My stairs leading from one floor to another are over a room in the garage that houses the water heater. I think I would benefit from insulation the bottom of the stairs. From what I can see, I'm thinking about buying the 4'x8' sheets of foam board and cutting them and putting them on the underneath side of the stairs. What do you folks think of this idea? Got a better plan? And what type of glue would you use on the polystyrene foam to hold it to the wood?