A4 Below-Grade Walls
For the purpose of Section A1.2, the base assembly is 8 in. medium-weight concrete block with a density of 115 lb/ft3 and solid grouted cores. Continuous insulation is installed on the interior or exterior. In contrast to the U-factor for above-grade walls, the C-factor for below-grade walls does not include R-values for exterior or interior air films or for soil. For insulated walls, the C-factor does include R-0.45 for 0.5 in. gypsum board.
|Framing Type and Depth||Rated R-Value of Insulation Alone||Specified C-Factors
(Wall Only, without Soil and Air Films)
|Exterior Insulation, Continuous and Uninterrupted by Framing|
|Continuous Metal Framing at 24 in. on Center Horizontally|
|1 in. Metal Clips at 24 in. on Center Horizontally and 16 in. Vertically|
- If the below-grade wall is uninsulated or only the cells are insulated:
- If the mass wall has additional insulation:
- For concrete walls, determine the Rc from Table A3.1-2 based on the concrete density and wall thickness. Next, determine the effective R-value for the insulation/framing layer from Table A3.1-4 based on the rated R-value of insulation installed, the thickness of the insulation, and whether it is installed between wood or metal framing or with no framing. Then determine the C-factor by adding the Rc and the effective R-value together and taking the inverse of the total.
- For concrete block walls, determine the Rc from Table A3.1-3 based on the block size, concrete density, degree of grouting in the cells, and whether the cells are insulated. Next, determine the effective R-value for the insulation/framing layer from Table A3.1-4 based on the rated R-value of insulation installed, the thickness of the insulation, and whether it is installed between wood or metal framing or with no framing. Then determine the C-factor by adding the Rc and the effective R-value together and taking the inverse of the total.