Section CA104 Below-Grade Walls and Slabs
Coefficients for below-grade walls are given as U-factors (Btu/h × ft2 × °F of wall area). Coefficients for below-grade slabs are listed as F-factors (Btu/h × ft × °F per lineal foot of slab perimeter).
Below-grade wall U-factors are only valid when used with the accompanying below-grade slab F-factor, and vice versa.
DEFAULT WALL U-FACTORS AND SLAB F-FACTORS FOR BASEMENTS
|BELOW GRADE |
|BELOW GRADE |
|2-Foot Depth Below Grade|
|R-11 Interior w/TB||0.065||0.59|
|R-19 Interior w/TB||0.045||0.59|
|R-21 Interior w/TB||0.042||0.59|
|R-21 + R-5 Interior||0.031||0.68|
|R-21 + R-5 Interior w/TB||0.032||0.59|
|R-21 + R-7 Interior||0.029||0.68|
|R-21 + R-7 Interior w/TB||0.030||0.59|
|3.5-Foot Depth Below Grade|
|R-11 Interior w/TB||0.061||0.55|
|R-19 Interior w/TB||0.042||0.55|
|R-21 Interior w/TB||0.040||0.56|
|R-21 + R-5 Interior||0.030||0.63|
|R-21 + R-5 Interior w/TB||0.031||0.56|
|R-21 + R-7 Interior||0.027||0.63|
|R-21 + R-7 Interior w/TB||0.029||0.56|
|7 Foot Depth Below Grade|
|R-11 Interior w/TB||0.053||0.49|
|R-19 Interior w/TB||0.037||0.50|
|R-21 Interior w/TB||0.035||0.50|
|R-21 + R-5 Interior||0.027||0.56|
|R-21 + R-5 Interior w/TB||0.028||0.51|
|R-21 + R-7 Interior||0.025||0.57|
|R-21 + R-7 Interior w/TB||0.026||0.51|
TB = Thermal Break
For SI: 1 inch = 25.4 mm; 1 foot = 304.8 mm.
All below-grade walls are assumed to be 8-inch (203 mm) concrete. The wall is assumed to extend from the slab upward to the top of the mud sill for the distance specified in Table CA104.1, with 6 inches (152 mm) of concrete wall extending above grade.
Interior insulation is assumed to be fiberglass batts placed in the cavity formed by 2 × 4 framing on 24-inch (610 mm) centers with 1/2-inch (12.7 mm) gypsum board as the interior finish material. Exterior insulation is assumed to be applied directly to the exterior of the below-grade wall from the top of the wall to the footing. The exterior case does not assume any interior framing or sheetrock.
In all cases, the entire wall surface is assumed to be insulated to the indicated nominal level with the appropriate framing and insulation application. Coefficients are listed for wall depths of 2 feet (51 mm), 31/2 feet (89 mm) and 7 feet (178 mm) below grade. Basements shallower than 2 feet (51 mm) should use on-grade slab coefficients.
Coefficients are listed for the following four configurations: