisions) and either:
  1. Sections 402.1 through 402.3, 403.2.1 and 404.1 (prescriptive);
  2. Section 405 (performance); or
  3. North Carolina specific REScheck shall be permitted to demonstrate compliance with this code. Envelope requirements may not be traded off against the use of high efficiency heating or cooling equipment. No trade-off calculations are needed for required termite inspection and treatment gaps.

401.3 Certificate

A permanent certificate shall be posted on or in the electrical distribution panel, in the attic next to the attic insulation card, or inside a kitchen cabinet or other approved location. The certificate shall not cover or obstruct the visibility of the circuit directory label, service disconnect label or other required labels. The builder, permit holder, or registered design professional shall be responsible for completing the certificate. The certificate shall list the predominant R-values of insulation installed in or on ceiling/roof, walls, foundation (slab, basement wall, crawlspace wall and floor) and ducts outside conditioned spaces; U-factors for fenestration and the solar heat gain coefficient (SHGC) of fenestration. Where there is more than one value for each component, the certificate shall list the value covering the largest area. The certificate shall indicate whether the building air leakage was visually inspected as required in 402.4.2.1 or provide results of the air leakage testing required in 402.4.2.2.The certificate shall provide results of duct leakage test required in Section 403.2.2. Appendix 1.1 contains a sample certificate.

401.4 Additional Voluntary Criteria for Increasing Residential Energy Efficiency

Appendix 4 contains additional voluntary measures for increasing residential energy efficiency beyond code minimums. Implementation of the increased energy efficiency measures is voluntary at the option of the permit holder. The sole purpose of the appendix is to provide guidance for achieving additional residential energy efficiency improvements that have been evaluated to be those that are most cost effective for achieving an additional 15-20% improvement in energy efficiency beyond code minimums.

Section 402 Building Thermal Envelope

402.1 General (Prescriptive)

402.1.1 Insulation and Fenestration Criteria

The building thermal envelope shall meet the requirements of Table 402.1.1 based on the climate zone specified in Chapter 3.
TABLE 402.1.1
INSULATION AND FENESTRATION REQUIREMENTS BY COMPONENTa
CLIMATE
ZONE		 FENESTRATION
U-FACTORb, I		 SKYLIGHTb
U-FACTOR		 GLAZED
FENESTRATION
SHGCb, e, m		 CEILINGk
R-VALUE		 WOOD
FRAME WALL
R-VALUE		 MASS
WALL
R-VALUEi		 FLOOR
R-VALUE		 BASEMENTc
WALL
R-VALUE		 SLABd
R-VALUE
& DEPTH		 CRAWL
SPACEc
WALL
R-VALUE
3 0.35 0.65 0.30 30 13 5/10 19 10/13f 0 5/13
4 0.35 0.60 0.30 38 or 30
cont.j		 15, 13+2.5h 5/10 19 10/13 10 10/13
5 0.35 0.60 NR 38 or 30
cont.j		 19, 13+5, or
15 + 3e,h		 13/17 30g 10/13 10 10/13
For SI: 1 foot = 304.8 mm.
  1. R-values are minimums. U-factors and SHGC are maximums.
  2. The fenestration U-factor column excludes skylights. The SHGC column applies to all glazed fenestration.
  3. "10/13" means R-10 continuous insulated sheathing on the interior or exterior of the home or R-13 cavity insulation at the interior of the basement wall or crawl space wall.
  4. For monolithic slabs, insulation shall be applied from the inspection gap downward to the bottom of the footing or a maximum of 18 inches below grade whichever is less . For floating slabs, insulation shall extend to the bottom of the foundation wall or 24 inches, whichever is less. R-5 shall be added to the required slab edge R-values for heated slabs.
  5. R-19 fiberglass batts compressed and installed in a nominal 2 × 6 framing cavity is deemed to comply. Fiberglass batts rated R-19 or higher compressed and installed in a 2 × 4 wall is not deemed to comply.
  6. Basement wall insulation is not required in warm-humid locations as defined by Figure N1101.2(1 and 2) and Table N1101.2.
  7. Or insulation sufficient to fill the framing cavity, R-19 minimum.
  8. "13+5" means R-13 cavity insulation plus R-5 insulated sheathing. 15+3 means R-15 cavity insulation plus R-3 insulated sheathing. If structural sheathing covers 25 percent or less of the exterior, insulating sheathing is not required where structural sheathing is used. If structural sheathing covers more than 25 percent of exterior, structural sheathing shall be supplemented with insulated sheathing of at least R-2. 13+2.5 means R-13 cavity insulation plus R-2.5 sheathing.
  9. For Mass Walls, the second R-value applies when more than half the insulation is on the interior of the mass wall.
  10. R-30 shall be deemed to satisfy the ceiling insulation requirement wherever the full height of uncompressed R-30 insulation extends over the wall top plate at the eaves. Otherwise R-38 insulation is required where adequate clearance exists or insulation must extend to either the insulation baffle or within 1" of the attic roof deck.
  11. Table value required except for roof edge where the space is limited by the pitch of the roof, there the insulation must fill the space up to the air baffle.
  12. In addition to the exemption in Section 402.3.3, a maximum of two glazed fenestration product assemblies having a U-factor no greater than 0.55 shall be permitted to be substituted for minimum code compliant fenestration product assemblies without penalty.
  13. In addition to the exemption in Section 402.3.3, a maximum of two glazed fenestration product assemblies having a SHGC no greater than 0.70 shall be permitted to be substituted for minimum code compliant fenestration product assemblies without penalty.

402.1.2 R-Value Computation

Insulation material used in layers, such as framing cavity insulation and insulating sheathing, shall be summed to compute the component R-value. The manufacturer's settled R-value shall be used for blown insulation. Computed R-values shall not include an R-value for other building materials or air films.

