The 4 Inch Vent Misconception

There is often confusion about the 4 inch vent. The probllem lies in that roofers often refer to a 3 inch vent with a 4 inch flashing as a 4 inch vent. This is problematic for us, because to us a 4 inch vent is an actual 4 inch vent with a 5 inch flashing and would use a custom M size unit. So when a roofer tells you that you have a 4 inch vent, please confirm if its a 4 inch flashing or a 5 inch flashing. If its a 4 inch flashing on a 3 inch vent, thats a standard Size B unit.