Good attic ventilation lowers cooling bills, extends shingle life and reduces winter ice dams.
Is Your Roof Properly Vented?
Adequate roof ventilation reduces the cost of electricity needed to cool your home in the summer, extends your shingle life and protects the wood in your attic. Roof ventilation can be either active by using power vents, or passive by placing vents strategically using convection forces to rid the attic of the hotter air. They’ll protect your house from expensive future repairs. This article will help you determine if your attic is properly ventilated and show you how to install more vents if you need them.
Do You Need Better Ventilation?
How to determine whether you need better attic ventilation. In the summer, good attic ventilation reduces heat buildup in your attic and radiation of that heat into the living space below. That cuts cooling costs and prolongs shingle life.
In the winter months, warm, moist air seeps into the attic from the living space below. Good ventilation allows the moisture laden air to escape. That keeps your attic dry and reduces condensation.
Here are four signs of poor ventilation in an attic:
- Look at the eaves on your roof. What you want to see is a vent system that serves as an intake. This can be a vented soffit or louver vent in the soffit areas. It can also be a turtle vent lower down on the roof surface. If you don’t see any intake vents on the eaves or on the roof, your roof is not being vented properly. Also look at the ridge line of your roof. What you want to see here is an exhaust vent. This could be either a ridge vent or turtle vents in the case of passive systems, or power vents in the case of active vents. Bear in mind your roof vents may not look anything like the ones shown in this article. Gable vents are not factored into any attic ventilation calculations. Having intake vents and exhaust vents allows for the warmer air to rise and leave the attic. The upward movement of air dramatically reduces the radiation of warm air into the living space below.
- Touch your ceiling on a warm, sunny day. A hot ceiling tells you that the attic is acting like a solar oven, raising your cooling bills and warming the shingles.
- Thick ridges of ice on your eaves in winter are a sign of poor attic insulation. Warm air that escapes rooms below gets trapped in the attic. Snow melts and the water refreezes on the cold eaves, creating ice dams. Are you the house in the neighborhood with the snow melting off first?
- Warm air that escapes living space also carries moisture that will condense on rafters or roof sheathing. Grab a flashlight and inspect your attic during the winter. If you see dampness or frost, you need better ventilation in your attic.
For the best results, place roof venting near the roof’s peak and soffit vents in the eaves. Air flows in through the soffit vents and out through the roof vents. Vents come in various styles. We chose rectangular, hooded roofing vents and rectangular soffit vents because they’re easy to install. Everything you need is available at home centers. Aside from vents, you’ll need a handful of 1-1/4 in. roofing nails, 1/2-in. galvanized screws for the soffit vents, utility knife blades, a dust mask and one tube of roofing cement for every three vents. You’ll cut holes for the vents with a jigsaw or reciprocating saw. Expect to spend a full day on this project. A cool day is best. On a warm day, attics can get dangerously hot. Heat also makes shingles easy to damage.
How many vents do you need? First determine your roof area by multiplying the length by the width. A 30 x 40-ft. roof, for example, has an area of 1,200 sq. ft. Then aim for about 1 sq. ft. (144 sq. in.) of vent opening per 150 sq. ft. of attic. Be sure to have your soffit or eave vents be the same size as your attic vents. This enables the best flow of cooler air from the outside into your eaves when the warmer air is leaving along the ridge line.
How to Install Roof Vents
Mark vent locations
Center nails between rafters 18 in. from the roof’s peak. Drive nails up through the sheathing and shingles to mark vent locations.
Cut the shingles for roof vents
Cut shingles with a utility knife. Make the cutout area 1/2 in. larger than the vent opening. Chalk provides an easy-to-see cutting line.
Cut the hole for roof vents
Cut a hole in the roof sheathing with a jigsaw or reciprocating saw. Drill a starter hole so you can insert the blade to begin the cut.
Remove any obstructions
Slip a pry bar between the shingles and separate the self-sealing adhesive. Then remove any shingle nails that prevent the vent from sliding into place.
Place the vent
Slide the vent into place. Nail the lower edge with roofing nails.
Install the vent
Apply roof cement where shingles meet the vent. Add a dab of cement to secure the shingles to the vent base.
Please note that even though we provide instruction on how to install vents, we recommend having a licensed roofing contractor install the vents on your roof. Circumstances on roofs differ widely and one method shown here may not be the best installation method for your roof.