402.1.3 U-factor Alternative

An assembly with a U-factor equal to or less than that specified in Table 402.1.3 shall be permitted as an alternative to the R-value in Table 402.1.1.
TABLE 402.1.3
EQUIVALENT U-FACTORSa
CLIMATE
ZONE		 FENESTRATION
U-FACTORe		 SKYLIGHT
U-FACTOR		 CEILING
U-FACTOR		 FRAME
WALL
U-FACTOR		 MASS WALL
U-FACTORb		 FLOOR
U-FACTOR		 BASEMENT
WALL
U-FACTOR		 CRAWL
SPACE
WALL
U-FACTORc
3 0.35 0.65 0.035 0.082 0.141 0.047 0.059 0.136
4 0.35 0.60 0.030 0.077 0.141 0.047 0.059 0.065
5 0.35 0.60 0.030 0.061 0.082 0.033 0.059 0.065
  1. Nonfenestration U-factors shall be obtained from measurement, calculation or an approved source.
  2. When more than half the insulation is on the interior, the mass wall U-factors shall be a maximum of 0.17 in Zone 1, 0.14 in Zone 2, 0.12 in Zone 3, 0.10 in Zone 4 except Marine, and the same as the frame wall U-factor in Marine Zone 4 and Zones 5 through 8.
  3. Basement wall U-factor of 0.360 in warm-humid locations as defined by Table 301.1 and Figure 301.2.
  4. Foundation U-factor requirements shown in Table 402.1.3 include wall construction and interior air films but exclude soil conductivity and exterior air films. U-factors for determining code compliance in accordance with Section 402.1.4 (total UA alternative) of Section 405 (Simulated Performance Alternative) shall be modified to include soil conductivity and exterior air films.
  5. A maximum of two glazed fenestration product assemblies having a U-factor no greater than 0.55 and a SHGC no greater than 0.70 shall be permitted to be substituted for minimum code compliant fenestration product assemblies without penalty. When applying this note and using the REScheck "UA Trade-off" compliance method to allow continued use of the software, the applicable fenestration products shall be modeled as meeting the U-factor of 0.35 and the SHGC of 0.30, as applicable, but the fenestration products actual U-factor and actual SHGC shall be noted in the comments section of the software for documentation of application of this note to the applicable products. Compliance for these substitute products shall be verified compared to the allowed substituted maximum U-value requirement and maximum SHGC requirement, as applicable.

402.1.4 Total UA Alternative

If the total building thermal envelope UA (sum of U-factor times assembly area) is less than or equal to the total UA resulting from using the U-factors in Table 402.1.3 (multiplied by the same assembly area as in the proposed building), the building shall be considered in compliance with Table 402.1.1. The UA calculation shall be done using a method consistent with the ASHRAE Handbook of Fundamentals and shall include the thermal bridging effects of framing materials. The SHGC requirements shall be met in addition to UA compliance.

402.2 Specific Insulation Requirements (Prescriptive)

402.2.1 Ceilings With Attic Spaces

Ceilings with attic spaces over conditioned space shall meet the insulation requirements in Table 402.1.1.

Exceptions:
  1. When insulation is installed in a fully enclosed attic floor system, as described in Appendix 1.2.1, R-30 shall be deemed compliant.
  2. In roof edge and other details such as bay windows, dormers, and similar areas where the space is limited, the insulation must fill the space up to the air baffle.

402.2.2 Ceilings Without Attic Spaces

Where the design of the roof/ceiling assembly, including cathedral ceilings, bay windows and other similar areas, does not allow sufficient space for the required insulation, the minimum required insulation for such roof/ceiling assemblies shall be R-30. This reduction of insulation from the requirements of Section 402.1.1 shall be limited to 500 square feet (46 m2) of ceiling surface area. This reduction shall not apply to the U-factor alternative approach in Section 402.1.3 and the total UA alternative in Section 402.1.4.

402.2.3 Access Hatches and Doors

Horizontal access hatches from conditioned spaces to unconditioned spaces (e.g., attics and crawl spaces) shall be weatherstripped and insulated to an R-10 minimum value, and vertical doors to such spaces shall be weatherstripped and insulated to R-5. Access shall be provided to all equipment that prevents damaging or compressing the insulation. A wood framed or equivalent baffle or retainer is required to be provided when loose fill insulation is installed, the purpose of which is to prevent the loose fill insulation from spilling into the living space when the attic access is opened, and to provide a permanent means of maintaining the installed R-value of the loose fill insulation.

Exceptions:
  1. Pull down stair systems shall be weatherstripped and insulated to an R-5 insulation value such that the insulation does not interfere with proper operation of the stair. Non-rigid insulation materials are not allowed. Additional insulation systems that enclose the stair system from above are allowed. Exposed foam plastic must meet the provisions of the Building Code or Residential Code, respectively.
  2. Full size doors that are part of the building thermal envelope and provide a passageway to unconditioned spaces shall meet the requirements of exterior doors in Section 402.3.4.

402.2.4 Mass Walls

Mass walls for the purposes of this chapter shall be considered above-grade walls of concrete block, concrete, insulated concrete form (ICF), masonry cavity, brick (other than brick veneer), earth (adobe, compressed earth block, rammed earth) and solid timber/logs.

402.2.5 Steel-Frame Ceilings, Walls, and Floors

Steel- frame ceilings, walls and floors shall meet the insulation requirements of Table 402.2.5 or shall meet the U-factor requirements in Table 402.1.3. The calculation of the U-factor for a steel-frame envelope assembly shall use a series-parallel path calculation method.


TABLE 402.2.5
STEEL-FRAME CEILING, WALL AND FLOOR INSULATION (R-VALUE)
WOOD FRAME
R-VALUE REQUIREMENT
COLD-FORMED STEEL
EQUIVALENT R-VALUEa
Steel Truss Ceilingsb
R-30
R-38 or R-30 + 3 or R-26 + 5
R-38
R-49 or R-38 + 3
R-49
R-38 + 5
Steel Joist Ceilingsb
R-30
R-38 in 2 × 4 or 2 × 6 or 2 × 8
R-49 in any framing
R-38
R-49 in 2 × 4 or 2 × 6 or 2 × 8 or 2 × 10
Steel-Framed Wall
R-13
R-13 + 5 or R-15 + 4 or R-21 + 3 or R-0 + 10
R-19
R-13 + 9 or R-19 + 8 or R-25 + 7
R-21
R-13 + 10 or R-19 + 9 or R-25 + 8
Steel Joist Floor
R-13
R-19 in 2 × 6
R-19 + 6 in 2 × 8 or 2 × 10
R-19
R-19 + 6 in 2 × 6
R-19 + 12 in 2 × 8 or 2 × 10
  1. Cavity insulation R-value is listed first, followed by continuous insulation R-value.
  2. Insulation exceeding the height of the framing shall cover the framing.

