I think you left something out of the post. Is your garage 2 -1/2 inches, feet, meters, or something else from the house? What exactly do you mean by attaching the garage to the house, do you want to make the house exterior wall the exterior wall for the garage as well? Do you want a door between the house and the garage? Connecting a house and a garage usually requires fire rated walls and a fire rated door, plus a minimum elevation difference between the garage floor and the house floor so spilled gasoline will not flow from the garage into the house. Your building inspector would be a good place to start to discuss the issues and how best to meet them.