Ridge Vents on Low-Slope Roofs

Q: I plan to reroof my early-'60s ranch house and am concerned about ventilation. The house now has three gable vents, with soffit vents in every rafter bay front and back. When I reroof, I want to add a ridge vent, but my roof only has a 4:12 slope. Will that be a problem?

—John, Toledo, Ohio

A: Tom Silva replies: Ridge vents are great, but I'd avoid them in this case. Your roof has a fairly low pitch, and snow (or rain) could blow into the attic through the vent. So unless you've noticed signs of ventilation problems, such as ice damming in the winter or roof shingles bubbling and curling from overheating in the summer, I think you should stay with your existing arrangement.

By the way, 4:12 is about the minimum slope suitable for asphalt or fiberglass shingles. To improve the weather protection, I'd reduce the maximum exposure of the shingles from 5 to 4½ inches, and I'd use six nails per shingle instead of the standard four.
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