402.2.6 Floors

Floor insulation shall be installed to maintain permanent contact with the underside of the subfloor decking. The distance between tension support wires or other devices that hold the floor insulation in place against the subfloor shall be no more than 18 inches. In addition, supports shall be located no further than 6 inches from each end of the insulation.

Exception: Enclosed floor cavity such as garage ceilings, cantilevers or buildings on pilings with enclosed floor cavity with the insulation fully in contact with the lower air barrier. In this case, the band boards shall be insulated to maintain thermal envelope continuity.

402.2.7 Basement Walls

Walls associated with conditioned basements shall be insulated from the top of the basement wall down to 10 feet (3048 mm) below grade or to the basement floor, whichever is less. Walls associated with unconditioned basements shall meet this requirement unless the floor overhead is insulated in accordance with Sections 402.1.1 and 402.2.6.

402.2.8 Slab-on-Grade Floors

Slab-on-grade floors with a floor surface less than 12 inches (305 mm) below grade shall be insulated in accordance with Table 402.1.1. The top edge of the insulation installed between the exterior wall and the edge of the interior slab shall be permitted to be cut at a 45-degree (0.79 rad) angle away from the exterior wall. Slab edge insulation shall have 2" termite inspection gap consistent with Appendix 1.2.2 of this code.

402.2.9 Closed Crawl Space Walls

Where the floor above a closed crawl space is not insulated, the exterior crawlspace walls shall be insulated in accordance with Table 402.1.1.

Wall insulation may be located in any combination of the outside and inside wall surfaces and within the structural cavities or materials of the wall system.

Wall insulation requires that the exterior wall band joist area of the floor frame be insulated. Wall insulation shall begin 3 inches (76.2 mm) below the top of the masonry foundation wall and shall extend down to 3 inches (76.2 mm) above the top of the footing or concrete floor, 3 inches(76.2 mm) above the interior ground surface or 24 inches (609.6 mm) below the outside finished ground level, whichever is less. (See Appendix 1.2.2 details)

Termite inspection, clearance, and wicking gaps are allowed in wall insulation systems. Insulation may be omitted in the gap area without energy penalty. The allowable insulation gap widths are listed in Table 402.2.9. If gap width exceeds the allowances, one of the following energy compliance options shall be met:
  1. Wall insulation is not allowed and the required insulation value shall be provided in the floor system.
  2. Compliance shall be demonstrated with energy trade-off methods provided by a North Carolina-specific version of RESCHECK.
TABLE 402.2.9
WALL INSULATION ALLOWANCES
FOR TERMITE TREATMENT AND INSULATION GAPS
MAXIMUM GAP WIDTH (INCHES) INSULATION LOCATION GAP DESCRIPTION
3 Outside Above grade inspection between top of insulation and bottom of siding
6 Outside Below grade treatment
4a Inside Wall inspection between top of insulation and bottom of sill
4a Inside Clearance/wicking space between bottom of insulation and top of ground surface, footing, or concrete floor.

For SI: 1 inch = 25.4mm.
  1. No insulation shall be required on masonry wall of 9 inches in height or less.

402.2.10 Masonry Veneer

Insulation shall not be required on the horizontal portion of the foundation that supports a masonry veneer.

402.2.11 Thermally Isolated Conditioned Sunroom Insulation

The minimum ceiling insulation R-values shall be R-19 in Zones 3 and 4, and R-24 in Zone 5. The minimum wall R-value shall be R-13. New wall(s) separating a sunroom from conditioned space shall meet the building thermal envelope requirements. Floor or slab insulation shall comply with values in Table 402.1.1.

402.2.12 Framed Cavity Walls

The exterior thermal envelope wall insulation shall be installed in contact and continuous alignment with the building envelope air barrier. Insulation shall be free from installation gaps, voids, or compression. For framed walls, the cavity insulation shall be enclosed on all sides with rigid material or an air barrier material. Wall insulation shall be enclosed at the following locations when installed on exterior walls prior to being covered by subsequent construction, consistent with the Appendix 1.2.3 of this code:
  1. Tubs
  2. Showers
  3. Stairs
  4. Fireplace units
Enclosure of wall cavity insulation also applies to walls that adjoin attic spaces by placing a rigid material or air barrier material on the attic space side of the wall on the attic space side of the wall.

402.3 Fenestration. (Prescriptive)

402.3.1 U-factor

An area-weighted average of fenestration products shall be permitted to satisfy the U-factor requirements.

402.3.2 Glazed Fenestration SHGC

An area-weighted average of fenestration products more than 50 percent glazed shall be permitted to satisfy the SHGC requirements.

402.3.3 Glazed Fenestration Exemption

Up to 15 square feet (1.4 m2) of glazed fenestration per dwelling unit shall be permitted to be exempt from U-factor and SHGC requirements in Section 402.1.1. This exemption shall not apply to the U-factor alternative approach in Section 402.1.3 and the Total UA alternative in Section 402.1.4.

402.3.4 Opaque Door Exemption

Opaque doors separating conditioned and unconditioned space shall have a maximum U-factor of 0.35.
Exception: One side-hinged opaque door assembly up to 24 square feet (2.22 m2) in area is exempted from the U-factor requirement in Section 402.1.1. This exemption shall not apply to the U-factor alternative approach in Section 402.1.3 and the total UA alternative in Section 402.1.4.

402.3.5 Thermally Isolated Conditioned Sunroom U-factor and SHGC

The maximum fenestration U-factor shall be 0.40 and the maximum skylight U-factor shall be 0.75. Sunrooms with cooling systems shall have a maximum fenestration SHGC of 0.40 for all glazing.

New windows and doors separating the sunroom from conditioned space shall meet the building thermal envelope requirements. Sunroom additions shall maintain thermal isolation; and shall be served by a separate heating or cooling system, or be thermostatically controlled as a separate zone of the existing system.
Exception: A maximum of two glazed fenestration product assemblies having a U-factor no greater than 0.55 and, when cooling is provided, a SHGC no greater than 0.70 shall be permitted to be substituted for minimum code compliant fenestration product assemblies without penalty.

