Mass Floor Insulation:
The mass floor insulation should not exceed the current requirements in 90.1-2007 for CZ 5-8, except CZ 5 nonres can be increased to R-12.5ci and CZ 7 nonres can be increased to R-15ci. These are at least as great as NBI Core Performance (R-10ci in CZ 5-6 and R-15ci in CZ 7-8); AEDG small office (R-10.4ci in CZ 5-6 and R-12.5ci in CZ 7, and R-16.7ci in CZ 8); and AEDG retail (R-12.5ci in CZ 5-6 and R-14.6ci in CZ 7-8).
The insulation for mass floors was increased without considering how mass floors are actually constructed and insulated. The current method of determining cost effectiveness within 90.1 is outdated and does not consider interactions between energy measures. Even so, the Jan. 5 version optimization spreadsheet had the correct measures for insulating mass floors. During the January meeting, additional measures were hastily added without full envelope subcommittee discussion and without consulting architects and designers who actually insulate mass floors. See the attachment for an illustration of how a moderate amount of insulation can actually improve performance by improving compliance.
In addition, the mass floor equations from Appendix C, Table 6.10.2, do not reflect the performance of mass floors. These are outdated equations that are probably based on walls. Note that the cooling coefficients for mass floors are higher than those for frame walls, which does not make sense because the floors do not see solar effects and will have the benefit of mass.