Q&A: Venting Hip Roofs

A.Builder Mike Guertin responds: The short answer is yes. I know that venting hip roofs adequately can be difficult, and that many people think that the relatively unobtrusive ridge vents are a better aesthetic option than a bunch of unsightly mushroom vents.

However, I’m not a fan of using ridge vents along hips. I installed ridge vents on the hips of two homes 11 years ago. About six months after the homes were complete, both homeowners had water stains on the second floor ceilings. I found the fiberglass insulation damp beneath a couple of the hips, and I could see where water had dripped along the hip rafters. I thought the leaks were due to a particularly severe thunderstorm and figured it wouldn’t happen again. But two weeks later, during a moderate storm, the leaks recurred. I removed the hip vents and haven’t had a problem since.

My present roof venting strategy is to use a continuous soffit vent (either a strip vent or a fully vented vinyl soffit), and to use a ridge vent on all true ridges. (I haven’t had any callbacks from leaking ridge vents installed on actual ridges.) Some ridge vents work better than others. I think ShingleVent II by Air Vent is better than many of the others. I’ve found some of the roll type vents subject to installer errors that reduce the net free vent area.

On a hip roof that lacks enough of a ridge for adequate venting, I install roof vents (mushroom vents) cut high on the roof slopes that aren’t likely to be viewed.

One of the reasons for installing attic venting is to remove moisture vapor that can condense on roof framing, potentially causing rot in cold climates. If you stop moisture from getting into the attic in the first place by tightening up the ceiling, you can reduce the need for attic venting. Moisture " piggybacks" on the air that leaks into the attic. The biggest air leaks you’ll find are at attic access panels or pull-down stairs, standard recessed light cans, regular light fixture electric boxes, hvac ducts and chases, whole-house fans, and the spaces around pipes and wires that run through the top plates of walls. During new construction, these air leaks are easy to address.