402.3.6 Replacement Fenestration

Where an entire existing fenestration unit is replaced with a new fenestration product, including frame, sash and glazing, the replacement fenestration unit shall meet the applicable requirements for U-factor and SHGC in Table 402.1.1.

402.4 Air Leakage Control (Mandatory Requirements)

402.4.1 Building Thermal Envelope

The building thermal envelope shall be durably sealed with an air barrier system to limit infiltration. The sealing methods between dissimilar materials shall allow for differential expansion and contraction. For all homes, where present, the following shall be caulked, gasketed, weatherstripped or otherwise sealed with an air barrier material, or solid material consistent with Appendix 1.2.4 of this code:
  1. Blocking and sealing floor/ceiling systems and under knee walls open to unconditioned or exterior space.
  2. Capping and sealing shafts or chases, including flue shafts.
  3. Capping and sealing soffit or dropped ceiling areas.
  4. Sealing HVAC register boots and return boxes to subfloor or drywall.

402.4.2 Air Sealing and Insulation

Building envelope air tightness shall be demonstrated by compliance with Section 402.4.2.1 or 402.4.2.2. Appendix 3 contains optional sample worksheets for visual inspection or testing for the permit holder's use only.

TABLE 402.4.2
AIR BARRIER AND INSULATION INSPECTION COMPONENT CRITERIA
COMPONENT CRITERIA
Ceiling/attic Sealants or gaskets provide a continuous air barrier system joining the top plate of framed walls with either the ceiling drywall or the top edge of wall drywall to prevent air leakage. Top plate penetrations are sealed.
For ceiling finishes that are not air barrier systems such as tongue-and-groove planks, air barrier systems,(for example, taped house wrap), shall be used above the finish.
Note: It is acceptable that sealants or gaskets applied as part of the application of the drywall will not be observable by the code official
Walls Sill plate is gasketed or sealed to subfloor or slab.
Windows and doors Space between window and exterior door jambs and framing is sealed.
Floors
(including above-garage and cantilevered floors)		 Air barrier system is installed at any exposed edge of insulation.
Penetrations Utility penetrations through the building thermal envelope, including those for plumbing, electrical wiring, ductwork, security and fire alarm wiring, and control wiring, shall be sealed.
Garage separation Air sealing is provided between the garage and conditioned spaces. An air barrier system shall be installed between the ceiling system above the garage and the ceiling system of interior spaces.
Duct boots Sealing HVAC register boots and return boxes to subfloor or drywall.
Recessed lighting Recessed light fixtures are air tight, IC rated, and sealed to drywall.
Exception—fixtures in conditioned space.

402.4.2.1 Visual Inspection Option

Building envelope tightness shall be considered acceptable when items providing insulation enclosure in Section 402.2.12 and air sealing in Section 402.4.1 are addressed and when the items listed in Table 402.4.2, applicable to the method of construction, are certified by the builder, permit holder or registered design professional via the certificate in Appendix 1.1.

402.4.2.2 Testing Option

Building envelope tightness shall be considered acceptable when items providing insulation enclosure in Section 402.2.12 and air sealing in Section 402.4.1 are addressed and when tested air leakage is less than or equal to one of the two following performance measurements:
  1. 0.30 CFM50/Square Foot of Surface Area (SFSA)

    or
  2. Five (5) air changes per hour (ACH50)

When tested with a blower door fan assembly, at a pressure of 33.5 psf (50 Pa). A single point depressurization, not temperature corrected, test is sufficient to comply with this provision, provided that the blower door fan assembly has been certified by the manufacturer to be capable of conducting tests in accordance with ASTM E 779-03. Testing shall occur after rough in and after installation of penetrations of the building envelope, including penetrations for utilities, plumbing, electrical, ventilation and combustion appliances. Testing shall be reported by the permit holder, a NC licensed general contractor, a NC licensed HVAC contractor, a NC licensed Home Inspector, a registered design professional, a certified BPI Envelope Professional or a certified HERS rater.

During testing:
  1. Exterior windows and doors, fireplace and stove doors shall be closed, but not sealed;
  2. Dampers shall be closed, but not sealed, including exhaust, backdraft, and flue dampers;
  3. Interior doors shall be open;
  4. Exterior openings for continuous ventilation systems, air intake ducted to the return side of the conditioning system, and energy or heat recovery ventilators shall be closed and sealed;
  5. Heating and cooling system(s) shall be turned off;

    and
  6. Supply and return registers shall not be sealed.

The air leakage information, building air leakage result, tester name, date, and contact information, shall be included on the certificate described in Section 401.3.

For Test Criteria 1 above, the report shall be produced in the following manner: perform the blower door test and record the CFM50. Calculate the total square feet of surface area for the building thermal envelope (all floors, ceilings, and walls including windows and doors, bounding conditioned space) and record the area. Divide CFM50 by the total square feet and record the result. If the result is less than or equal to [0.30 CFM50/SFSA] the envelope tightness is acceptable; or

For Test Criteria 2 above, the report shall be produced in the following manner: Perform a blower door test and record the CFM50. Multiply the CFM50 by 60 minutes to create CFHour50 and record. Then calculate the total conditioned volume of the home and record. Divide the CFH50 by the total volume and record the result. If the result is less than or equal to 5 ACH50 the envelope tightness is acceptable.

402.4.3 Fireplaces

Site-built masonry fireplaces shall have doors and comply with Section R1006 of the North Carolina Residential Code for combustion air.

402.4.4 Fenestration Air Leakage

Windows, skylights and sliding glass doors shall have an air infiltration rate of no more than 0.3 cfm per square foot (1.5 L/s/m2), and swinging doors no more than 0.5 cfm per square foot (2.6 L/s/m2), when tested according to NFRC 400 or AAMA/WDMA/CSA 101/I.S.2/A440 by an accredited (by a body such as IAS or NFRC), independent laboratory and listed and labeled by the manufacturer.
Exception: Site-built windows, skylights and doors.

402.4.5 Recessed Lighting

Recessed luminaires installed in the building thermal envelope shall be sealed to limit air leakage between conditioned and unconditioned spaces. All recessed luminaires shall be IC-rated and labeled as meeting ASTM E 283 when tested at 1.57 psf (75 Pa) pressure differential with no more than 2.0 cfm (0.944 L/s) of air movement from the conditioned space to the ceiling cavity. All recessed luminaires shall be sealed with a gasket or caulk between the housing and the interior wall or ceiling covering.

