How to Enlarge a Soffit Vent

Remove the small soffit vent's louver, using the correct screwdriver to turn the screws holding the louver in place counterclockwise. The screws hold the louver's flange against the bottom of the soffit. The louver's vanes provide the opening for the air to circulate into the attic.

Peel the insect screen from the soffit vent opening, using pliers for leverage. Soffit installers place an insect screen over the vent opening and secure the screen to the soffit with an exterior caulk. Insect screens look like a metal-fibered window screen.

Measure the length and width of the new louver's vanes with a tape measure. Louver manufacturers usually state the vane size, sometimes called the "Opening size," on the louver's packaging. Transfer the vane's measurements to the soffit, using a pencil to place measurement marks at the appropriate places.

Draw straight lines between the measurement marks with the pencil, using a straightedge as a guide. The pencil lines act as a cutting guide.

Measure the thickness of wood covering the soffit with the tape measure. Adjust a circular saw's blade guide to this measurement, using the circular saw manufacturer's instructions.

Put on safety glasses.

Hold the circular saw's blade on one end of one of the pencil lines drawn on the soffit. Cut the soffit along the pencil line, stopping the saw as its blade reaches the far end of the pencil line. Cut all four sides of the outline using the same method.

Hold a wood chisel's blade on one of the outline's corners and strike the chisel's handle with a hammer until the blade cuts through the soffit. Repeat this procedure at each corner. The circular saw's round blade leaves a small amount of wood uncut at each corner. The wood chisel completes the cut.

Remove the nails holding the enlarged vent cutout from the soffit, using a pry bar for leverage. Usually 1-inch nails hold the soffit material to the eave's trusses. After pulling out all of the nails, discard the vent cutout.

Secure the soffit material around the enlarged vent cutout to the eave trusses with 1-inch ring-shank nails, using a hammer to drive a nail into each truss. Keep the nails about 1/2 inch away from the vent opening. The nails hold the loose edge of the cutout tight to the eave's trusses, eliminating the possibility of future wind damage.

Run a 1/8-inch-wide bead of exterior-grade caulk around the perimeter of the soffit's vent opening, using a caulking gun to apply the caulking.

Center an insect screen over the soffit's vent opening. Press the insect screen into the caulking.

Press a soffit vent louver against the vent opening. Secure the louver to the soffit with the louver-manufacturer supplied screws, using the correct screwdriver to turn each screw clockwise until the screw's head is snug against the louver's surface. Place a screw in each of the louver's screw holes, located in the louver's flange.