How to Make an Exterior Door Jamb

Having an exterior door jamb on each entrance to your home adds a more finished look to the doorways. As well, weatherstripping mounted on the door jamb helps prevent heat from escaping out of the house. Follow these steps to make an exterior door jamb, using precut weather-stripped planks.

Step 1: Measure and Trim the Doorjamb Planks to Size

Measure the right and left vertical sides of the door frame, from the base of the frame to the top. Mark each measurement on a separate 8-foot doorjamb plank, and cut them to the correct size with the circular saw.

Step 2: Measure the Top of the Door Jamb

Temporarily insert the vertical doorjamb planks into the door frame, and have a helper hold them in place. Measure across the top of the door frame to the inside edges of the two doorjamb planks. Mark this length on the six-foot doorjamb plank, and cut it to size.

Step 3: Fasten the 3 Sides of the Exterior Door Jamb

Align the three sides of the door jamb into an upside-down U, so the weatherstripped edge faces toward the inside of your house. Before nailing them together, check with the carpenter's level and square that they form 90-degree angles. Use the finishing nailer, attached to its air compressor, to nail the vertical planks to the top horizontal plank. Drive the nails through the side planks into the top plank.

Step 4: Insert the Door Jamb into the Door Frame

Insert the vertical sides and top of the exterior door jamb into the door frame. Use the carpenter's square and level to ensure 90-degree angles as you insert small wood shims into the sides and top of the door frame.

These hold the door jamb in place, keeping the sides vertical and top perpendicular. Check and adjust the shims as needed. You will need at least two shims for each corner and for the center of the top plank, along with six for each vertical side.

Step 5: Fasten the Door Jamb to the Frame and Finish With Trim

Attach the framing nailer to the air compressor. Nail the exterior door jamb to the door frame at the shim spots. Trim off excess shims with a box cutter knife.

Step 6: Add Threshold and Trim

Measure and lay out the threshold so it covers the interior floor space about six inches inside the door. It should align exactly with the concrete threshold step at the exterior of the door.

Measure and cut the plain trim for around the door on both sides, interior and exterior. Miter the corners at 45 degrees. Check with the level and square to make sure the trim planks are at 90 degrees vertical and horizontal. Nail the trim to the wall with the finishing nailer.