402.5 Maximum Fenestration U-factor and SHGC (Mandatory Requirements)

The area-weighted average maximum fenestration U-factor permitted using trade-offs from Section 402.1.4 shall be 0.40. Maximum skylight U-factors shall be 0.65 in zones 4 and 5 and 0.60 in zone 3. The area-weighted average maximum fenestration SHGC permitted using trade-offs from Section 405 in Zone 3 shall be 0.50.

Exception: A maximum of two glazed fenestration product assemblies having a U-factor no greater than 0.55 and a SHGC no greater than 0.70 shall be permitted to be substituted for minimum code compliant fenestration product assemblies without penalty.
.

Section 403 Systems

403.1 Controls (Mandatory Requirements)

At least one thermostat shall be provided for each separate heating and cooling system.

403.1.1 Programmable Thermostat

Where the primary heating system is a forced-air furnace, at least one thermostat per dwelling unit shall be capable of controlling the heating and cooling system on a daily schedule to maintain different temperature set points at different times of the day. This thermostat shall include the capability to set back or temporarily operate the system to maintain zone temperatures down to 55°F (13°C) or up to 85°F (29°C).

403.1.2 Heat Pump Supplementary Heat (Mandatory Requirements)

Heat pumps having supplementary electric-resistance heat shall have controls that, except during defrost, prevent supplemental heat operation when the heat pump compressor can meet the heating load.

A heat strip outdoor temperature lockout shall be provided to prevent supplemental heat operation in response to the thermostat being changed to a warmer setting. The lockout shall be set no lower than 35°F and no higher than 40°F.
Exception: In lieu of a heat strip outdoor temperature lockout, the following time and temperature electric- resistance control may be used. After 6 minutes of compressor run time in heat mode, supplemental electric heat shall energize only if the leaving air temperature from the indoor coil is below 90°F. If the indoor coil leaving air temperature exceeds 100°F, supplemental heat shall automatically de-energize, but allow the compressor to continue to operate until the call is satisfied. No thermostat shall initiate supplemental electric heat at any time. Thermostat controlled emergency heat shall not be limited by outdoor temperature. Electric resistance supplemental heat during defrost shall operate normally without limitation.

403.1.3 Maintenance Information

Maintenance instructions shall be furnished for equipment and systems that require preventive maintenance.

403.2 Ducts

403.2.1 Insulation (Prescriptive)

Supply and return ducts in unconditioned space and outdoors shall be in insulated to R-8. Supply ducts inside semi-conditioned space shall be insulated to R-4; return ducts inside conditioned and semi-conditioned space are not required to be insulated. Ducts located inside conditioned space are not required to be insulated other than as may be necessary for preventing the formation of condensation on the exterior of cooling ducts.

403.2.2 Sealing (Mandatory Requirements)

All ducts, air handlers, filter boxes and building cavities used as ducts shall be sealed. Joints and seams shall comply with Part V—Mechanical, Section 603.9 of the North Carolina Residential Code. Duct testing shall be verified by compliance with Section 403.2.2.1 or 403.2.2.2.

403.2.2.1 Total Duct Leakage

Total duct leakage less than or equal to 6 CFM (12 L/min) per 100 ft2(9.29 m2) of conditioned floor area served by that system when tested at a pressure differential of 0.1 inches w.g. (25 Pa) across the entire system, including the manufacturer's air handler enclosure.

During testing:
  1. Block, if present, the ventilation air duct(s) connected to the conditioning system.
  2. The duct air leakage testing equipment shall be attached to the largest return in the system or to the air handler.
  3. The filter shall be removed and the air handler power shall be turned off.
  4. Supply boots or registers and return boxes or grilles shall be taped, plugged, or otherwise sealed air tight.
  5. The hose for measuring the 25 Pascals of pressure differential shall be inserted into the boot of the supply that is nominally closest to the air handler.
  6. Specific instructions from the duct testing equipment manufacturer shall be followed to reach duct test pressure and measure duct air leakage.

403.2.2.2 Duct Leakage to the Outside

Conduct the test using fan pressurization of distribution system and building at a fixed reference pressure for combined supply and return leak. Duct leakage to the outside shall be less than or equal to 6 CFM (12 L/min) per 100 ft2 (9.29 m2) of conditioned floor area served by that system when tested at a pressure differential of 0.1 inches w.g. (25 Pa) across the entire system, relative to the outside, including the manufacturer's air handler enclosure.

During testing:
  1. Block, if present, the ventilation air duct(s) connected to the conditioning system.
  2. The duct air leakage testing equipment shall be attached to the largest return in the system or to the air handler.
  3. The filter shall be removed and the air handler power shall be turned off.
  4. Supply boots or registers and return boxes or grilles shall be taped, plugged, or otherwise sealed air tight or as tight as possible.
  5. The hose for measuring the 25 Pascals of pressure differential shall be inserted into the boot of the supply that is nominally closest to the air handler.
  6. Open all interconnecting doors in the building, close dampers for fireplaces and other operable dampers.
  7. Set up an envelope air moving/flow-regulating/ flow measurement assembly, such as a blower door, following the manufacturer's prescribed procedure.
  8. Specific instructions from the duct testing equipment manufacturer shall be followed to reach duct test pressure and measure duct air leakage used in combination with a blower door. Typical steps are as follows:
    1. Depressurize the ductwork system to 25 Pa using the measurement hose in Step 5 above.
    2. Depressurize the house to 25 Pa using an envelope air moving/flow-regulating/flow measurement assembly, such as a blower door.
    3. Correct the duct pressure to measure 0 Pa of pressure differential between the house and the ductwork system.
    4. Read the CFM of duct leakage using the procedures for the specific equipment being used. (Note that most automatically calculating pressure gauges cannot compute the CFM25 automatically with a duct-to-house difference in pressure of 0 Pa, so the gauge setting should be set to read CFM instead of CFM25.)
Duct testing shall be performed and reported by the permit holder, a NC licensed general contractor, a NC licensed HVAC contractor, a NC licensed Home Inspector, a registered design professional, a certified BPI Envelope Professional or a certified HERS rater. A single point depressurization, not temperature corrected, test is sufficient to comply with this provision, provided that the duct testing fan assembly has been certified by the manufacturer to be capable of conducting tests in accordance with ASTM E 1554-07.

