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?
Thanks,
—Fred W., Pinckney MI
Hi Fred,
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 kpaul@handypro.com.
Comments
Keith A. Paul
Mon, Apr 15, 2013 : 12:11 p.m.
Hi Mike, I'm glad to hear there is no moisture problem, as you can tell. Your solution mostly depends on the details of your home. Because heat rises, proper ventilation and insulation is key to help avoid ice damning and extreme heat during the hot summers. Roofing should have a soffit vent so that air can move freely from the bottom to the top of the roof, (even if you don't have a soffit, there are retro-fit systems that can be installed behind your gutter http://www.dciproducts.com/html/fasciavent.htm). Baffles can be installed. Another option to help is an automatic roof vent fan, to help regulate the heat. http://www.gaf.com/Roofing/Residential/Products/Roof_Vents/MasterFlow_Power_Roof_Ventilator Again, proper insulation and ventilation are key to an attic living space, you may want to consider a window are conditioning if you don't have central air for those extremely hot moths.
Mike
Fri, Apr 12, 2013 : 5:20 p.m.
My house has gable end venting, no soffit vents and a finished room in the attic. There is insulation in the triangle attic space behind the knee wall, ceiling rafters and roof rafters to the top of the finished room ceiling. The only ventilation I can see is that above the ceiling, about 4' x 30'x 2' again with gable vents at both ends. I do have a problem with ice backup on the roof. There doesn't seem to be any moisture problems or rotting in the attic triangle area. However, the finished area is very hot in the summer and cold in the winter. There is no room to put in soffit venting. Any suggestions?