Create a cleaner, more weather-conscious mounting base for a compatible universal dormer vent with this 7.5-inch by 19-inch sub-base flashing. The formed metal accessory includes 3-inch flanges on all four sides to support integration with the surrounding roof assembly and uses an 8-inch by 20-inch cutout. It is intended to complement the matching dormer vent and should not be presented as a standalone fire- or ember-resistant vent. Confirm compatibility, roof pitch, finish, flashing sequence and waterproofing requirements before purchase. The broad flanges should be protected with rigid packaging so they arrive flat and ready for installation.