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C301.1 General

AMENDMENT
This section has been amended at the state or city level.
In Table C301.1, warm humid counties are identified by an asterisk.

The climate zone for any location outside the United States shall be determined by applying Table C301.3(1) and then Table C301.3(2).

TABLE C301.3(1)

INTERNATIONAL CLIMATE ZONE DEFINITIONS

MAJOR CLIMATE TYPE DEFINITIONS
Marine (C) Definition—Locations meeting all four criteria:
  1. Mean temperature of coldest month between -3°C (27°F) and 18°C (65°F).
  2. Warmest month mean < 22°C (72°F).
  3. At least four months with mean temperatures over 10°C (50°F).
  4. Dry season in summer. The month with the heaviest precipitation in the cold season has at least three times as much precipitation as the month with the least precipitation in the rest of the year. The cold season is October through March in the Northern Hemisphere and April through September in the Southern Hemisphere.
Dry (B) Definition—Locations meeting the following criteria:

Not marine and P in < 0.44 × (TF - 19.5) [Pcm < 2.0 × (TC + 7) in SI units]

where:

P in = Annual precipitation in inches (cm)

T = Annual mean temperature in °F (°C)

Moist (A) Definition—Locations that are not marine and not dry.
Warm-humid Definition—Moist (A) locations where either of the following wet-bulb temperature conditions shall occur during the warmest six consecutive months of the year:
  1. 67°F (19.4°C) or higher for 3,000 or more hours; or
  2. 73°F (22.8°C) or higher for 1,500 or more hours.

For SI: °C = [(°F)-32]/1.8, 1 inch = 2.54 cm.

TABLE C301.3(2)

INTERNATIONAL CLIMATE ZONE DEFINITIONS

ZONE
NUMBER
THERMAL CRITERIA
IP UnitsSI Units
19000 < CDD50°F5000 < CDD10°C
26300 < CDD50°F ≤ 90003500 < CDD10°C ≤ 5000
3A and 3B4500 < CDD50°F ≤ 6300 AND HDD65°F ≤ 54002500 < CDD10°C ≤ 3500 AND HDD18°C ≤ 3000
4A and 4BCDD50°F ≤ 4500 AND HDD65°F ≤ 5400CDD10°C ≤ 2500 AND HDD18°C ≤ 3000
3CHDD65°F ≤ 3600HDD18°C ≤ 2000
4C3600 < HDD65°F ≤ 54002000 < HDD18°C ≤ 3000
55400 < HDD65°F ≤ 72003000 < HDD18°C ≤ 4000
67200 < HDD65°F ≤ 90004000 < HDD18°C ≤ 5000
79000 < HDD65°F ≤ 126005000 < HDD18°C ≤ 7000
812600 < HDD65°F7000 < HDD18°C

For SI: °C = [(°F)-32]/1.8.

The tropical climate zone shall be defined as:

  1. Hawaii, Puerto Rico, Guam, American Samoa, U.S. Virgin Islands, Commonwealth of Northern Mariana Islands; and
  2. Islands in the area between the Tropic of Cancer and the Tropic of Capricorn.
The interior design temperatures used for heating and cooling load calculations shall be a maximum of 72°F (22°C) for heating and minimum of 75°F (24°C) for cooling.
Materials, systems and equipment shall be identified in a manner that will allow a determination of compliance with the applicable provisions of this code.

An R-value identification mark shall be applied by the manufacturer to each piece of building thermal envelope insulation 12 inches (305 mm) or greater in width. Alternatively, the insulation installers shall provide a certification listing the type, manufacturer and R-value of insulation installed in each element of the building thermal envelope. For blown-in or sprayed fiberglass and cellulose insulation, the initial installed thickness, settled thickness, settled R-value, installed density, coverage area and number of bags installed shall be listed on the certification. For sprayed polyurethane foam (SPF) insulation, the installed thickness of the areas covered and R-value of installed thickness shall be listed on the certification. For insulated siding, the R-value shall be labeled on the product's package and shall be listed on the certification. The insulation installer shall sign, date and post the certification in a conspicuous location on the job site.

