Greenheck has developed a UL-approved three-sided retaining angle installation method for fire and combination fire smoke dampers. The company says this method is ideal for installations where the damper sleeve is tight up against a wall, floor, or other obstruction with no room for a retaining angle on one side. Greenheck’s installation does not require the use of any firestop material. According to company officials, most three-sided angle installation methods require fire stop material to be applied to a specified minimum thickness on the side of the damper without the retaining angle. Complying with the minimum thickness requirement without scraping off the fire stop material during installation can be difficult, and makes it complicated for building inspectors to confirm that the required amount of fire stop material has been applied.