The duct leakage information, including duct leakage result, tester name, date, and contact information, shall be included on the certificate described in Section 401.3.

For the Test Criteria, the report shall be produced in the following manner: perform the HVAC system air leakage test and record the CFM25. Calculate the total square feet of Conditioned Floor Area (CFA) served by that system. Multiply CFM25 by 100, divide the result by the CFA and record the result. If the result is less than or equal to 6 CFM25/100 SF the HVAC system air tightness is acceptable. Appendix 3C contains optional sample worksheets for duct testing for the permit holder's use only.

Exceptions to testing requirements:
  1. Duct systems or portions thereof inside the building thermal envelope shall not be required to be leak tested.
  2. Installation of a partial system as part of replacement, renovation or addition does not require a duct leakage test.

403.2.3 Building Cavities (Mandatory Requirements)

Building framing cavities shall not be used as supply ducts.

403.3 Mechanical System Piping Insulation (Mandatory Requirements)

Mechanical system piping capable of carrying fluids above 105°F (41°C) or below 55°F (13°C) shall be insulated to a minimum of R-3.

403.4 Circulating Hot Water Systems (Mandatory Requirements)

All circulating service hot water piping shall be insulated to at least R-2. Circulating hot water systems shall include an automatic or readily accessible manual switch that can turn off the hot water circulating pump when the system is not in use.

403.5 Mechanical Ventilation (Mandatory Requirements)

Exhausts shall have automatic or gravity dampers that close when the ventilation system is not operating.

403.6 Equipment Sizing and Efficiency (Mandatory Requirements)

403.6.1 Equipment Sizing

Heating and cooling equipment shall be sized in accordance with the North Carolina Mechanical Code.

403.6.2 Equipment Efficiencies

Equipment efficiencies shall comply with the current NAECA minimum standards.

403.7 Systems Serving Multiple Dwelling Units (Mandatory Requirements)

Systems serving multiple dwelling units shall comply with Sections 503 and 504 in lieu of Section 403.

403.8 Snow Melt System Controls (Mandatory Requirements)

Snow- and ice-melting systems, supplied through energy service to the building, shall include automatic controls capable of shutting off the system when the pavement temperature is above 50°F, and no precipitation is falling and an automatic or manual control that will allow shutoff when the outdoor temperature is above 40°F.

403.9 Pools, Inground Permanently Installed Spas (Mandatory)

Pools and inground permanently installed spas shall comply with Sections 403.9.1 through 403.9.3.

403.9.1 Pool Heaters

All heaters shall be equipped with a readily accessible on-off switch that is mounted outside of the heater to allow shutting off the heater without adjusting the thermostat setting. Gas-fired heaters shall not be equipped with constant burning pilot lights.

403.9.2 Time Switches

Time switches or other control method that can automatically turn off and on heaters and pumps according to a preset schedule shall be installed on all heaters and pumps. Heaters, pumps and motors that have built-in timers shall be deemed in compliance with this requirement.
Exceptions:
  1. Where public health standards require 24-hour pump operation.
  2. Where pumps are required to operate solar- and waste-heat-recovery pool heating systems.

403.9.3 Pool Covers

Heated pools and inground permanently installed spas shall be provided with a vapor-retardant cover.

Exception: Pools deriving over 70 percent of the energy for heating from site-recovered energy, such as a heat pump or solar energy source computed over an operating season.

Section 404 Electrical Power and Lighting Systems

404.1 Lighting Equipment

A minimum of 75 percent of the lamps in permanently installed lighting fixtures shall be high-efficacy lamps.

Section 405 Simulated Performance Alternative (Performance)

405.1 Scope

This section establishes criteria for compliance using simulated energy performance analysis. Such analysis shall include heating, cooling, and service water heating energy only. A North Carolina registered design professional is required to perform the analysis if required by North Carolina licensure laws.

405.2 Mandatory Requirements

Compliance with this section requires that the mandatory provisions identified in Section 401.2 be met. All supply and return ducts not inside the building thermal envelope shall be insulated to a minimum of R-8. Supply ducts inside semi-conditioned space shall be insulated to R-4; return ducts inside semi-conditioned space are not required to be insulated.

405.3 Performance-Based Compliance

Compliance based on simulated energy performance requires that a proposed residence (proposed design) be shown to have an annual energy cost that is less than or equal to the annual energy cost of the standard reference design. Energy prices shall be taken from a source approved by the code official, such as the Department of Energy, Energy Information Administration's State Energy Price and Expenditure Report. Code officials shall be permitted to require time-of-use pricing in energy cost calculations.
Exception: The energy use based on source energy expressed in Btu or Btu per square foot of conditioned floor area shall be permitted to be substituted for the energy cost. The source energy multiplier for electricity shall be 3.16. The source energy multiplier for fuels other than electricity shall be 1.1.

405.4 Documentation

405.4.1 Compliance Software Tools

Documentation verifying that the methods and accuracy of the compliance software tools conform to the provisions of this section shall be provided to the code official.

405.4.2 Compliance Report

Compliance software tools shall generate a report that documents that the proposed design complies with Section 405.3. The compliance documentation shall include the following information:
  1. Address or other identification of the residence;
  2. An inspection checklist documenting the building component characteristics of the proposed design as listed in Table 405.5.2(1). The inspection checklist shall show results for both the standard reference design and the proposed design, and shall document all inputs entered by the user necessary to reproduce the results;
  3. Name of individual completing the compliance report; and
  4. Name and version of the compliance software tool.
Exception: Multiple orientations. When an otherwise identical building model is offered in multiple orientations, compliance for any orientation shall be permitted by documenting that the building meets the performance requirements in each of the four cardinal (north, east, south and west) orientations.

405.4.3 Additional Documentation

The code official shall be permitted to require the following documents:
  1. Documentation of the building component characteristics of the standard reference design.
  2. A certification signed by the builder providing the building component characteristics of the proposed design as given in Table 405.5.2(1).
  3. Documentation of the actual values used in the software calculations for the proposed design.

405.5 Calculation Procedure

405.5.1 General

Except as specified by this section, the standard reference design and proposed design shall be configured and analyzed using identical methods and techniques.