Exception: For roof insulation installed above the deck, the R-value shall be labeled as required by the material standards specified in Table 1508.2 of the International Building Code.

The thickness of blown-in or sprayed fiberglass and cellulose roof/ceiling insulation shall be written in inches (mm) on markers and one or more of such markers shall be installed for every 300 square feet (28 m2) of attic area throughout the attic space. The markers shall be affixed to the trusses or joists and marked with the minimum initial installed thickness with numbers not less than 1 inch (25 mm) in height. Each marker shall face the attic access opening. Spray polyurethane foam thickness and installed R-value shall be listed on certification provided by the insulation installer.
Insulating materials shall be installed such that the manufacturer's R-value mark is readily observable upon inspection.

U-factors of fenestration products shall be determined as follows:

  1. For windows, doors and skylights, U-factor ratings shall be determined in accordance with NFRC 100.
  2. Where required for garage doors and rolling doors, U-factor ratings shall be determined in accordance with either NFRC 100 or ANSI/DASMA 105.

U-factors shall be determined by an accredited, independent laboratory, and labeled and certified by the manufacturer.

Products lacking such a labeled U-factor shall be assigned a default U-factor from Table C303.1.3(1) or C303.1.3(2). The solar heat gain coefficient (SHGC) and visible transmittance (VT) of glazed fenestration products (windows, glazed doors and skylights) shall be determined in accordance with NFRC 200 by an accredited, independent laboratory, and labeled and certified by the manufacturer. Products lacking such a labeled SHGC or VT shall be assigned a default SHGC or VT from Table C303.1.3(3).

TABLE C303.1.3(1)

DEFAULT GLAZED WINDOW, GLASS DOOR AND SKYLIGHT U-FACTORS

FRAME TYPEWINDOW AND
GLASS DOOR
SKYLIGHT
SingleDoubleSingleDouble
Metal1.200.802.001.30
Metal with Thermal Break1.100.651.901.10
Nonmetal or Metal Clad0.950.551.751.05
Glazed Block0.60

TABLE C303.1.3(2)

DEFAULT OPAQUE DOOR U-FACTORS

DOOR TYPEOPAQUE
U-FACTOR
Uninsulated Metal1.20
Insulated Metal (Rolling)0.90
Insulated Metal (Other)0.60
Wood0.50
Insulated, nonmetal edge, max 45% glazing,
any glazing double pane
0.35

TABLE C303.1.3(3)

DEFAULT GLAZED FENESTRATION SHGC AND VT

SINGLE GLAZEDDOUBLE GLAZEDGLAZED
BLOCK
ClearTintedClearTinted
SHGC0.80.70.70.60.6
VT0.60.30.60.30.6
The thermal resistance (R-value) of insulation shall be determined in accordance with the U.S. Federal Trade Commission R-value rule (CFR Title 16, Part 460) in units of h • ft2 • °F/Btu at a mean temperature of 75°F (24°C).
The thermal resistance (R-value) of insulated siding shall be determined in accordance with ASTM C1363. Installation for testing shall be in accordance with the manufacturer's instructions.
Materials, systems and equipment shall be installed in accordance with the manufacturer's instructions and the International Building Code.
Insulation applied to the exterior of basement walls, crawl space walls and the perimeter of slab-on-grade floors shall have a rigid, opaque and weather-resistant protective covering to prevent the degradation of the insulation's thermal performance. The protective covering shall cover the exposed exterior insulation and extend not less than 6 inches (153 mm) below grade.
Where two or more layers of continuous insulation board are used in a construction assembly, the continuous insulation boards shall be installed in accordance with Section C303.2. Where the continuous insulation board manufacturer's instructions do not address installation of two or more layers, the edge joints between each layer of continuous insulation boards shall be staggered.
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