What is the maximum width for cutting ridge vent slots?

Follow the installation instructions for cutting the slot size.

Follow the installation instructions for cutting the slot size. For Air Vent ridge vents the slot size is  impacted by the roof construction. Specifically whether or not a ridge pole is present. Consult the installation instructions for more details. Here are some common mistakes regarding slot width: too wide, too narrow, and one side only. Slots cut too close to the louvers of the vent could lead to weather infiltration. Bottom line on slot width: The slot should be no wider than that which leaves 2" of deck under the vent on each side of the slot starting from the top of the vent (that is, the slot-side top of the louvers on the vent). If the slot width leaves less than that amount of deck it is potentially problematic. Slots not cut properly on one side forces the airflow to divert to the other side. This is not ideal.