To install vents on a metal roof, lay the outline for cuts in the roof, cut holes for the vents, apply tar to the edges of the holes, install the vents and apply more tar to seal them. Avoid installing vents on weak metal roofs with no sub-roof.
Begin by selecting the type of vents to install, which may include whirlybird vents or slatted vents. Decide where the vents are to be placed based on the type of vent and the size of the roof, and mark the area with chalk. Use a tape measure to determine the size of the vents, writing the dimensions on a notepad to use when tracing the outline on the roof. Use a skill saw to cut the hole for each vent, and cover the edges with a thin layer of tar using a small brush.
Drill starter holes where needed, and place the vent over the opening. Screw it into place before applying more tar around the edges to create a stronger seal against air and water. Go to the attic area to apply yet another layer of tar to the underside of the vent. If the vent kit includes a medallion or cover plate, screw it into place at this time.