Double doors often require a hardware device known as an "astragal." The astragal helps seal the gap between pairs of doors, and is used to block sound or air drafts. Before you install an astragal, you must first determine how your doors are configured, as well as what size astragal you need to use. By taking the time to choose the correct installation techniques, you greatly improve your chances of a successful installation.
Determine which leaf of the door is the active leaf. On a pair of doors, one door is typically considered active, while the other is inactive or stationary. If a lock is already installed, the door with the lock is considered the active leaf. If no lock is present, choose the door that is most convenient for users as the active leaf. For example, a door that provides easy access to the room's light switch would generally be considered the active of the two leafs.
Hand the doors. The handing of a door describes which way it swings within an opening. Pairs of doors can have either a reverse or regular handing. Stand on the secure side of the door (the side where you need a key to enter). If the doors open toward you, they are reverse handed (also known as reverse swing or reverse bevel). If they open away from you, the doors are regular-handed-
Decide where the astragal should be installed. In order for the astragal to function properly, it should be installed on the pull side (the side where the doors pull toward you) of the active leaf on reverse bevel doors. On regular swing doors, the astragl is installed on the push side of the inactive leaf.
Measure the height of your doors, as well as the space between the two leafs. Choose an astragal that is the same height as your doors, and will fit into the space between the doors.
Cut the astragal to the height of the doors using a hacksaw, if needed.
Wrap the astragal around the edge of the door, starting at the top. Make sure the top of the astragal is aligned with the top of the door, then press the astragal firmly in place down the length of the door.
Pre-drill holes in the door for the screws. Drill these holes with a bit that is one size smaller than the screws provided with your astragal. Pre-drill all applicable holes in the astragal along the edge of the door.
Screw the astragal into place using the fasteners provided. If your astragl came with plastic edge covers, slide them over the edge of the door to cover the screws.