Thermal mass factors for ICF walls in the MEC and Manual J

Insulated concrete form (ICF) systems use a prefabricated form made of foam insulation that is assembled into walls at the building site and filled with concrete. ICFs are available from more than 20 manufacturers, and their use in the United States is growing. ICF walls have a high insulation R-value and significant thermal mass. An analysis was performed to determine whether the thermal mass tables in the Model Energy Code (MEC) fairly represent the performance of ICF walls and, if not, propose an alternative approach. Computer simulations using DOE2 and BLAST were performed to determine the relative performance of ICF and lightweight walls in a prototypical house in a range of climates. The BLAST results fall between the MEC integral and interior insulation position table values. The DOE2 results are consistent with the MEC interior insulation table. Analyses were also performed to determine cooling load factors for homes with ICF walls. These factors can be used in conjunction with Manual J procedures for designing air-conditioning systems in residences.