Roof Ventilation 101
I often get asked questions about the importance of venting an attic space or void between living space and a roof. I can’t stress enough how important it is to have good ventilation in your attic. The best vent systems however are not very effective unless they have somewhere to draw fresh air from (soffit ventilation) Here are several ways to do this in order of most effective to less.
1. Electric Power vent with thermostat: Having an electric power vent moves the most air of any other option. Depending on the size of your attic, and how much air you draw from your soffits, a power vent moves enough air to where you may not even need a ridge vent. Also, you have the peace of mind knowing that the temp. will never go past a certain point.
2. Ridge Vent in at roof peak: Here again, for air to want to move out the peak, it needs to be able to draw from somewhere, best case being a well vented over hang at the base of roof (soffits). It is important to make sure that attic insulation is not inhibiting the flow of air from these vents. Rafter baffles keep insulation from blocking the airflow. Remember that air does not fly out of there, and only a minimal amount of space can be cut out of the peak. A ridge cap is only 12 in wide, and the vent itself is about 10 inches, so only about 3 inches total can be cut out of the peak so that water cannot leak through.
3. Solar or Wind Turbine Vents: Both of these options depend on atmospheric conditions to operate (sun, and wind). However they have the advantages of not needing electric run to them, and are a little less to maintain.
4. Gable Vents: Gable vents are located at the gables of the roof, and work well when coupled with one of the other options. By themselves they do not transfer much air, but do work well with others.
It is a good idea to have one or more of each of these transferring air in the changes of seasons. I’ve often seen trapped air cause mildew, mold, and dry rot to the underneath of a roof deck. A well ventilated roof is the best way to ensure a long lasting healthy roof!