How to Build a Window Box

We’ve been considering adding window boxes to our house for a while. But before I built a bunch of them, I decided to build one first and place it on one of the windows near our pool area. That way, we could see how it looks and decide if we want to add them to the front of the house. I documented the whole process to show you how to build your own window box!

How to Build a DIY Window Box

Before we get started, here is a list of the tools and materials you’ll need. Of course, you’ll need to make some adjustments based on how many you are building and how long they need to be.

I made the decision to build them out of PVC to avoid issues with wood rot.

Tools and Materials

  • (1) 1x8x10′ smooth PVC board
  • (1) 1x3x8′ smooth PVC board
  • (1) 1x2x8′ smooth PVC board
  • (1) smooth PVC cove moulding
  • PVC cement
  • Caulk
  • Finish nailer
  • 1 1/4″ finish nails
  • 1 1/2″ Tapcon screws (for brick)
  • 1 1/2″ wood screws (for siding)
  • miter saw
  • table saw
  • tape measure

Step 1: Measure the Window

Before I built the window box, the first thing I did was measure the window where I would be placing it. This particular window was 32 inches wide. So this is how wide I decided to make the window box. I’ve seen window boxes that are wider than the window, but it’s most common to make them the same width as the window.

Step 2: Make All of the Cuts

Next, I cut all of the PVC pieces for the window box. Here is a list of the cuts I made. Keep in mind that you’ll need to adjust the lengths for the size you are building.

  • (2) 1×8 @ 32 inches
  • (1) 1×8 ripped to 6 1/2″ @ 32 inches
  • (2) 1×8 @ 8 inches
  • (1) 1×2 @ 33 1/2″ mitered on both ends
  • (2) 1×2 @ 8 1/2″ mitered on one end
  • (1) 1×2 @ 30 1/2″
  • (2) 1×3 @ 30 1/2 mitered length-wise on the table saw (cleat)

Step 3: Build the Box

After I had all of the pieces cut, I started building the box. First, I applied PVC cement to the long edge of the ripped 1×8. And used the finish nailer to fasten it to one of the 32″ long 1x8s, set in 3/4″ from the edge.

Then I applied PVC cement to both ends and fastened the 8″ 1x8s to the ends with the finish nailer as shown.

After I had both ends on, I applied PVC cement to the front edges and fastened the other 32″ long 1×8 on the front.

Step 4: Add the Trim

After I had the box built, I applied PC cement to the top edges. Then I fastened the 1x2s in place with the finish nailer. Then I added some cement to the back of the cove moulding and placed them as shown below the 1x2s.

Step 5: Add the Cleat

Next, I added PVC cement to the back of the cleat and fastened it to the back of the box, as shown.

Step 6: Drill Drain Holes

Using a 1/2″ drill bit, I drilled three holes in the bottom of the box to allow water to drain out.

Step 7: Paint the Window Box

We had a difficult time deciding what color to paint the window box but finally decided that it would be best if it had some contrast with the house color. so we decided to go with Sherwin Williams Iron Ore.

Step 8: Install the Window Box

I used a level to mark a straight line below the window. Then I drill three pilot holes through the cleat. I placed the cleat on the line and made marks on the brick through the holes. Using the hammer drill fitted with a masonry bit, I drilled pilot holes on each of those marks. Then I fastened the other cleat to the wall using Tapcon screws. Finally, I slid the window box onto the wall-mounted cleat.

Step 9: Plant Some Flowers

The final step of any window box installation is to add some flowers and plants. Since this area of our house doesn’t get a lot of direct sunlight, we chose some plants and flowers that thrive in the shade. We also added some potting mix to the bottom and around the plants.

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  • Reply Trudi Alderman McDaniel

    These look lovely! I’m curious if drainage holes are necessary for window boxes? I’ve seen some put them and some not.

    April 25, 2023 at 2:45 pm
  • Reply Sue P.

    We, too, live in Kingsport and my husband just made 6 window boxes for our front porch rails. Our metal troughs had begun to rust out, so rather than replacing them, he used PVC boards just as you did — great minds think alike! Our house is dark blue so we’re just leaving them white. He bought cast iron decorative brackets to attach them to the porch balustrade. They look great! I’m waiting another 10 days or so for the freeze warnings to pass before filling them with plants.

    April 26, 2023 at 1:39 pm
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