Depending on the area in which you live, there are literally dozens of different insects, birds, and small animals relentlessly seeking refuge in your attic or roof cavity by way of cracks in the decking, soffits or through the most obvious holes on the rooftop: the roof vents. Although they are covered and flashed for rain deflection and drainage issues, there still lies a direct hole and pipe of varying diameter just beneath the cover, and from there, the entry options for a determined intruder get nothing but better. Blocking pests at the rooftop -- before they can enter a vent -- is imperative, and can be accomplished with just a few basic tools and materials.
Pattern Cutout and Assembly
Measure the top plane of the entire vent assembly. Mark this rectangle on the center of a large piece of vent screen, using a marker. Measure downward to the rooftop at all four corners to determine the height. Transfer the lines for the height in all four directions from all four corners of the original rectangle -- this will make eight lines, plus an edge line for each of these tabs. Add an additional 1 1/2 inches to each of the lines to fold into a flange for attaching the assembly to the roof.
Cut the triangle-shaped excess screen off of the four corners, using the tin snips. Trim the flange edges to length. Alternatively, for a vertical vent -- such as an attic vent -- measure the entire rectangle behind the frame molding, and then cut it to size, using tin snips. Place the molding over the new screen.
Fold the screen 90 degrees, using a board or a step as a straightedge guide. Fold along each edge of the original rectangle, and then fold the last 1 1/2 inches out flat to the same orientation as the rectangle so it seats flat onto the roof. Cut off small pieces of bailing wire and use them as twist ties along the edges that now meet to box the assembly in solidly. Use as many as is necessary to create a tight seam that will be impossible for pests to enter.
Attaching the Assembly
Fit the screen assembly evenly over the vent, keeping the same small gap on all sides. Hammer one wire staple into each corner of the flange to secure the assembly to the roof decking.
Hammer staples evenly into the flange, alternating sides to keep from distorting the box shape as it is pulled in tightly.
Cover each staple generously with asphalt roofing cement to keep water from leaching into the decking material. Alternatively, if the vent was a vertical attic vent, caulk around the entire outside perimeter of the molding frame with exterior-grade caulking.