How to Install Exterior Door Casing

burgundy front door with brass hardware
What You'll Need
Exterior door casing
8d finish nails
Nail set
Door shims
Measuring tape
Wood putty
Putty knife

When an exterior door is being installed, it consists of two very important parts: an exterior door casing and the door. Installing the exterior door casing correctly is very important. The information that follows will explain how you can easily install an exterior wood casing yourself.

Step 1 - Take Measurements

One of the great things about an exterior door casing is that you can purchase them already built. This saves a lot of time and a ton of guessing but you'll still need to have the correct exterior door casing or the job will not work well or be easy. It is incredibly important that you use the measuring tape to get the correct width, height, and depth of the doorway. This will enable you to purchase the correct exterior door casing. The sizing will rarely be perfect, which is why shims are used.

Step 2 - Drill Pilot Holes

drill and bits laying on a wood surface

To save yourself time and a headache later on you should always drill pilot holes before you place the door casing in the frame. Before drilling the holes always place the new casing in place to test the fitting. If you are satisfied it will work you can remove it and lay it on a flat surface. Use the hacksaw and remove the head off of one of the nails. Place this trimmed nail into the drill as a drill bit. Use the measuring tape and make four evenly spaced marks with your pencil along both vertical sides of the casing. It will be easier to make the pilot holes from the outside of the casing.

Step 3 - Set the Exterior Door Casing

These holes make it much easier for you to attach the door casing to the frame. Set the exterior door casing in place. Adjust the casing as much as you need in order to make sure that it is spaced correctly and centered. Once the door casing is in place you can begin bracing it with wood shims. Place enough shims along the sides of the casing in order to secure it in place and then tack it in place with a single nail.

Step 4 - Secure the Casing

pile of door shims

The door casing will not move so you can make sure it is properly set in the frame. Use the level and place it on the inside of the casing. The green liquid should be centered. Repeat with the other side of the casing. If the casing is not plumb then adjust the shims as needed. On the plumbed side of the casing secure it in place with shims and nails. Repeat the same procedure with the top of the casing. Once the top is complete continue around the casing adding shims and nails. Once all of the nails are in place make use of the nail set to push each nail far into the casing. Apply wood putty to the nail holes and scrape the excess away with the putty knife.