It seems everyone knows that the door leading to an attached garage from the residence needs to be at least a one hour burn through fire rated door. A hollow core non fire rated interior type door to the garage is not an option. (below a picture of a common hollow core door)
It seems that during my inspections, I find that in many homes one small but extremely important device is overlooked. This door must have a device or hinge that automatically closes the door to the garage. Not only in the case of a fire but in those cold times when, in a poorly insulated garage especially, you may need to warm the car up for a period of time. As you go back in the house for a cup of coffee, or whatever, the fumes from the car are allowed to enter the home, without such a device. Carbon monoxide from your vehicle can enter the home and it is very harmful to your health. Even if your area has no "building codes" that requires this device, your health and safety depend on it! Please, automatically shut the door!