I'm looking to finish insulating my garage. it is attached to the house so one wall is already insulated. it has covered walls that are drywalled. My question is, would I be ok to insulate the side walls and the wall that the roll-up door is on and not insulate my ceiling, or would it be recommended to do the ceiling? I store my Genesis in the winter and dont drive it so I was thinking insulating the garage would be good for the car when it gets cold out. There is no heating or cooling going to it right now. I probably would do some type of spray in insulation so I dont have to remove the drywall completely.