Introduction: Building Cedar Trimmed Window Boxes for Your Home

About: It's said that to perfect a skill takes about 10,000 hours of work and study. If that's the case I've got around 9,000 hours to go. But, like they say, it's not the destination but the journey.

Window boxes are an inexpensive and easy way to add beauty and style to a homes exterior. Most often they are nothing more than a simple, painted box filled with flowers or greenery. However, it occurred to me that a window box with more detail and style could improve a homes curb appeal even when empty. To test my theory I built a basic window box and covered it with tongue and groove cedar siding and trim. The result was a incredibally sturdy, unique window box that cost no more than a generic one purchased at a local home and garden center.

Step 1: Materials & Tool List

Your material list will depend on the size and number of window boxes you intend to build. I needed to build three matching units so the materials listed here reflect that. I spent a total of $95 for the supplies listed below, averaging out to a cost of around $32 per box.

To guarantee you build a rugged window box that will stand the test of time I recommend building the basic box using treated lumber. Then trim it out with rough sawn ceder as I did or, for a basic window box, just paint it.

Treated lumber list

1 - 2"x 8" 8 feet in length for the back of the window box. You need the strength of this thicker material to bear the weight of the box when mounting it to the house

3 - 1"x 8" 8 feet in length for the bottom, front and sides of the window box.


3 - 1"x 6" 10 foot long,tongue and groove cedar siding

2 - 1"x 6" 10 foot long, rough sawn cedar boards

Other Items

Box of 2" screws to assemble the window boxes

trim nails (1 1/4") to add cedar siding and trim pieces

12 - 4" (or longer) screws for mounting to your home

Acrylic wood stain (I used Behr all in one wood stain and sealer in a solid white color)


Table Saw, Miter Saw, Nail Gun or hammer, Drill, Lots of Clamps

Step 2: Cutting the Material

The basic window boxes will be built using the treated lumber and then trimmed with the tongue and groove cedar siding and boards. The cut dimensions are as follows:

Treated lumber

Cut the 2" X 8" board into 3, 32" long pieces for the back of the window boxes (note: most 8' boards are usually about 97" actual length). Then rip the boards down to 6" in height.

Cut one of the 1" X 8" boards into 3, 32" long pieces for the bottom of the window boxes

Cut another of the 1" X 8" boards into 3, 32" long pieces for the front of the window boxes. Then rip those boards down to 6 7/8" (or the actual thickness of the bottom board plus 6").

From the last board you will need 6 pieces for the sides. These should approximately 8 3/8" long and ripped to the same height as front pieces.

note: If you just want a basic window box without the cedar trim you will need to modify the dimensions of the front and side pieces so you can hide the screws during assembly. In that case the fronts would be 6" high and the sides would be 6" x 6".


Cedar siding and trim

All 3 tongue and groove boards should be cut into pieces approximately 7 1/2" long.

The 2, 1" x 6" cedar boards will be ripped to create the mitered top cap trim and the upper and lower front and side trim pieces. The upper and lower trim can be sized however you like. Mine were approximately 3/4" tall by 5/16" thick.

Step 3: Assembly - First the Bottom

The first step is to screw the bottom of the window box to the back.

- Lay the back flat on you work surface and, as seen in the photos, clamp the bottom of window box to the back.

- Secure the back so it can't move when you drive the screws (photo #2)

- Drill 7 pilot holes and then screw the bottom to the back

Step 4: Assembly - Next Add the Front

Stand the box on its bottom and position the front as seen in the photos.

- Clamp in place as before.

- Drill 7 pilot holes and screw the front to the box bottom

Step 5: Assembly - Add the Sides

This is where it may get a little dicey. Treated lumber isn't the easiest material to work with and, after just a few days in my garage, the boards were starting to cup. For this reason, I had to use spacers in an effort to straighten and square things up as much as possible.

- The photos illustrate how I used spacers to hold the front of the box square to the bottom and parallel to the back.

- I then clamped the sides to the front and back of the window box and screwed the sides in place.

The result is a window box with an interior space that is 6" x 6" in size. After adding the cedar siding and trim, the overall dimension will be 36" long x 9 5/8" deep x 8 3/8" tall.

Step 6: Adding the Cedar Siding

To install the tongue and groove cedar siding place the window box upside down on your work table. Since the siding was cut 1/2" longer than the box it will extend past the bottom of the box. Assemble and test fit the boards prior to nailing to determine how to best size the boards at each end of the window box.

- The two partial boards, one located at each end of the window box, should be approximately the same size

- Each end board should overhang the ends of the window box the exact thickness of the siding (approximately 3/4") so the side pieces will mate cleanly with the front end boards

- Nail the cedar trim to the window box using the 1 1/4" trim nails using a nail gun or with a hammer. A nail in the middle of each board at both the top and bottom of the board is all you need.

note: You may need to shim the side boards to compensate if the window box is slightly out of square.

Step 7: Drill Drain Holes in the Bottom of the Box

Before adding the rest of the trim drill holes in the bottom of the box so water can drain out.

- With the box still upside down, mark 2 lines on the bottom of the box

- Using a spade bit, drill 1/4" to 3/8" drain holes every 4 inches or so along each line in a staggered fashion

Step 8: Adding a Cedar Cap and Upper and Lower Trim

Cap Trim

- rip the 1" x 6" cedar boards down to around 2 1/4" on the table saw. Next cut into lengths of 37"-38". This will be more than enough material to cut to size on your miter saw.

- Cut a 45 degree miter on one end of a trim piece and line it up with the front left corner of the window box (it will be way too long on the right end).

- Next cut a short piece of cap for one side and check the fit by mating it up to the front cap.

- If your first miter looks good, cut the other end of the front cap, leaving it a little longer than what you think you need.

- Next, cut a short piece of cap for the other side of the window box, try putting it in place and check the fit.

- If the front cap is too long continue to trim in very slightly, multiple times until you get a perfect fit.

- When satisfied, nail the front and side cap trim in place.

- Size and cut the rear cap to fit between the two side caps. I reduced the height of the rear cap (by ripping off approximately a sixteenth of an inch) for a visual effect but this certainly isn't necessary if you prefer all four sides of the top cap are the same thickness.

Upper & Lower Trim

- Cut matching trim pieces from your remaining cedar for under the cap and for the bottom of the window box. My trim pieces were 3/4" tall by 5/16" thick. There is no need to miter the corners of this trim unless you want to. The easier solution is to have the front pieces of trim overhang the ends of the window box and mate the side pieces to the front just like you did with the cedar siding.

Step 9: The Results: Before and After

After staining and mounting the window boxes the results speak for themselves. This project is a great way to add style and personality to your home with a minimal amount of time and money. If your partner has a green thumb and enjoys gardening you are sure to score points if you decide to tackle this project. Better yet, who knows how she will decide to show her gratitude!