Here it is based on heated space. If it is unheated then it is not habitable.
I had a job where a lady owned family land that had her dad's old hunting lodge out in the middle of the woods, a small 2 room block building with a porch. She wanted to put a bathroom in it so she could use it. She hired a GC, pulled full permits, drilled a well, put in a septic system, put in a full bathroom, water heater and full kitchen. She even added a bedroom. I wired it fully to code except the 12' rule. It even had phone and cable.
The inspector tried to fail it but had to pass it under duress after arguing with the GC. The only heat was a wood stove and a small space heater in the bathroom, therefore it was "uninhabitable".
