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For buildings where the monthly mean temperature of the building is maintained at not less than 64°F (18°C), footings are not required to extend below the frost line where protected from frost by insulation in accordance with Figure R403.3(1) and Table R403.3(1). Foundations protected from frost in accordance with Figure R403.3(1) and Table R403.3(1) shall not be used for unheated spaces such as porches, utility rooms, garages and carports, and shall not be attached to basements or crawl spaces that are not maintained at a minimum monthly mean temperature of 64°F (18°C).
Materials used below grade for the purpose of insulating footings against frost shall be labeled as complying with ASTM C578.

For SI: 1 inch = 25.4 mm.
  1. See Table R403.3(1) for required dimensions and R-values for vertical and horizontal insulation and minimum footing depth.
FIGURE R403.3(1)

For SI: °C = [(°F) — 32]/1.8.
Note: The air-freezing index is defined as cumulative degree days below 32°F. It is used as a measure of the combined magnitude and duration of air temperature below freezing. The index was computed over a 12-month period (July—June) for each of the 3,044 stations used in the above analysis. Dates from the 1951—80 period were fitted to a Weibull probability distribution to produce an estimate of the 100-year return period.
FIGURE R403.3(2)

TABLE R403.3(1)
PER Figure R403.3(1) (inches)
Along walls At corners A B C
1,500 or less
12 4.5 Not required Not required Not required Not required Not required
14 5.6 Not required Not required Not required Not required Not required
16 6.7 1.7 4.9 12 24 40
16 7.8 6.5 8.6 12 24 40
16 9.0 8.0 11.2 24 30 60
16 10.1 10.5 13.1 24 36 60
For SI: 1 inch = 25.4 mm, °C = [(°F) — 32]/1.8.
  1. Insulation requirements are for protection against frost damage in heated buildings. Greater values could be required to meet energy conservation standards.
  2. See Figure R403.3(2) or Table R403.3(2) for Air-Freezing Index values.
  3. Insulation materials shall provide the stated minimum R-values under long-term exposure to moist, below-ground conditions in freezing climates. The following R-values shall be used to determine insulation thicknesses required for this application: Type II expanded polystyrene (EPS)-3.2 R per inch for vertical insulation and 2.6 R per inch for horizontal insulation; Type IX expanded polystyrene (EPS)-3.4 R per inch for vertical insulation and 2.8 R per inch for horizontal insulation; Types IV, V, VI, VII, and X extruded polystyrene (XPS)-4.5 R per inch for vertical insulation and 4.0 R per inch for horizontal insulation.
  4. Vertical insulation shall be expanded polystyrene insulation or extruded polystyrene insulation.
  5. Horizontal insulation shall be expanded polystyrene insulation or extruded polystyrene insulation.
1,500 or less 2,000 2,500 3,000 3,500 4,000
Alabama All counties
Alaska Ketchikan Gateway, Prince of Wales-Outer Ketchikan (CA), Sitka, Wrangell-Petersburg (CA) Aleutians West (CA), Haines, Juneau, Skagway-Hoonah-Angoon (CA), Yakutat All counties not listed
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Minnesota Houston, Winona All counties not listed Aitkin, Big Stone, Carlton, Crow Wing, Douglas, Itasca, Kanabec, Lake, Morrison, Pine, Pope, Stearns, Stevens, Swift, Todd, Wadena Becker, Beltrami, Cass, Clay, Clearwater, Grant, Hubbard, Kittson, Koochiching, Lake of the Woods, Mahnomen, Marshall, Norman, Otter Tail, Pennington, Polk, Red Lake, Roseau, St. Louis, Traverse, Wilkin
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New Hampshire All counties not listed Carroll, Coos, Grafton
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New Mexico All counties not listed Rio Arriba Colfax, Mora, Taos
New York Albany, Bronx, Cayuga, Columbia, Cortland, Dutchess, Genessee, Kings, Livingston, Monroe, Nassau, New York, Niagara, Onondaga, Ontario, Orange, Orleans, Putnam, Queens, Richmond, Rockland, Seneca, Suffolk, Wayne, Westchester, Yates All counties not listed Clinton, Essex, Franklin, Hamilton, Herkimer, Jefferson, Lewis, St. Lawrence, Warren
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North Dakota Billings, Bowman Adams, Dickey, Golden Valley, Hettinger, LaMoure, Oliver, Ransom, Sargent, Sioux, Slope, Stark All counties not listed
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South Dakota Bennett, Custer, Fall River, Lawrence, Mellette, Shannon, Todd, Tripp Bon Homme, Charles Mix, Davison, Douglas, Gregory, Jackson, Jones, Lyman All counties not listed Beadle, Brookings, Brown, Campbell, Codington, Corson, Day, Deuel, Edmunds, Faulk, Grant, Hamlin, Kingsbury, Marshall, McPherson, Perkins, Roberts, Spink, Walworth
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Utah All counties not listed Box Elder, Morgan, Weber Garfield, Salt Lake, Summit Carbon, Daggett, Duchesne, Rich, Sanpete, Uintah, Wasatch
Vermont Bennington, Grand Isle, Rutland, Windham Addison, Chittenden, Franklin, Orange, Washington, Windsor Caledonia, Essex, Lamoille, Orleans
Virginia All counties
Washington All counties not listed Chelan, Douglas, Ferry, Okanogan
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Wisconsin Kenosha, Kewaunee, Racine, Sheboygan, Walworth All counties not listed Ashland, Barron, Burnett, Chippewa, Clark, Dunn, Eau Claire, Florence, Forest, Iron, Jackson, La Crosse, Langlade, Marathon, Monroe, Pepin, Polk, Portage, Price, Rust, St. Croix, Taylor, Trempealeau, Vilas, Wood Bayfield, Douglas, Lincoln, Oneida, Sawyer, Washburn
Wyoming Goshen, Platte Converse, Crook, Laramie, Niobrara Campbell, Carbon, Hot Springs, Johnson, Natrona, Sheridan, Uinta, Weston Albany, Big Horn, Park, Washakie Fremont, Teton Lincoln, Sublette, Sweetwater
For SI: 1 inch = 25.4 mm.
  1. See Table R403.3(1) for required dimensions and R-values for vertical and horizontal insulation.
FIGURE R403.3(3)

