How to Build a Homemade Rafter Vent

Measure the spaces in the attic between your rafters and the distance along the roof deck that your rafter vent will cover. Make your rafter vents long enough -- so that the lower end is directly above the soffit vent and the upper end has at least 6 inches of clearance above your insulation.

Mark the dimensions you measured in the attic on a piece of sheet metal. Cut the sheet metal according to your measurements, using the tin snips. Mark holes at each corner of one end of your metal sheet and at the mid point of its length. Place the holes at the corners 2 inches away from the short side of the sheet, with a half-inch gap between the holes at the middle and the long sides of the sheet. Drill out each hole using a one-fourth-inch metal drill bit. After the holes are drilled, remove any burs left around the holes.

Using your measuring tape, mark a straight line down the length of the sheet metal, 1 inch away from the holes at the corners for the long sides of the sheet. Create two parallel lines 2 inches toward the center of the sheet from the lines you just marked.

Place the marked piece of metal on a hard surface with a straight edge, such as a workbench or table. Position the metal sheet so that the first mark is directly above the edge of the table. Clamp the metal to the table so that it cannot move, and place the wood block on top of the sheet metal sticking out from the table. Slowly apply downward pressure on the block, so that the metal is bent until it points straight down.

Unclamp the sheet metal and flip it over, so that the side you just bent faces up and the second line marked on that side is above the edge of the table. Reclamp the sheet metal, and use the wood block to bend the metal sticking over the table straight down, without altering the first bend. Repeat this process for the other side of the sheet.