Durovent 22" x 48" Rafter Vent, Constructed From Extruded Polystyrene Foam, Net Free Air Is 18.7 SQIN, Extra Wide Nailing Flange 1.5" Makes It Easy To Install, Full 48" Long, The Minimum Length Needed To Guarantee Airflow Through The Insulation, The Vent Is Pizza Cut In The Middle, Making It Easy To Split 2 For 16" On Center Applications.