The screw-down VentSaver model is perfect for mounting on a mechanically fastened metal roof with exposed screw heads. The VentSaver can be anchored directly into either a rafter or wood decking that is at least one inch thick. Additional wood blocking may require access to the underside of the roof and may be necessary when these conditions do not exist. For applications with wood decking that are less than one inch or situations where the pipe is off-center to the panel flat, we recommend the SD (Screw Down) VentSaver Mounting Plate. This plate works with any VentSaver model and comes with 12 three-inch fasteners that can be screwed into at least 1/2" of decking. The plate is 27 inches wide and spans over the high ribs to provide adequate surface area to compensate for off-center pipe placements.