If the school says you are at least a half-time student, room and board expenses even while living at home as a commuter student are 529 qualified expenses, up to the published COA numbers as provided by the school. The only reasonable number is the number that the school can give you for your current living arrangement. If you use grant money to pay room and board expenses, it will be taxable income to you. Room and board is a 529 qualified expense (as long as the school considers you at least a half-time student), but it is never a qualified expense to keep grants and scholarships tax-free.