Window Trim: DIY Window Sill Trim Molding – Easy How To
January 2025
How to Add a Window Sill (When Your House Didn’t Come With One)
If you’re like me and have a builder-basic house, you might have noticed that your windows came with nothing—no sill, no trim, just bare drywall. That’s exactly what I was dealing with! But don’t worry, it’s an easy fix, and I’m going to walk you through how to add a window sill to give your windows that polished, finished look.
From this…
To this…
Shop the room here: You can find the materials I used on my Lowe’s storefront. I’ve also provided separate links for your convenience below. (Please note that these are affiliate links, and I earn a small commission when you make a purchase through them. Your support is greatly appreciated!)
Materials You’ll Need:
- 1×6 Pine Board
- 1×4 Pine Board
- Sherwin-Williams Ultra White
- Wood filler: For filling holes and imperfections.
- Paintable caulk: To seal gaps and create a clean finish. (The painters tape needs to be 1.5″ thick to match the thickness of the wood).
- Brad nails: Various sizes for different parts of the build.
- Painters Tape
- Paint roller
Tools You’ll Need:
- jig-saw
- Nail gun: Makes assembly faster.
- Miter Saw
- Tape Measure: This one lock.
- Nail Punch
- Caulk Gun
- Safety Glasses
Step 1: Measure the Window
Start by measuring the width and depth of the window’s inside frame. Be sure to double-check each side for any inconsistencies in case they’re uneven.
Step 2: Cut the Stool Length
Cut a 1×6 board using a miter saw to the window’s width, adding 2 inches (1 inch on each side) for an overhang.
Step 3: Measure the Depth
Measure the depth of the window from the top to the bottom, checking both sides. If they’re not perfectly even, be sure to account for this in your measurements.
Step 4: Mark the Cuts
Mark the 1×6 board where you’ll be making the cuts, using a pencil along the outer edge of the board. This will guide your cuts.
Step 5: Cut the Board
Secure the board with clamps and use a jigsaw to carefully cut along your marked line. Take your time to ensure a clean, straight cut.
Step 6: Fit and Nail Down the Stool
Place the cut board inside the window frame. Check that it’s level, adjusting as needed. In my case, I had textured orange peel walls in Florida, so I had to do some sanding to get everything even. Once the board is level and fits well, use a brad nailer to secure it in place. Next, measure from edge to edge underneath the sill to check for any differences in window sizes. Make sure everything is squared up.
Step 8: Cut and Level the Apron
Cut the 1×4 boards that will be used for the apron to the correct size. You will be measuring from the corner of the window to the other corner. Next, place the board under the stool and check for level again. Once everything’s in place, use your brad nailer to attach the 1×4 to the wall under the window stool.
Step 9: Fill Any Gaps
If there are any gaps from imperfect cuts (like I had with the jigsaw), fill them with wood filler. Smooth out the filler and wipe away any excess with a damp rag.
Step 10: Caulk, Tape and Paint
Caulk any seams for a clean, seamless look. Finally, paint everything. I chose Ultra White to match my baseboards, but you can go with whatever color works best for your space.
You Did It!
Congratulations on giving your bare window some charm, you should be proud of yourself! Ready to dive into your next project? Let’s go!
You got this!
– Audra
