Venting a roof is a two-prong process or system. Roof ventilation involves pulling cool air in through intake vents and drawing warm out through exhaust vents. This is called “air exchange” and is the key to keeping excessive moisture from building up, causing condensation. If the system is not properly sized and balanced, it will become evident in the following ways: extreme heat in the summer; compressed or wet attic insulation; or water stains on the ceilings. Inadequate ventilation may also lead to problems with fungus, mildew or mold. Also, excessive moisture can lead to structural members rotting and becoming unsound.
The vents must be large enough to provide adequate ventilation. Most local building codes have a minimum requirement of one square foot of attic ventilation for every 150 square feet of attic space. The minimum requirement may be increased based on the pitch of the roof on the building. Discuss your project with the building inspector to find out what the codes are and the best way to vent a roof in the climate where you reside.
Choose from ridge vents or power vents for exhaust vents. Keep in mind that what is important is balance and capacity. Install 50 percent intake and 50 percent exhaust vents to move the air. The rule of thumb for attaining this balance is to measure the length of the ridge vent and double the number to get the total length for your intake vents. If you are installing roof power vents, take the cubic feet per minute, or the CFM, and divide it by 300 for the proper number of intake vents to install.
The best type of exhaust vent may come down to a matter of personal preference. Ridge vents have a clean, and not so obvious, appearance, although the roof is vented from end-to-end.The roofing shingles installed over the top of ridge vents help conceal the vents. Install a series of vents along the peak or one continuous vent.
Power vents are more noticeable but can move larger amounts of air faster. Powered exhaust vents include wind turbine, solar power or electric power vents. Solar and electric-powered vents can be installed on the roof or in the gables. Roof vents that operate on electricity use thermostats and humidistats that power on or off based on the reading of these two controls.
Wind turbines extend about 20 inches above the roof line and have a shiny dome attached at the top. If you live in an area that receives regular gusts of wind of at least fvie miles per hour, wind turbines may be the best choice. These roof vents allow air to flow out even if the wind isn’t adequate for operating the turbines.
Intake vents are pretty standard and are available in various dimensions. Install intake vents on the lower walls or the soffits of the attic.