To determine the rough opening height you must add 5/8” to the overall net height of the frame, if your net frame height is 81”, the rough opening height will be 81 5/8”.
The rough opening width is to be 1¼” over the nominal width, so if your door is 3’0”, then rough opening width will be 37¼”.
It is important to recognize astragal widths on double doors. There are normally two types of astragal, a z-astragal, and a 5/8” astragal (sometimes referred to as a t-astragal). In such instances you can refer to the specification sheet, and consult the factory to determine your rough opening widths.
It is also important to note our frame can not be installed on masonry walls, you must use a sub-buck.