So I am having a trouble insulating my old condo from the 1950's without any 2x4 wood frame. When I opened the walls, it had brick, plasterboard and drywall on top. There was 1/2 inch wood separating them all. I'm in a pickle. I really do not know how I should insulate the walls that do not have the 2x4 wooden frame fit for insulation. Should I take out all the plasterboard and create a whole new frame fit for insulation? or is there a way for me to leave the plasterboard and put on foam board insulation on top of the plasterboard? Also when I put my hand inside the brick area, there is air flow. Should patch those up or is that air flow needed? Renovation is hard during Covid, please any tips?