Hey Jana -
It makes sense in most cases to exclude parking square footage from occupancy calcs, or use a very low default occupancy count.

USGBC has not defined 'basement' - I'm not sure about ASHRAE. I know that for us, it's the fact that the basement is a built, enclosed space that matters - the use of the space is not important the way our policies are currently written.

Hopefully this gives you a level of understanding that you need.