Installing Soffit Vents

A good attic ventilation system can save you a bundle on air-conditioning costs. Soffit vents (also called under-eave vents) are ideal for drawing cool fresh air into the attic as the hot, stale air is exhausted through ridge, gable or turbine vents. Most new houses are built with soffit vents, but older homes rarely have them. If that's the case at your place, add soffit vents, and give your attic a breather. (You may want to check out our articles on installing gable vents and ridge vents.)

If you have wood-clad soffits, you can follow these step-by-step instructions and do the job yourself in a day or two. If you'd rather hire a pro as you probably should if you have stucco to contend with check out our Services channel. We'll help you find a trustworthy, prescreened professional.

Soffit vent: simple view
Step by Step
1. Check the attic. For soffit vents to work properly, the interior eave area must be clear of insulation or any other material. Go into the attic with a flashlight and inspect the area just above where you'll install the vents. This is the area between the fascia board and the house wall, which is marked in the attic by the top plate(s). (If you need to move insulation out of the way, make sure to wear a dust mask, a long-sleeved shirt and goggles.) As you clear the area, take note of how the framing members are spaced. You'll want to install your vents where air won't be blocked by soffit joists, rafters and the like.

2. Pick your vents. Soffit vents are available in two general styles. There are long narrow strips designed to butt together in one continuous vent, and wider individual vents designed to fit between soffit joists, as shown in the drawing. Use the narrow, continuous vent if your soffits are less than 16 inches wide, but if they're wider use individual vents. These are much easier to install. Either way, intake vent capacity should match or exceed the capacity of your exhaust vents. Vent capacity is measured as net free ventilation area (NFVA, or "free area"). NFVA should be listed on any type of vent you buy.

Soffit vent: detailed view
Plastic, aluminum and steel vents work equally well, but typically they come only in white and brown. Buy mill finish (unpainted) aluminum vents if you want to paint them to match your house. Use corrosion-resistant screws to mount each vent. (Bronze, galvanized and stainless steel screws are among those that resist corrosion.) If the vents don't come with their own installation screws, use #4 by 1/2-inch, stainless steel pan-head screws.

3. Lay out the openings. Lay out the vent openings in the middle of the soffit overhang, so you'll have ample room to maneuver your saw. Size each opening so that the outer lip, or flange, of the vent will overlap the edge of the hole. Snap two parallel chalk lines to define the opening width along the entire length of the soffit. Then use a try square or carpenter's square to mark the ends of each opening. Drill a 3/4-inch diameter hole inside your layout lines, and stick a tape measure or ruler through the hole to measure the thickness of your soffit material. Pick positions for individual vents between the rafters. (You'll know the rafter spacing from your trip into the attic, and you can find the first one by poking a piece of stiff wire or a bent wire coat hanger through the hole you just made and exploring with it.)

4. Cut the openings. Use a power saw to cut along the lines you've marked. Once you've made all your lengthwise cuts, cut the ends of each vent hole with a portable jigsaw or a keyhole saw.

Note: If you're installing individual vents, a reciprocating saw or jigsaw will be easier to handle (if a bit slower) than a circular saw. No matter what kind of saw you use, always wear protective goggles and a dust mask. To make "pocket" cuts with your circular saw cuts that start in the middle of a board instead of at its edge see our article on circular saw tips.

To make the long, straight cuts you'll need for a continuous vent, use a circular saw with carbide-tipped ripping (or framing) blade. Make this process easier by screwing a 1-by-2 or 1-by-4 guide strip in place under the soffit to guide the saw, and adjust the blade depth so that it's about 1/8 inch greater than the thickness of your soffit material. This ensures that you'll cut all the way through the soffit and just graze but not damage the soffit joists. If you don't have a cordless circular saw to make these cuts, now is a great time to buy or borrow one. You'll appreciate the lighter weight and easy maneuverability when you're working overhead.

5. Install the vents. If your vents don't come with screw holes, drill one in each corner of the installation flange and then every 12 to 14 inches. A cordless drill is the best tool for this, and for driving the installation screws. You'll need a helper to hold a continuous soffit vent in place while you install it. Individual vents are small enough to install yourself.

Tim Snyder, writer, photographer and carpenter, was a senior editor at Fine Homebuilding magazine and executive editor of American Woodworker magazine. With TV personality Norm Abram, Snyder coauthored two books in the best-selling New Yankee Workshop series. He's also written books on deck design and furniture making. recommended tools & supplies:

  • Chalk line

  • Individual soffit vents

  • Tape measure

  • Continuous soffit vents

  • Carpenter's square

  • Try square

  • Phillips head screws

  • Circular saw

  • Cordless circular saw

  • Carbide-tipped ripping/framing blade

  • Reciprocating saw

  • Jigsaw

  • Keyhole saw

  • Cordless drill

  • Dust mask

  • Protective goggles