Looking for an effective nonpowered ventilator that isn't too noticeable? Ridge vents provide uniform cooling along the entire roof deck, installed from end to end on the roof with a low profile. There are two types of vents: metal ridge vents and shingle-over vents.
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A ridge vent is an important part of a home's roofing system. Installed at the peak of a sloped roof, the ridge vent allows damp, warm air to escape from the attic. A properly installed ridge vent increases energy efficiency and prolongs the life of your roof.
For a ridge vent to work properly, it must have adequate intake of fresh, cool air. As the ridge vent expels hot, humid air, intake vents feed fresh, cool air into the attic. Equal flow of exhaust and intake should be provided.
Example: 900-square-foot attic / 150 square feet = 6 square feet of net-free area.
Because nonpowered vents are rated by square inches, multiply 6 times 144 (the number of inches in a square foot). This gives you 864 square inches of net-free area. After calculating the net-free area, divide that number by 2 for equal amounts of intake and exhaust.
Using the example above, three round vents would be needed (432 / 144 = 3 vents) or nine square vents (432 / 50 = 8.64 or 9 vents).
Vents evenly spaced underneath the roof provide intake.
To calculate an example of exhaust and intake, use 25 feet of roof ridge vent. Multiply it by 18 square inches (the net-free air per foot of ridge). This gives you 450 square inches of total exhaust. Since exhaust and intake must be equal, 450 square inches of total intake is required as well. (25 feet x 18 square inches = 450 square inches)
Ridge vents come in panels or rolls. Instructions are given below for both plastic shingle-over and metal ridge vents.
If you are installing ridge vent panels, leave a 1/8 inch gap in between to allow for expansion.
Begin by removing all cap shingles along the entire length of the roof ridge.
Snap a chalk line along the center of the ridge peak.
Read your product instructions for cutting the correct size slots for your roof support system (roofs are constructed with or without a ridge board). Snap parallel lines on both sides of the peak, based on whether or not you roof has a ridge board. In general, measure 3/4 to 1 inch from the centerline if you do not have a ridge board, 7/8 to 1 3/4 inches if you do.
Mark the end of the slot 6 inches from the inside of each end wall.
With a utility knife, cut out the shingles within this marked area and remove the scrap. You're now ready to cut through the wood sheathing.
Set the power saw's blade depth to the thickness of the sheathing and any remaining shingles (about 3/4 inches to 1 inch). Create the slot by cutting through the sheathing along each chalk line on either side of the peak.
Remove the debris from the slot. You're now ready to install the ridge vents.
Do not cut through the roof trusses or ridge board. Make sure you adjust your saw blade depth properly.
Insert an end plug into the first section of ridge vent.
Center the vent using the alignment guides. For the best appearance, align the ridge vent end flush with the end of the house.
Pre-fasten the first section with 2-inch roofing nails through the pre-drilled sections.
Attach the remaining sections.
Using a utility knife, cut the last section to the proper length.
Insert an end plug and secure the final section. It should be flush with the end of the house.
Cut the cap shingles and nail into place using 2-inch roofing nails.
If you are using a nail gun, make sure you drive deep enough to attach to the roof deck but not so deeply that you dent or distort the ridge vent.
Follow the steps explained in Removing the Cap Shingles and Removing the Wood Sheathing.
Insert the end plug and connect the ridge vents with the connectors provided.
Cut the end of the vent to fit flush with the end of the ridge vent. Be sure to insert the end plug.
Align the joined ridge vent sections over the slot cut in the ridge peak.
Fasten them in place with 2-inch roofing nails.
Place straps over the joints, and fasten them into place with roofing nails.
Watch our DIY Basics video: How Do I Maintain My Roof?