Ridge or Gable Vent

Catherine from California is asking the following: We are looking to get our roof replaced. One roofers said we have to add ridge vents and O'hagin vents to ensure we follow warranty specs. As of right now there are only gable vents and a fan for outflow in one South facing gable. Temp range in this location is 29' low at winter and occasionally 110' summer. Is this accurate advice?

Below is what our roofing expert Marty Stout from Go Roof Tune Up had to say in response to your question:

Current codes and manufactures require ventilation at a ratio of 1 to 300 or 1 to 150 depending on local requirements. This means one square inch of ventilation for every 300 or 150 square inch of attic space. Many houses that are ready for reroof don't have the necessary ratio and need to have ventilation added.  This ventilation must be 50% low on the roof line (intake) and 50% high on the roof line (Exhaust). Cooler air goes in low, warmer air goes out high. Ridge vent and O'Hagin's are a good way to achieve this goal.