Roof Ventilation Tips

LESLIE: James in Texas is calling in with a roofing question. What can we do for you?

JAMES: Hello, I’ve got two houses I’m planning on putting a – thinking about putting a new roof on. The first house is a 600-square-foot with a gable roof and it has no vent in the overhang but on the north and the south sides there are louvered vents; it measures 12×18 inches. I was wanting to know is this sufficient for ventilation in the attic?

TOM: OK, James, you say that you have soffits; you have the overhang but there’s no vents in them?

JAMES: Right.

TOM: OK, the best type of ventilation system, James, is one where you have continuous soffit vents and a continuous ridge vent. The vents in the gable are not that efficient; although certainly roofs were vented that way for many, many years. But we know now that the best ventilation system is when you have vents in the soffit and vents in the ridge and here’s why: because as air blows over that roof, it tends to depressurize the ridge vent that draws out the hot air in the summer, the moist air in the winter and the wind also blows against the soffits and pushes it in. So, basically, you have a positive pressure at the soffit that pushes air under the roof sheathing, goes up under the sheathing and exits at the ridge; so, basically, it’s a 24/7 system that does a really good job of efficiently taking the heat and the moisture out of your attic. Gable vents by themselves, not so much.

JAMES: OK. I’ve got another house that is 1,000 square feet with a hip roof and has a – oh, I guess about a 10-foot ridge vent with vents in the overhang and there’s also a motorized power vent. You know power vents don’t have a tendency to last very long.

TOM: No, they don’t and what happens – especially if that attic fan, is what I think you’re talking about, if that is near the ridge vent, what’s going to happen is it’ll actually depressurize the ridge vent so it’ll suck in outside air, take it through the attic and push it right back out again. It’s kind of like a dog chasing its tail.