On some houses, siding is nailed directly to the faces of the studs without any sheathing. With this type of construction, removal of the siding will result in an opening into the stud area which is too large for proper use of the sidewall nozzle. In such cases, use a length of lumber approximately 24 inches long and the appropriate width as a substitute for sheathing, drilling a hole in it for inserting the sidewall nozzle.