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Improve Your Attic Ventilation with Soffit Vents

Here’s how to install soffit vents step by step to improve the airflow in your attic.

False-front Gable Roof Nancy Andrews

If you’re looking to install new ventilation in your house, you might want to consider a soffit vent.

Should I Add Soffit Vents?

If your home is fitted solely with small gable-end vents or a ventilator high in the roof, you might want to consider adding soffit vents to increase airflow. These vents allow outside air to enter the attic at the lowest point of the roof—along the underside of the eave. They’re most effective when used in conjunction with a continuous ridge vent.

Soffit vents come in several sizes and styles, including small round discs and rectangular grilles. We opted for aluminum strip vents that measure 3 in. wide x 8 ft. long. This style vent provides a quick way to ventilate every rafter bay. Strips vents come in white, brown and silver; you’ll pay less than $3 for an 8-ft. length.

How to Install Soffit Vents

Step 1

Make Two Parallel Lines

Person marking ceiling to prepare for soffit vent installation.

Start by using a chalk reel to snap two parallel lines down the center of the soffit. Space the lines 2 in. apart; that will allow the vent to overlap the cutout by ½ in. on each edge.

Step 2

Cut Parallel Lines

Person cutting a soffit vent with a circular saw. Photo by Merle Henkenius

Next, bore a 3⁄4- or 1-in.-dia. hole through the soffit right between the lines and measure the thickness of the soffit panel (probably 1⁄4 or 3⁄8 in.). Then set your circular saw to that depth and cut along the chalk lines.

Cut the two parallel lines with a portable circular saw. Set the blade depth to barely cut through the thin soffit material.

Step 3

Connect the Two Cuts

Person using a hammer and chisel on the ceiling. Photo by Merle Henkenius

When you near the end of the soffit, stop short and connect the two cuts with a sharp chisel or sabre saw. Once all cuts are made, use a thin pry bar to remove the 2-in. plywood strip. Pull any nails that remain in the soffit framing with a cat's paw.

Then inspect the length of the vent cutout. If there's any insulation clogging the slot, pull it out or shove it back up.

Step 4

Raise the Vent up to the Soffit

Person raising a vent to improve attic ventilation. Photo by Merle Henkenius

Next, lay the strip vent down on a flat wood surface, such as a plywood sheet or long 2 x 4, and drill 1⁄8-in.-dia. screw holes through both flanges. Space the holes 12 to 14 in. apart. With the help of an assistant, raise the vent up to the soffit and center it over the cutout slot.

Step 5

Attach the Vent to the Soffit

Person using a drill to install a soffit vent. Photo by Merle Henkenius

Use a cordless drill/driver to secure the vent to the soffit with ½-in.-long No. 4 sheet-metal screws. Continue installing additional strip vents until you reach the far end. Trim the last vent to length using aviation snips.

Step 6

Remove Any Insulation From the New Vent

Person checking attic insulation. Photo by Merle Henkenius

The soffit vents are now installed, but you still need to make sure there's no insulation blocking the new vents. If the attic is insulated with fiberglass batts, just pull back any that are blocking the flow of air. If there's blown-in insulation, like ours, rake back the fluffy stuff with a 3- or 4-ft.-long 1 x 6, or use a garden rake or hoe.

Step 7

Install the Ventilation Baffle

Person stapling a ventilation baffle to wall. Photo by Merle Henkenius

Finally, to ensure that the airway to the vent remains open, staple a ventilation baffle to the plywood sheathing in each rafter bay. The molded polystyrene baffles, available at home centers and lumberyards for about $1 each, form channels that hold insulation at bay and direct incoming air upward.

Can You Have Too Much Ventilation in Your Attic?

For most of us, the attic is a place to store clothes, luggage and old family photos, but for energy researchers it’s a hot topic of discussion. In the last several decades, building codes have called for increased attic insulation.

Most experts contend that a well-ventilated attic keeps the house more comfortable in summer and guards against moist, heated air building up in winter. There are also dissenting voices who say that the benefits of ventilation are overrated.

Who’s right? Obviously more research is needed, but here’s what we do know:

  • Don’t avoid ventilating your attic for fear you’re letting cold air into the house. Your actual living space is sealed and insulated at the attic floor—the attic is outside this envelope.
  • If there are asphalt shingles on your roof, the attic must be ventilated to comply with the terms of the manufacturer’s warranty.
  • One reason for the lack of agreement over attic ventilation is the tremendous variation in climate across North America. Rarely will you find a building practice that works everywhere.

For instance, attic ventilation is used widely in cold climates to evacuate the warm, moist air that escapes from the living space below. If this air lingers, it can condense on the underside of the roof sheathing and rot it. A healthy airflow also helps with ice dams, which begin to form when warm air in the attic melts the snow from beneath and creates runoff that refreezes on the colder eave. Great, but neither of these problems is experienced in warmer climates.