February 23, 2018
Master bedroom window trim

Out with the old. In with the new.

I mentioned in my post about replacing the builder grade trim that I’d be back to outline how we did that for the windows, doors and baseboards. Of this entire project, this was my favorite part. The impact was immediate and the room came to life.

Prep your materials

If you haven’t already, you’ll want to make sure you have all of your supplies. In our research, we found that some people choose to install the trim, prime and paint. It seemed easier to do all of this prior to installation. So, that’s what we did.

To remove the trim, you’ll need:

  • Utility knife
  • Wide tape knife
  • Small pry bar
  • Needle nose pliers
  • Hammer

Remove the old trim

Considering our house was a new build, the trim was easy to remove. You can find a visual tutorial of the best way to do this on The Family Handyman.

As a quick word of advice, don’t take shortcuts removing the trim. Depending on the width of your trim, you don’t want holes in the wall which can be a hassle to fix and slow up your entire process.

Master bedroom window without trim.

Trim removed from around the window. Notice that there is no damage to the walls and all nails have been removed.

Prepping to install the new trim

Once your trim has been primed and painted, it’s ready for install.  You’ll need quite a few things to make this happen.

  • Pneumatic trim nailer
  • Brad nails
  • Air compressor
  • Measuring tape
  • Combination square
  • Level
  • Safety glasses
  • Clamps
  • Wood glue

Measure a million times and cut once

We removed all of the existing trim, then took measurements for the new trim. It’s important to know what parts of the windows and doors are what to make sure you’re cutting the right boards. Based on the trim we decided to install, the image below outlines the pieces in play.

Section of window trim clarification

Now that you know what is what, you want to make cuts in a particular order to make sure everything fits.

  1. Head casing. To get this size, measure the window and add your casing width plus any overhang you want. Example: Let’s say the window is 48 inches, the casing is 4 inches and you want a 1 inch overhang on both sides. You need your head casing to be 48 + 8 (2 x 4 inch casings) + 2 (2 x 1 inch overhangs) = 58 inches.
  2.  Cap. Take the length of the head casing and add the amount of overhang you’d like. We did an inch. Example: 58 inch head casing and 1 inch overhang on the cap for each side means a 60 inch cap.
  3. Stool:  We cut this the same length as the head casing for a balanced look.
  4. Apron: This should be the width of the window + the width of the casing.
  5. Casing: Measure the length on these pieces once the top and bottom of the trim is installed. This way, you’ll get the exact measurement you need.
Measure correctly to achieve a layered look.

Measuring is critical to get the look you want. If you are going for a heavily layered look, it’s important to stagger your material length.

Pre-assemble where you can

Now that you have your head casing, cap, stool and apron measured, you’ll want to assemble those pieces prior to install. It reduces the total amount of pieces and likelihood for errors. To attach the cap to the head casing:

  • Measure the planned overhang on the cap and make a light mark in pencil.
  • Lightly apply wood glue to the head casing.
  • Place the head casing on the cap and firmly hold in place.
  • Clamp the head casing and cap together.
  • Nail the two pieces with your brad nails.
  • Let dry.
  • Repeat this process for the stool and apron.

Once the boards are dry, you can begin the installation.

Installing the trim

The most important part of installing window trim is measuring. You need to measure for center, your reveal and level. Do not rush this part of the process. The beauty of trim is in the details. You will notice if something is off.

Start installation with the cap and head casing.

  • Determine your reveal and mark it out around the window/door with a combination square.
  • Find center of the window.
  • Find the center of your assembled piece.
  • Match up the center of the window to the center of your cap and head casing.
  • Match up the boards to the intended reveal.
  • Place a long level on top of the boards and find level.

Now is a good time to step back and make sure the trim looks good. If everything looks as planned, carry on! If not, determine what’s not right and fix it.

  • Have one person hold the trim.
  • Insert the first nail on the edge of the board.
  • Check for level.
  • If everything looks good, place a nail 16-18 inches from the first.
  • Check for level.
  • Repeat until the trim is installed for each section.

Next, do the exact same thing for the stool and apron. As you work on this, keep in mind that you don’t need a ton of nails to securely attach the boards. Plus, you don’t want a boatload of nail holes to fill and paint.

Measuring the casing

Now that the top and bottom of the trim are installed, measure the casing length. Measure and cut each side. Don’t do bulk cuts. While they should be the same, it’s not worth wasting a board. Be sure to cut a little long as you are going for a perfect fit. Caulk can work wonders, but you want the cuts to be as close to perfect as possible.

Once the casing is ready to go, follow the process outlined above and you’ll have something that looks like this:

Window trim is now installed.

All the trim is now installed. Take note of how few nails are used. (Ignore the messy bed. The dogs were supervising.)

The finishes touches

Now that the trim is installed, fill the nail holes. Don’t rush this. I love DAP DryDex for nail hole filling. It’s easy to apply from the tube, sand and takes paint well. I find that two coats and rounds of sanding are the norm for filling in nail holes evenly. Anything less and I end up with an obvious pit.

Once your nail holes are filled and sanded, lightly apply a layer of paint with a foam roller. Depending on the paint used, you’ll likely need two coats. Once the paint is applied, you’ll want to add a caulk to the seams. I love DAP Dynaflex 230 in white. It’s super easy to work with and matched my white color perfectly.

Make your trim seamless with caulk.

Despite my best efforts the trim wasn’t completely flush with the wall. Fortunately, this nothing a little caulk can’t fix!


Get a seamless look with DAP Dynaflex 230

Adding caulk gives the trim a finished look. When installed correctly, it’s should be seamless.

A whole new look

Before: I don’t have a good photo of the master, but the window looked the exact same.

Image of builder grade time

Builder grade trim

After: A little trim can go a long way. The trim with the shiplap wall really brings this room to life.

The final product improves the room.

A little trim can go a long way!


In full transparency, this was a simple installation of trim. I’ve read a few other blogs about swapping out trim and the need to rebuild the window jamb, sill and whatever else. Fortunately, we didn’t have to do any of that.

You Might Also Like