Roof Ventilation in Sterling Heights, MI

A ridge vent is a slot cut along both sides of the peak and covered by a low baffled vent strip, with cap shingles nailed over it so it disappears from the street. It sits as high as an exhaust can, which is where the code wants its upper vents: within 3 feet of the ridge. A 1979 University of Minnesota extension sheet on ice dams found continuous soffit-and-ridge venting worked better than individual soffit vents, roof louvers or power vents. It only works with enough intake below it.

Static louvers, also called box vents or "turtle" vents, are square hoods set over holes cut in the deck near the top of the slope. They have no moving parts. Each one adds a fixed amount of net free area, so a long attic needs a row of them. HomeGuide lists static roof or gable vents at $200 to $700 installed. Louvers fit hip roofs, which have little ridge length, and short ridges broken up by dormers. Their flashing is the weak point. The upper flange has to slide under the shingle course above, not sit on top of it.

Turbines, or "whirlybirds," are wind-driven vanes over a round throat. On a calm day a turbine is simply an open hole with a cap on it. HomeGuide prices a roof turbine at $150 to $300 installed, the cheapest exhaust on its list. Old ones with worn bearings stop spinning, and a turbine sitting on a roof that also has a ridge vent becomes the second exhaust type Air Vent warns about. If a reroof adds a ridge vent, the turbines should come out and the holes should be decked over.

Powered fans push air out on a thermostat or humidistat. HomeGuide lists electric roof fans at $200 to $1,200 installed and solar ones at $300 to $1,400. Most fans come with a thermostat or humidistat, and adding one runs $100 to $300. Energy Vanguard, a building-science firm, explains that a power attic ventilator pulls part of its air out of the house through ceiling leaks, so it ends up cooling the attic with conditioned air, and in real houses it has backdrafted water heaters and put carbon monoxide indoors. HomeGuide notes most pros don't recommend electric fans. In our view, a fan makes sense only over a well-sealed ceiling and never alongside a ridge vent.

Intake is the half people forget, and without it the exhaust has nothing to pull. Air comes in through perforated vinyl or aluminum soffit panels or through individual soffit vents (HomeGuide: $15 to $30 each, or $2.50 to $4.00 a foot for continuous strip). The code wants at least 1 inch of clear space between the insulation and the roof sheathing at the vent, and it bars blocking or insulation that stops the airflow. Foam or cardboard rafter baffles hold that channel open, so a later round of blown-in insulation doesn't bury the soffits. Vent openings must be between 1/16 and 1/4 inch, or screened to that size, to keep out birds, wasps and snow.

Gable vents are louvered openings in the end walls just under the peak, common on older ranches and split-levels. Air Vent counts gable louvers as their own exhaust group, so a house with gable vents and a new ridge vent has two exhaust types fighting each other. Following that rule, a ridge vent retrofit means closing the gable vents off from the attic side, and the louver can stay on the wall for looks. HomeGuide adds that when a gable fan is mounted, any part of the gable opening the fan doesn't cover should be sealed.