C4 for housing would be: * Have a high level blueprint of the house for typical humans. * Have a detailed blueprint of the house for contractors. * Have a ci

C4 for housing would be: * Have a high level blueprint of the house for typical humans. * Have a detailed blueprint of the house for contractors. * Have a circuit diagram for the utility systems like electricity * (Optional) Have a detailed specification for every plug and fixture etc. Basically, have a diagram for every level that will be notably unique or useful to have for the system. If you need a code level diagram, either you're doing some complicated custom work or most likely over specifying the design that can be left as an implementation detail.