How to Install an Exterior Door

Exterior doors can be heavy and cumbersome, especially insulated doors made of steel. Some wood front doors can also be quite heavy. No matter what kind of door you select, ask someone to help you with your door installation. Working with another person will make the job easier.

To put in a new pre-hung door, you will need to prepare the rough opening of the door. If you’re replacing an existing door, it needs to be removed. Below are basic tips for removing a door and frame:

• With the door open, unscrew the hinges. The person helping you can hold the door as you separate it from the hinges and take it out of the frame.
• Use a drop cloth or cardboard to protect floors from scratches.
• Take off the doorknob and other hardware. You may be able to re-use them.
• If the door is painted shut, cut through the paint first with a sharp utility knife to avoid damaging trim.
• Use a pry bar to take out the old frame and remove any stubborn nails or screws.
• If you’re removing the trim, cut it into smaller sections.
• Minimize damage to walls by removing the door frame from top to bottom.

Tip: For demolition projects, always where safety equipment such as gloves and eye protection.

An important step in knowing how to install an exterior door is to take accurate measurements. if the new door has the same measurements as the old door, installing an exterior door is easier. To get accurate measurements for a pre-hung door:

• Measure the height of your home's door opening first. You will measure vertically from the floor to the top of the door jamb.
• Next, determine the width of the doorway. Measure from side to side once near the top of the doorway. Make the next measurement in the middle of the doorway. The third width measurement should be close to the bottom of the doorway. If the three width measurements aren’t the same, use the shortest one.
• Finally, you need to know the width of the door jamb. On one side of the door jamb, measure from the front edge of the door frame to the back edge of the door frame. 

Before unpacking the new door, measure the rough opening of the doorway to double check that the new door is the right size. Once your new door is out of the package, measure it to make sure it will fit before you start installing it. During installation, leave the retaining brackets that hold the door closed in place. 

• Center the door and frame in the rough opening as a test fit.
• Use a level to make sure the door is plumb.
• If necessary, shim under the lower side jamb until the door is plumb.
• Adjust as necessary to keep the door jambs square with each other.
• Double check to make sure the door is centered.

• Trace the outline of the moulding onto the siding.
• If you have vinyl siding or metal siding, be sure to enlarge the outline to make room for the extra trim required.
• Remove the door frame after finishing the outline.

• Cut along the outline down to the sheathing.
• With your safety glasses on, start the cut with the blade clear of the siding, and then lower the moving blade into it.
• Stop just short of the corners to prevent damaging the siding that will remain.
• Finish the corners with a sharp wood chisel.
• Cut a piece of the drip edge to fit the width of the rough opening.
• To provide a moisture barrier, apply building paper to the exposed areas of the walls and door frame.
• Cut the drip edge to fit the width of the rough opening and slide it underneath the siding at the top of the opening.
• Do not nail the drip edge.

• Check the fit before installing a new door, and enlarge the opening as necessary.
• Once you are satisfied with the fit of the door, remove it and apply several thick beads of silicone caulk to the bottom of the doorsill.
• Caulk underneath the spots where the bottom of the jamb and brick moulding will be.

• Center the door in the rough opening.
• Push the moulding tight against the sheathing.

• Check that the door jamb on the hinge side is plumb and shim as necessary.
• Temporarily screw the hinge jamb in place.
• Loosen the screws if necessary to bring the jamb back into plumb.

• Cut pairs of wedge-shaped cedar shims together to form flat shims.
• Using another entrance, go inside and insert them into the gaps behind the hinges and between the jamb and framing to stabilize the jamb.
• Cedar shims are preferable to pine because they are more weather-resistant.

• Install the door hinges provided by the manufacturer.
• Secure them to the frame with the included hardware.

• Remove the retaining brackets installed by the manufacturer.
• Open and close the door to make sure it works properly.

• Remove two of the screws on the top hinge and replace with long anchor screws. These anchor screws will penetrate the framing members to strengthen the installation.
• Do not use longer screws than the manufacturer calls for on doors with sidelights — the screws might break the glass.

• Anchor the moulding to the door frame with 10d galvanized nails every 12 inches.
• Use a nail set to drive the nail heads below the surface of the wood.

• Apply paintable caulk and insulate around the entire door frame.
• Fill all nail holes with caulk and insulate with weather stripping where applicable.
• Finish the door as directed by the manufacturer.If the threshold is adjustable, adjust it for a tight seal as directed by the manufacturer.

Tip: If you set the threshold too high, it will make the door difficult to open and eventually could damage either the door or the weather stripping.

• If the trim was damaged during removal of the old door, cut and install new casing.
• Cut the shims flush with the framing using a utility knife.

Putting in the doorknob and hardware is the last thing to know about how to install a prehung exterior door.

• Install a new door lock and door knob by inserting the latch through the hole for the new parts.
• Insert the lockset tailpieces through the latch bolt, and screw the handles together by tightening the retaining screws.
• Avoid damage to the screws by using a hand screwdriver.
• Complete the installation by attaching the strike plate to the door jamb to fit the latch bolt.