Hardwood Door Jambs A solid and strong door jamb is crucial for ensuring that your door stops, opens and closes properly. A broken or damaged jamb can make it difficult to open and close your doors, as well as lead to damage to your hinges. How to Install a Door Jamb The first step in installing a hardwood door jambs is to determine the proper width for your door opening. For this, you’ll need to know the wall stud thickness and the sheetrock thickness. You can use a stud finder to measure the studs. Then, use the rough opening measurements to choose a jamb that will fit inside the wall and be flush with the wall framing. Once you’ve determined the jamb width, cut the two side jambs to length and fasten them to the studs with 8d finish nails. Leave at least 1/8 inch of space between the jambs for door clearance. Hinge Mortise Next, cut shallow recesses, called hinge mortises, into the jamb to support the door hinges. You can do this with a router, or by hand with a sharp wood chisel