To gable vent or not to gable vent
Photo by Nicholas Paul
This question came from the comments for my recent Extend the life or your roof with proper ventilation article:
I had a roof replaced last summer and had similar differing opinions on ventilation, My attic is not finished. The underside of the roof deck is not insulated and is visible and exposed. All the insulation is between the ceiling joists.
I have open soffit vents for the entire length of the soffits, ridge vents along the entire length of the ridge, and three large gable vents. I was told by two roofers that the gable vents are not needed and are actually resulting in not enough air flow through the soffits.
All these vents were installed 25 years ago, and, since that time, there has been no visible moisture problems such as ice dams or condensation. When this second roof was installed last summer, there was no need to replace any plywood. Only the shingles were badly deteriorated.
If I closed the gable vents, would that help get better air flow during the summer months, and possibly help keep the underside of the shingles a bit cooler, and maybe even prolong their life a bit more?
Are my gable vents a problem, and should I close them?
—Fred W., Pinckney MI
A properly vented attic follows the simple law of nature — heat rises. But due to the complexity of this law within a residential attic, organizations and research firms have been investigating this issue for many years.
I'm glad to hear that you've had little issue with your roof. Most improperly vented roofs can cause major problems. The attic can reach up to 60 degrees higher than outside summer temperatures, causing the shingles to prematurely deteriorate and can contribute to ice damming during the winter months.
In the 1930s, insulation started to become commonly used to primarily keep moister out of the attic. It wasn't until the 1940s that subsequent building codes and the American Society of Heating Refrigerating and Air-Conditioning Engineers (ASHRAE), standards were put into place to regulate insulation and attic venting practices.
Because of upgraded building products and methods, further research was needed to correctly identify proper ventilation techniques and uphold the two fundamental principles of a well ventilated roof — keep the heat and moisture out. This can be accomplished by maintaining the same approximate temperature and dew point as the outside air.
The fundamental principle of a ridge vent is to ventilate a constant and even air flow from the soffit vents across the underside of the roof then exiting through it. Many roofing contractors discourage using a gable vent with ridge vent and soffit vents because a gable vent interrupts the proper airflow and can cause the air current to flow perpendicular and unevenly throughout the attic.
This can eliminate the pull of air through the soffits to the ridge, thus not properly moving enough air or the direction of it. And that can cause premature deterioration to your shingles and allow moisture into your attic.
According to Adam Helfman, home improvement expert and radio show host, most gable vents installed now-a-days are used for aesthetics rather than venting because of the gable vent inefficiencies.
Why else are gable vents undesirable with ridge vents? According to a report prepared for New York State Energy research and Development Authority conducted by Synertech Systems Corp. in 1993, not only do gable vents largely depend on the wind direction and but have been reported to create suction bringing snow into the attic.
Therefore, back to the first paragraph, heat rises, which means the air entering the soffit vents then exiting the ridge vents are the best solution for many normal roofing structures.
Handyman Tip: I’ve heard of ridge vents getting clogged with blown in insulation. Be sure to keep them clean for proper air flow.
Again, I’m glad to hear that you haven't had any issues with your existing roof; however, from my research, your best bet is to cover the gable vents to ensure proper airflow and moisture control.
Paul is a State of Michigan Licensed Builder. Paul serves as President and founding member of Nationally franchised HandyPro Handyman Service, servicing Washtenaw, Wayne and Oakland Counties. www.handypro.com. Listen to Paul every Saturday at 11 a.m. on “It’s Your Business, Make It Happen” WAAM Talk 1600AM. Email questions or comments to firstname.lastname@example.org.