Understanding Attic Ventilation

Q: I’ve had five different contractors bid on a reshingling job, and I got five different recommendations on details. One of the discrepancies has to do with attic vents. Some say a ridge vent will provide enough air movement in my situation, some say it won’t. I’d prefer not to use those rooftop mushroom vents if possible. What’s the formula for figuring out the amount of vent area needed?

A: Yes, ridge vents are much more visually appealing because they’re almost invisible. All you see is a slightly raised section of shingles along the peak of the roof. According to the building code, minimum attic vent area must be at least 1/300 of the floor area of the attic itself. That's a minimum, mind you, and it's always good to go beyond this figure if you can. Start by calculating the area of the proposed ridge vent, then decide from there. But while you do that, ask yourself if you've had problems associated with inadequate attic ventilation. This would include shorter-than-expected shingle life (caused by an overheated roof surface in summer), and frost build-up inside the attic during winter. If you don't have these problems, then adding abundant vent area probably isn't necessary. I dislike the appearance of rooftop mushroom vents too, so if you can avoid them, that’s an excellent plan. The good news is that you can go with a ridge vent right now, then easily add more vents later if needed.