Repair & Maintenance

Proper attic ventilation is important

By David Pettebone
Info Guru,

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Do your research before you purchase an attic fan
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Consider the ways to achieve proper attic ventilation

Most people immediately think about an attic fan when considering how to achieve proper attic ventilation; however, that might not be the best solution. According to. Dwight Barnett(, a certified master inspector who contributes articles to HGTV, you should not use a vent fan, canned vents or turbine vents with a ridge vent. "The ridge vent is designed to promote airflow from the soffit vents. Because air is leaving the attic space, outside air needs to enter in to replace it. This "make-up" air enters each soffit vent, where the make-up air absorbs heat from the attic, rises to the ridge vent and, voila, you have free thermal attic ventilation."

Mr. Barnett writes that if you install a roof/attic fan and the home has a ridge vent, the fan would pull air through that portion of the ridge vent closest to the fan. Therefore, the soffit areas below the fan and the ends of the attic with gable vents would have little or no airflow. Remember, when thinking about proper attic ventilation, in winter, cool, dry air enters the soffit vents, absorbs warm moisture from the attic and vents through the ridge vent. An attic fan that has a thermostat would not be working in cooler temperatures, and all the moist attic air would remain to be a source for mold and decay. The proper use of a ridge vent system is to have soffit, or overhang, vents that allow outside air to enter freely, flow up through each rafter space and then out through the ridge vent. Soffit venting needs to be equal to the ridge vent in the amount of airflow that passes through.

However, if you do not have ridge vents on your roof, and do have properly installed soffits, you should consider an attic fan to achieve proper attic ventilation. Mr. Barnett writes, "The temperature of the fan should be set around 90 degrees. However, the major concern in an attic is moisture, not heat. The attic is normally separated from the home by insulation to protect the living areas from the hot or cold air trapped in the attic. If moisture is present in the air (and it is), the insulation, roof decking and roof covering can be damaged. It is most important to have a humidistat installed on the attic fan to vent the moisture. Set it to 40 percent humidity and let it run. An attic vent fan should operate in winter as well as summer."

Along with proper attic ventilation it is important to make sure the attic floor is well-insulated to avoid thermal airflow coming from the home's living areas and not from the soffit vents. Conditioned air from the home will exit through the ceiling and out through the ridge vent or an attic fan's opening, thus wasting energy without proper attic floor insulation.

If you are building a new house, remodeling your current residence or are having a new roof installed, be sure to talk to your contractor about the many ways you can achieve proper attic ventilation. Do your homework by going online and visiting the many sites that offer advice as well as products—particularly if you are among the growing list of do-it-yourselfers!

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