A door transom is a crosspiece over a door that separates the door from an above window or another door. This is commonly found in French door setups, or older horizontal double doors. Newer home construction will often include a window above the door, and a transom is needed here as well. Before repairing your door transom as well as the wooden door, you want to have all the knowledge at hand before jumping into the process. It can be a complicating process depending on the tools you have at hand. In the end, you will save money by doing the work yourself.
Out With The Old
You will want to remove the old frame including the door. Screw it off the hinges, and place it aside until you know where the old door is going. Then you will want to make two cuts with a circular saw across the width of the threshold. This should be done around 4 inches from each side of the frame of the door, or as close as your saw will allow you to go. Try not to cut into it too deeply. Remove the frame, leaving a small piece on each side. If it does not come out easily, you will want to remove any nails that may be holding onto it by using a wood chisel to carefully remove the frame. Make sure the frame is completely removed.
In With The New
Make sure your new door and frame fit into the doorway. You cannot just stick the frame into place and nail it shut. You have to raise, and hold the frame securely, and then insert the shims on top, and down under to give it the most support. Attach the shims along the length of the frame under the inside edge of the threshold. Make sure you purchase the right thickness of the shim depending on the thickness of your frame. To get a really tight fit in the threshold, you will want to place a piece of wood between the frame and your hammer and tap it into place.
Once the frame is tightly in place, you will then want to place the construction adhesive over the shims, and tap it back into place. Install the last of the shims into the edges of the threshold firmly. Drill the screws into place throughout the frame tightly. Then place the door hardware into the side of the frame by screwing the plates in. Attach the door to the plates by screwing the pins in. Make sure the door opens and closes comfortably, and the frame is secured onto the threshold. Then you have finished installing your door, and door transom frame.