I am creating a LEED energy model for a historic building from the late 1800s. It has the typical load bearing masonry construction of the day. This includes limestone and brick walls ranging from 3'-8' thick. It has no insulation or air gap, which has created problems in accurately modeling the envelope performance. How can I properly model this and account for thermal mass? Since this is an existing building the envelope has to remain the same between the proposed and baseline and I am trying to get as accurate of a representation as I can.
I didn't find the right solution from the Internet.