Tuck under garages allow a homeowner to have the convenience of a garage built into the home, rather than separated into a different building. But because it is part of the home's body, the finishing touches of the garage are different than a typical garage built off the side of a home.
Because many people, especially in colder climates, run their vehicles in the garage to warm up, there should be a firewall within the garage to prevent any possibility of a garage fire spreading. Also, the garage's ceiling should be insulated densely with cellulose. This will prevent fumes from reaching the above living area and help keep energy losses to a minimum.
If a tuck under garage is properly finished, the entire room will be self-contained from the rest of the house. Make sure to patch any wall or corner holes to keep fumes from spreading.