DIY Window Trim

20 Materials
4 Hours

Hello, friend! I’m so excited to share my DIY Window Trim Tutorial with you today!

This project took awhile, mostly because we have 8 windows, but the process itself is rather easy. It only requires a few basic tools (miter saw and jigsaw and preferably a brad nailer), but that’s it! (Head to my blog for more DIY projects and decorating inspiration!)

In this photo you can see the trim in progress – even unfinished it added a TON to the space! So let’s get started so you can add some character to your bare windows, too! (P.S. This project came out to about $30-$40 per window, depending on the size. Not bad if you consider how expensive hiring something like this out would be)!

Step 1

Measure how deep your windows are. If they are between 3″-4.5″, you will want to use a 1″x6″ board as your sill. If they are 4.5″-6.5″ deep, you’ll want to use a 1″x8″ board as your sill.

Use the measurements in the materials list below to determine how long your boards need to be.

Step 2

Remove any existing trim you might have. Now measure the length of your window and add 10 inches.

You will cut your 1×8″ to this length – your window length + 10″.

Step 3

Mark 5″ IN from each edge, and however many inches your window depth is DOWN. You are creating the windowsill that will slide into your existing window frame.

Step 4

Using your jigsaw, cut on your lines. Measure 3x, cut once, y’all! (If you have double windows like I do, you’ll need to carefully measure where your next inset needs to be cut out (in the middle of the board your just cut). From the edge of your new cut (see above), measure inwards from each side however long each of your windows is. Now measure DOWN the depth of your windows, connect your lines, and cut out. (If you are only framing out a single window, SKIP this step!)) Sand your board well with 120 grit sandpaper.

Step 5

Install your windowsill into your window using 2″ brad nails and your brad nailer – or a hammer and nails if you don’t have the power version! It should fit snuggly into your window. However, if there are gaps, don’t worry! We’ll fix those with caulking later!

Step 6

Using a tape measure, measure UP from your newly installed windowsill to the top of your window on each side. I measure both sides because sometimes they are slightly different. Cut two 1″x4″ boards to the lengths you just measured. Sand with 120 grit sandpaper. Install these boards on the outside edges of your window with 2″ brad nails and your brad nailer (or hammer/nails). Make sure they are level before you install!

If you have a double window with a middle piece, you’ll need to figure out the width of wood you need there. For one of ours, a 1″x8″ fit perfectly. For the other, I had to piece together two 1″x4″ boards plus a 1″x3″ board. You’ll follow the same process as Step 6 to install this middle piece. Again, if you are only framing a single window, SKIP this paragraph!

Step 7

Now cut your two 1″x2″ boards and your 1″x6″ board to the length of your window plus 7″. Sand them as needed. Assemble your header on the floor, using A LOT of 2″ brad nails and brad nailer (this part is WAY easier using the power nailer – if using hammer and nails you’ll probably need 2 people). You will position the first 1″x2″ on its side, and then on top of your 1″x6″ board so one side is completely flush. In other words, the 1″x2″ board should be protruding out from the 1″x6″ board. CAREFULLY nail together. Repeat on the other side of the 1″x6″ board with your second 1″x2″.

Step 8

Now attach your header to the top of your window above the newly installed 1″x4″ boards. Use 2″ brad nails and use A LOT of them to make sure it’s secure. I suggest driving in one nail every 2-3 inches along the 1″X6″ board. Make sure your header is LEVEL and CENTERED before installing! Cut your last 1″x4″ board to the length of your windows + 7″. Sand as needed. Using 2″ nails, install this board directly underneath your windowsill – with the 1″ side abutting the sill. Again, make sure the board is LEVEL and CENTERED before installing.

Step 9

Using wood fill, fill all of your nail holes (or seams if you have them from any double windows). Allow to dry and then sand smooth.

Step 10

Using paintable caulk, caulk ALL of places where your wood meets your walls or where the wood joins each other at a 90″ angle/corner. Allow to dry.

Step 11

Using a small brush and paint that matches your current wall color, paint around all of the edges of your window where it meets the wall. I did this because the caulk tends to bleed a bit, so this will save you more touch ups at the end. Allow to dry. Using Painters Tape, tape off the exact same places you just painted – where the trim meets the outside walls. You can also tape off your actual windows if you choose.

Using your angled paint brush, paint one coat of primer on your trim. and the inside of your window boxes (this will make the trim and windows look more seamless). Allow to dry. Using your angled brush for the corners/creases and a 4″ foam roller for the flat portions, paint your choice of paint onto your trim/inside of the window boxes. Repeat (2 coats will look much better, trust me).

Step 12

Carefully remove your painters tape about 2 hours after your final coat has been rolled. Use a utility knife to score the tape if necessary. Once the tape has been removed, use a small paint brush and your wall color paint to do any last touch ups.

And that’s it! You’re done! There are a lot of steps, but it’s not a hard project! Just be patient and I promise it will be worth it in the end, because your windows will be FAB! And who doesn’t want FABULOUS windows?!

Happy framing! I hope you'll head to my blog for more inspiration, or check me out on Instagram!

Resources for this project:
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Ana Ochoa - Sunrise Valley Farm Co.
Want more details about this and other DIY projects? Check out my blog post!
Frequently asked questions
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  2 questions
  • Bonnie Bonnie on Sep 11, 2020

    Where did you find that horse art piece or did you make it?

  • Karen Karen on Sep 11, 2020

    I like this trim idea but I want to also incase the inside window sides and top, not leave it to just a coat of paint. I assume (eck!) that would be done after installing the new window sill and before attaching the wall vertical and horizontal trim pieces?

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2 of 13 comments
  • Zitismum Zitismum on Sep 11, 2020

    Nice idea. So many homes have windows with no trim. Think this will be nice in my kitchen where I could use more space on the completely unadorned sill. Love your style., You've created a lovely home!

  • Anna Ibarra Anna Ibarra on Feb 02, 2021

    Love this! Discovered your plate wreath, then your shim board, etc... I’ll drop by your other sites. Great DIY’s. Different DIY’s