When a garage is attached to a house, a fire resistant wall is used between them, constructed with a 5/8 inch type X drywall on the garage side and a 1/2 inch regular drywall on the house side. The wall is built for the purpose of restricting or preventing the spread of fire between garage and house. A 2 hour fire rating requires two layers, and a three hour rating requires three layers of type X drywall.