405.5.2 Residence Specifications

The standard reference design and proposed design shall be configured and analyzed as specified by Table 405.5.2(1). Table 405.5.2(1) shall include by reference all notes contained in Table 402.1.1.

TABLE 405.5.2(1)
SPECIFICATIONS FOR THE STANDARD REFERENCE AND PROPOSED DESIGNS
BUILDING COMPONENT STANDARD REFERENCE DESIGN PROPOSED DESIGN
Above-grade walls Type: mass wall if proposed wall is mass; otherwise wood frame. As proposed
Gross area: same as proposed As proposed
U-factor: from Table 402.1.3 As proposed
Solar absorptance = 0.75 As proposed
Remittance = 0.90 As proposed
Basement and crawl space walls Type: same as proposed As proposed
Gross area: same as proposed As proposed
U-factor: from Table 402.1.3, with insulation layer on interior side of walls. As proposed
Above-grade floors Type: wood frame As proposed
Gross area: same as proposed As proposed
U-factor: from Table 402.1.3 As proposed
Ceilings Type: wood frame As proposed
Gross area: same as proposed As proposed
U-factor: from Table 402.1.3 As proposed
Roofs Type: composition shingle on wood sheathing As proposed
Gross area: same as proposed As proposed
Solar absorptance = 0.75 As proposed
Emittance = 0.90 As proposed
Attics Type: vented with aperture = 1 ft2 per 300 ft2 ceiling area As proposed
Foundations Type: same as proposed foundation As proposed
wall area above and below grade and soil characteristics: same as proposed. As proposed
Doors Area: 40 ft2 As proposed
Orientation: North As proposed
U-factor: same as fenestration from Table 402.1.3. As proposed
Fenestrationb Total areab, c =
  1. The proposed fenestration area; where proposed fenestration area is less than 15% of the conditioned floor area.
  2. 15% of the conditioned floor area; where the proposed fenestration area is 15% or more of the conditioned floor area.
 As proposed
Orientation: equally distributed to four cardinal compass orientations (N, E, S & W). As proposed
U-factor: from Table 402.1.3 As proposed
SHGC: From Table 402.1.1 As proposed
Interior shade fraction:
  1. Summer (all hours when cooling is required) = 0.90
  2. Winter (all hours when heating is required) = 0.90c
 Same as standard reference designd
External shading: none As proposed
Skylights None As proposed
Thermally isolated sunrooms None As proposed
Air exchange rate 5 ACH50

The mechanical ventilation rate shall be in addition to the air leakage rate and the same as in the proposed design, but no greater than continuous operation at 0.01 × CFA + 7.5 (Nbr + 1) where:

CFA = conditioned floor area

Nbr = number of bedrooms

Energy recovery shall not be assumed for mechanical ventilation. 		For residences that are not tested, the same as the standard reference design. For tested residences, the measured air exchange rate.e The mechanical ventilation rate shall be in addition to the air leakage rate and shall be as proposed.f
Mechanical ventilation None, except where mechanical ventilation is specified by the proposed design, in which case:

Annual vent fan energy use:
kWh/yr = 0.03942 × CFA + 29.565 × (Nbr +1)

where:
CFA = conditioned floor area

Nbr = number of bedrooms 		As proposed
Internal gains
IGain = 17,900 + 23.8 × CFA + 4104 × Nbr + ΔIGlighting
(Btu/day per dwelling unit)


Where ΔIGlighting represents the reduced internal gains from efficient lighting as defined by the lighting building component. 		IGain = 17,900 + 23.8 × CFA + 4104 × Nbr + ΔIGlighting
(Btu/day per dwelling unit)

Where ΔIGlighting represents the reduced internal gains from efficient lighting as defined by the lighting building component.
Structural mass For masonry floor slabs, 80% of floor area covered by R-2 carpet and pad, and 20% of floor directly exposed to room air. As proposed
For masonry basement walls, as proposed, but with insulation required by Table 402.1.3 located on the interior side of the walls As proposed
For other walls, for ceilings, floors, and interior walls, wood frame construction As proposed
Heating systemsg, h, i, j As proposed

Capacity: sized in accordance with the North Carolina Mechanical Code and North Carolina Residential Code.

Fuel type: same as proposed design
As proposed
Cooling systems g, i, j, k As proposed

Capacity: sized in accordance with the North Carolina Mechanical Code and North Carolina Residential Code.		 As proposed
Service water heatingi
As proposed

Fuel type: Use: same as proposed design		 As proposed

gal/day = 30 + (10 x Nbr)
Thermal distribution systems A thermal distribution system efficiency (DSE) of 0.88 shall be applied to both the heating and cooling system efficiencies for all systems other than tested duct systems. Duct insulation: From Section 403.2.1. For tested duct systems, the leakage rate shall be the applicable maximum rate from Section 403.2.2. As tested or as specified in Table 405.5.2(2) if not tested
Thermostat Type: Manual, cooling temperature setpoint = 75°F;
Heating temperature setpoint = 72°F
Same as standard reference
Lighting kWh/yr = (455 + 0.80*CFA) + ΔkWh/yr

where:

ΔkWh/yr = [29.5 — 0.5189*CFA*50% — 295.12*50% + 0.0519*CFA]

Internal gains in the Standard Reference Design shall be reduced by 90% of the impact from efficient lighting, calculated in Btu/day using the following equation:

ΔIGlighting = -0.90*ΔkWh/yr*106/293/365 		kWh/yr = (455 + 0.80 CFA) + ΔkWh/yr

where:
ΔkWh/yr = [29.5 — 0.5189*CFA *FL% — 295.12*FL% + 0.0519*CFA]

FL% = the ratio of qualifying light fixtures to all light fixtures in qualifying light fixture locations.

The proposed design shall not have FL% more than 50% from CFL.

