The door between the garage and the living area of a home is generally required to be a proper fire-rated door. Since many fires start in the garage area, having a pet door in the door to the house may allow a fire in the garage to spread more rapidly.
Inspectors will often refer to one-hour fire-rated doors. Most building departments consider a solid core wood door (not a hollow core wooden door) 1 and 3/8 inch thick, or a 1 and 3/8 inch thick honeycomb metal door, or a 20-minute fire-rated door as sufficient to meet this requirement. Once a doggy door or a glass window is put into the door, it loses its fire rating, unless the doggy door or glass is fire rated for this use. Most are not.
Fire-rated doors will sometimes have a metal plate on the hinge edge, indicating the door is fire rated. However, many doors that conform to the fire rating requirements do not have a plate or tag on the edge of the door. Another requirement of a fire door is that it be a self-closing door.
Leave or Replace
Many buyers are content with leaving the existing door, especially if they have a pet that would use the door. This is risky because many fires start in the garage. The safest thing to do is to replace a non-conforming door with a properly rated fire door.
The problem for many people is that they lose the pet door doing this. Should a buyer decide not to correct the problem, then at a minimum they should make sure that the garage has a heat detector and properly installed smoke and carbon monoxide detectors in the house.
Who to consult? Door hangers, finish carpenters, and qualified handymen.
DIY homeowners may install a fire door on their own. Door hangers finish carpenters and qualified handymen are the most proficient at installing and working on doors.