Improving Attic Ventilation

By: Merle Henkenius (Page 2 of 2)

SNAP TWO parallel chalk lines 2 in. apart along the soffit to represent the cutout for the new strip vent.

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

USE A WIDE, sharp chisel to chop through the soffit at the ends of the vent cutout. A sabre saw is another good option.

HOLD THE 3-in.-wide strip vent centered over the 2-in.-wide cutout in the soffit. Handle it gently to avoid crimping it.

SECURE THE aluminum vent to the plywood soffit with 1/2-in.-long screws spaced 12 to 14 in. apart.

USE A SHORT board or garden rake to pull loose insulation away from the eave so it doesn't block airflow.

STAPLE polystyrene ventilation baffles between the roof rafters to create a path for air to flow up from the newly installed soffit vents.

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Step-by-Step Strip-Vent Installation

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.

Start by using a chalk reel to snap two parallel lines down the center of the soffit (photo 1). Space the lines 2 in. apart; that will allow the vent to overlap the cutout by 1/2 in. on each edge.

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 (photo 2).

When you near the end of the soffit, stop short and connect the two cuts with a sharp chisel or sabre saw (photo 3). 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.

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 (photo 4).

Use a cordless drill/driver to secure the vent to the soffit with 1/2-in.-long No. 4 sheet-metal screws (photo 5). Continue installing additional strip vents until you reach the far end. Trim the last vent to length using aviation snips.

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 (photo 6), or use a garden rake or hoe.

Finally, to ensure that the airway to the vent remains open, staple a ventilation baffle to the plywood sheathing in each rafter bay (photo 7). 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.