Internal gains in the proposed design shall be reduced by 90% of the impact from efficient lighting, calculated in Btu/day using the following equation:

ΔIGlighting =0.90*ΔkWh/yr* 106/293/ 365

For SI: 1 square foot = 0.93 m2; 1 British thermal unit = 1055 J; 1 pound per square foot = 4.88 kg/m2; 1 gallon (U.S.) = 3.785 L; °C = (°F-3)/1.8, 1 degree = 0.79 rad.
  1. Glazing shall be defined as sunlight-transmitting fenestration, including the area of sash, curbing or other framing elements, that enclose conditioned space. Glazing includes the area of sunlight-transmitting fenestration assemblies in walls bounding conditioned basements. For doors where the sunlight-transmitting opening is less than 50 percent of the door area, the glazing area is the sunlight transmitting opening area. For all other doors, the glazing area is the rough frame opening area for the door including the door and the frame.
  2. For residences with conditioned basements, R-2 and R-4 residences and townhouses, the following formula shall be used to determine glazing area:

    AF = As × FA × F

    where:
    AF = Total glazing area.

    As = Standard reference design total glazing area.

    FA = (Above-grade thermal boundary gross wall area)/(above-grade boundary wall area + 0.5 × below-grade boundary wall area).

    F = (Above-grade thermal boundary wall area)/(above-grade thermal boundary wall area + common wall area) or 0.56, whichever is greater.

    and where:
    Thermal boundary wall is any wall that separates conditioned space from unconditioned space or ambient conditions.

    Above-grade thermal boundary wall is any thermal boundary wall component not in contact with soil.

    Below-grade boundary wall is any thermal boundary wall in soil contact.

    Common wall area is the area of walls shared with an adjoining dwelling unit.
  3. For fenestrations facing within 15 degrees (0.26 rad) of true south that are directly coupled to thermal storage mass, the winter interior shade fraction shall be permitted to be increased to 0.95 in the proposed design.
  4. Where leakage area (L) is defined in accordance with Section 5.1 of ASHRAE 119 and where:

    SLA = L/CFA

    where L and CFA are in the same units.
  5. Tested envelope leakage shall be determined and documented by an independent party approved by the code official. Hourly calculations as specified in the 2001 ASHRAE Handbook of Fundamentals, Chapter 26, page 26.21, Equation 40 (Sherman-Grimsrud model) or the equivalent shall be used to determine the energy loads resulting from infiltration.
  6. The combined air exchange rate for infiltration and mechanical ventilation shall be determined in accordance with Equation 43 of 2001 ASHRAE Handbook of Fundamentals, page 26.24 and the "Whole-house Ventilation" provisions of 2001 ASHRAE Handbook of Fundamentals, page 26.19 for intermittent mechanical ventilation.
  7. Thermal storage element shall mean a component not part of the floors, walls or ceilings that is part of a passive solar system, and that provides thermal storage such as enclosed water columns, rock beds, or phase-change containers. A thermal storage element must be in the same room as fenestration that faces within 15 degrees (0.26 rad) of true south, or must be connected to such a room with pipes or ducts that allow the element to be actively charged.
  8. For a proposed design with multiple heating, cooling or water heating systems using different fuel types, the applicable standard reference design system capacities and fuel types shall be weighted in accordance with their respective loads as calculated by accepted engineering practice for each equipment and fuel type present.
  9. For a proposed design without a proposed heating system, a heating system with the prevailing federal minimum efficiency shall be assumed for both the standard reference design and proposed design. For electric heating systems, the prevailing federal minimum efficiency air-source heat pump shall be used for the standard reference design.
  10. For a proposed design home without a proposed cooling system, an electric air conditioner with the prevailing federal minimum efficiency shall be assumed for both the standard reference design and the proposed design.
  11. For a proposed design with a nonstorage-type water heater, a 40-gallon storage-type water heater with the prevailing federal minimum energy factor for the same fuel as the predominant heating fuel type shall be assumed. For the case of a proposed design without a proposed water heater, a 40-gallon storage-type water heater with the prevailing federal minimum efficiency for the same fuel as the predominant heating fuel type shall be assumed for both the proposed design and standard reference design.
TABLE 405.5.2(2)
DEFAULT DISTRIBUTION SYSTEM EFFICIENCIES FOR PROPOSED DESIGNSa
DISTRIBUTION SYSTEM CONFIGURATION AND CONDITION: FORCED AIR SYSTEMS HYDRONIC SYSTEMSb
Distribution system components located in unconditioned space — 0.95
Untested distribution systems entirely located in conditioned spacec 0.88 1
"Ductless" systemsd 1 —

For SI: 1 cubic foot per minute = 0.47 L/s; 1 square foot = 0.093 m2; 1 pound per square inch = 6895 Pa; 1 inch water gauge = 1250 Pa.
  1. Default values given by this table are for untested distribution systems, which must still meet minimum requirements for duct system insulation.
  2. Hydronic systems shall mean those systems that distribute heating and cooling energy directly to individual spaces using liquids pumped through closed loop piping and that do not depend on ducted, forced airflow to maintain space temperatures.
  3. Entire system in conditioned space shall mean that no component of the distribution system, including the air handler unit, is located outside of the conditioned space.
  4. Ductless systems shall be allowed to have forced airflow across a coil but shall not have any ducted airflow external to the manufacturer's air handler enclosure.

405.6 Calculation Software Tools

405.6.1 Minimum Capabilities

Calculation procedures used to comply with this section shall be software tools capable of calculating the annual energy consumption of all building elements that differ between the standard reference design and the proposed design and shall include the following capabilities:
  1. Computer generation of the standard reference design using only the input for the proposed design. The calculation procedure shall not allow the user to directly modify the building component characteristics of the standard reference design.
  2. Calculation of whole-building (as a single zone) sizing for the heating and cooling equipment in the standard reference design residence in accordance with the North Carolina Mechanical Code.
  3. Calculations that account for the effects of indoor and outdoor temperatures and part-load ratios on the performance of heating, ventilating and air-conditioning equipment based on climate and equipment sizing.
  4. Printed code official inspection checklist listing each of the proposed design component characteristics from Table 405.5.2(1) determined by the analysis to provide compliance, along with their respective performance ratings (e.g., R-value, U-factor, SHGC, HSPF, AFUE, SEER, EF, etc.).

405.6.2 Specific Approval

Performance analysis tools meeting the applicable sections of Section 405 shall be permitted to be approved. Tools are permitted to be approved based on meeting a specified threshold for a jurisdiction. The code official shall be permitted to approve tools for a specified application or limited scope.

405.6.3 Input Values

When calculations require input values not specified by Sections 402, 403, 404 and 405, those input values shall be taken from an approved source.