And it can rather easily be added on the outside in some isolated ducts. The problem is cutting it down to appartments that correspond to fire safety codes. CAL

And it can rather easily be added on the outside in some isolated ducts. The problem is cutting it down to appartments that correspond to fire safety codes. CAL demands you have two exits, which a office building easily fullfills with two staircases. But how do you do that in a converted apartment building, without loosing tremnedous amounts of space to hallways.