My contractor is not going to drywall portion of kitchen ceiling as it will be covered by 9" cabinet crown molding. There are mechanicals (water supply lines, HVAC, and drain pipes) in the way. The area behind is unfinished dead space around a curved staircase. I worry about mice getting into kitchen as I have a wooded backyard. I also wonder if there is some type of fire barrier safety issue. Is this a good solution? Is this acceptable and compliant?