i am insulating an exterior wall in my bathroom, and some of the stud spaces are less than 15 inches one is 9 the other by a corner is less than that. I have r-13 for walls 15 inches wide. Do i just cut it the long way, and risk not being able to staple it on one side. or do i just stuff the whole 15 inches into the 9 inch space. Or is there another batt like insulation less than 15 inches.