I have a 2 story solid brick house, 3 wythe (3 brick thick), with plaster directly on brick on the interior. Heat loss and gain through the walls is significant once they either heat up in the summer or cool down in the winter just due to the thermal mass. HVAC-Calc shows a drop from 160k BTU to 95k BTU heating and from 7 tons to 4.5 tons cooling with insulating the walls (160k and 7 tons is with everything sealed up and the attic already insulated) I was planning on building out a metal stud 2x4 wall on the inside of the brick walls leaving 1/2" gap between the studs and the brick then spray foaming the whole thing including the 1/2" gap with open cell foam. Metal studs because my ceilings are 10' and straight 2x4 of that length are hard to find and open cell foam vs closed cell because open cell is vapor permeable so it would not trap moisture in the wall. The foam directly on brick would not allow a cold surface for condensation to happen, a problem with batt or cellulose insulation. Thoughts/opinions? Am I better off leaving well enough alone for the sake of the brick? It is the old soft brick with lime mortar that is sensitive to moisture and freezing.