How to Build a Wooden Window Box

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This article will teach you how to make a wooden window box.  A wooden window box will generally last 3-7 years before it begins to show signs of rot and deterioration.  There are many online companies now that sell no rot window boxes made from composites, PVC, fiberglass, or moulded plastics.  With so many great material choices fewer and fewer people are still making window boxes out of wood since the material choice is less than ideal for an application with so much direct contact with water and insects.  Below, however, is step-by-step instructions for how to build your own window box out of wood in case you are wanting to save money or just like the look of a wooden box.  

I recommend using cedar as the choice of wood and you can get the materials for your window boxes from home depot or lowes home improvement store.

Material List

12' x 3/4" x 7.25" Cedar board

Exterior wood glue

Quart primer and exterior latex paint or stain

Caulk

Wood filler

#6 x 2" Trim head screws, qty=30-50

60 grit orbital sand paper, 220 grit orbital sand paper

Tools Needed

Drill

1/8" wood drill bit with counter sink

Tape measure and pencil

Chop saw

Hand sander

Caulk gun

Paint brush, roller, and pan

Step 1: Cut your 3/4" thick x 7.25"Wide cedar board into 5 pieces.  We are going to build a 36" long window box.  

36" Long x 1 (Front Board)

34.75" Long x 2 (Bottom and Back Boards)

8" Long x 2 (Side Pieces)

Step 2: Attach the side pieces to the front board with a butt joint.  First dry connect them by drilling a pilot 1/8" countersinking hole through the front board and into the sides pieces.  You will need to pre-drill 3 holes to connect them; one at the top, middle, and bottom.  Next, apply exterior rated wood glue and secure the two pieces with three #6 x 2" trim head screws to connect the pieces.  Repeat with the other side pieces until connected.

Step 3: Next dry attach the bottom board using the same 1/8" pilot countersinking hole drill bit.  You want to make sure you countersink the hole at least 1/4" deep so that when you screw the trim head screws in it does not split the wood.  You'll be sinking the head of the screw into the surface leaving a visible hole that you will fill with wood filler later on.  I recommend to put a screw every 6-8" so that the box is tight and strong.  You can reference the overhead view picture above.  After you dry fit, then apply wood glue and repeat this time screwing the screws to connect the bottom board to the front and sides.

Step 4: Repeat the process with the back board doing a dry fit first with countersinking 1/8" pilot hole followed by glue and screws.  

Step 5: Once the box is glued together use your wood filler to fill each of the countersunk holes.  Next, set the box aside to dry for several hours.  Wipe any visible glue first though as sanding it off later will be time consuming.

Step 6: Next use a palm sander and 60 grit sand paper to flatten out the seams of the window box and to remove any excess wood filler.  After grinding with heavy grit sand paper you can switch to a 220 grit to polish the box up and get it ready for painting.

Step 7: Apply caulk to the inside seams of the box and let dry for a couple hours.

Step 8: Prime the entire window box both inside and outside.  Priming the inside will help seal the wood and protect it longer from water and insects.  Let dry for two hours then come back and apply two coats of exterior latex paint to the outer surface using a brush and/or roller.

And that's it! Using wood from home depot or lowes to make wooden window boxes is a moderate process.  Remember that wooden window boxes will require maintenance.  I suggest to take the flower boxes down during the winter and empty out the soil to avoid splitting and cracking.  Each winter you should inspect the window planter and touch up with paint as you see fit.  With proper maintenance each winter you can make a wooden window box last 10 years.

About the Author:

Matthew Buquoi is the owner of Flower Window Boxes, a no rot PVC window box company specializing in custom, self-watering window boxes that ship all over the country.