The witches hat vent has a seamless top, preventing water and snow entry. The internal louvers prevent insects, rodents or birds from entering. The witches hat ventilates the attic by letting out hot air in the summer and moisture in the winter, and is ideal for flat or low sloped roofs. The detachable head allows for easy installation on EPDM, PVC, TPO and other roof membranes. Constructed of heavy gauge, rust free aluminum.
The diameter size of all roof vents determines the Net Free Area, also known as the "NFA". NFA is the measured amount of opening each vent offers at each specific size. to be available for venting air through a specific vent size. The calculator below will find the overall number of vents needed to effectively ventilate the targeted attic space.
Once you have the area, the numbers shown below are the number of vents of that size which would ventilate the specified area with both 1/300 and 1/150 rule.
The roof vent calculation values shown above are for the exhaust portion of the roof. The same amount of net free air inches is needed for air intake as well. Proper roof ventilation consists of 50% air exhaust and 50% air intake.