There are many factors for converting a garage, but the most common is the fact that you must have in most cases, covered two car parking, i.e. garage or carport. If there are utilities in the garage such as laundry, water heater or furnace it may be an issue for safe conversion due to venting combustion air etc. As far as adding an exterior addition, the most common restriction is the setbacks from the side and rear property lines. It is absolutely essential that you involve the building department, not only because it is the law, but also for you own safety and the fact that if you ever sell the home you want to be in compliance.
Rory Hernandez, owner
ASHI Certified Inspector #244418