Q. I’m building a porch with a hip roof and a solid ceiling. Without soffit vents or roof vents will the roof get hot enough to shorten the life of the asphalt shingles? Are there any other reasons to vent a porch roof?
A. Bill Rose, architect and building researcher at the University of Illinois in Urbana-Champaign, responds: I would expect the overall performance of a vented porch roof and a porch roof without vents to be about the same. I advise you to look at porch roofs in your area to see what the local practice is, and to check with building code inspectors and follow their direction.
The joint where the top of the porch roof meets the wall needs to be flashed well, and most of the vent details for that look to me like they might leak water under some conditions of rain and wind. Soffit vents have much less risk of water entry.
People have strong and differing opinions on whether roof venting affects shingle life. Research on the topic has shown that venting will cool shingles by a bit, but no one really knows whether it will enhance the shingle service life, by how much, what the service life really is, or how it is quantified.