FIGURE R403.3(4)
R403.3.1 Foundations Adjoining Frost-Protected Shallow Foundations
Foundations that adjoin frost-protected shallow foundations shall be protected from frost in accordance with Section R403.1.4.
R403.3.1.1 Attachment to Unheated Slab-on-Ground Structure
Vertical wall insulation and horizontal insulation of frost-protected shallow foundations that adjoin a slab-on-ground foundation that does not have a monthly mean temperature maintained at not less than 64°F (18°C) shall be in accordance with Figure R403.3(3) and Table R403.3(1). Vertical wall insulation shall extend between the frost-protected shallow foundation and the adjoining slab foundation. Required horizontal insulation shall be continuous under the adjoining slab foundation and through any foundation walls adjoining the frost-protected shallow foundation. Where insulation passes through a foundation wall, it shall be either of a type complying with this section and having bearing capacity equal to or greater than the structural loads imposed by the building, or the building shall be designed and constructed using beams, lintels, cantilevers or other means of transferring building loads such that the structural loads of the building do not bear on the insulation.
R403.3.1.2 Attachment to Heated Structure
Where a frost-protected shallow foundation abuts a structure that has a monthly mean temperature maintained at not less than 64°F (18°C), horizontal insulation and vertical wall insulation shall not be required between the frost-protected shallow foundation and the adjoining structure. Where the frost-protected shallow foundation abuts the heated structure, the horizontal insulation and vertical wall insulation shall extend along the adjoining foundation in accordance with Figure R403.3(4) a distance of not less than Dimension A in Table R403.3(1).
Exception: Where the frost-protected shallow foundation abuts the heated structure to form an inside corner, vertical insulation extending along the adjoining foundation is not required.
R403.3.2 Protection of Horizontal Insulation Below Ground
Horizontal insulation placed less than 12 inches (305 mm) below the ground surface or that portion of horizontal insulation extending outward more than 24 inches (610 mm) from the foundation edge shall be protected against damage by use of a concrete slab or asphalt paving on the ground surface directly above the insulation or by cementitious board, plywood rated for below-ground use, or other approved materials placed below ground, directly above the top surface of the insulation.
R403.3.3 Drainage
Final grade shall be sloped in accordance with Section R401.3. In other than Group I Soils, as detailed in Table R405.1, gravel or crushed stone beneath horizontal insulation below ground shall drain to daylight or into an approved sewer system.
R403.3.4 Termite Protection
The use of foam plastic in areas of "very heavy" termite infestation probability shall be in accordance with Section R318.4.

Related Code Sections

R403.3 Foundations, Frost-Protected Shallow Foundations
that adjoin frost-protected shallow foundations shall be protected from frost in accordance with Section R403.1.4 ...