I've reviewed the ANSI standard in some detail, it’s really a GREAT resource and quite comprehensive. It seems like there might be some potential area's not covered for example; 1) A 25 X 40 home with a nominal 2x2 (H20 heater) area with outside only access through small door. Typically these area's are reported as sq/ft. (it’s just a gray area) 2) Similar utility areas that are within the 'footprint' of the home, however that are larger say 4 X 6, also with no internal access but within the footprint of the home (concrete foundation) 3) Utility areas within the 'footprint' of the home but with garage only access to the area through utility doors. There are others, however they are harder to explain... and have to do with custom homes with design touches & 'non useful' but good looking touches to what is normally the front or street elevation. Is there a more comprehensive explanation of these standards, or an alternative standard?