Window boxes: Fabrication and Mounting


Window boxes give your home a unique personality and are a great idea whether you live in the suburbs or the city. One of the appealing aspects of this type of project is that you can complete it in an afternoon. All you need are the right tools and a little know-how.


Measure your window sill to determine the length of the box. Personal preference dictates whether you want the box to be the same length of the box of if you’d like it a bit smaller. Then, think about depth and width. For example, perhaps you’d like a box that is three and a half inches deep and three and a half inches wide. Write down the dimensions of your box.

Once the measurements are complete, gather materials to cut and build the box. Generally, one-by-fours work well for window boxes and they are available in eight-foot lengths, so you shouldn’t need more than a board or two to get the job done. Pressure-treated pine or cedar are typically preferred, but cedar is often more expensive.

You are going to cut your lumber into five pieces: two ends, a front panel, a back panel and a bottom panel. Cut the two ends first, then attach the other panels to them, using at least two nails per panel, per end. You can use a hammer for this, but a pneumatic nail gun will save time. Because one-by-fours are thin, there’s less likelihood of damage if you use a nail gun. When cutting your lumber, consider a miter saw, as this tool is perfect for making repeated and precise cuts.

Even if you’re using pressure-treated lumber, you’ll still want to seal it. A semitransparent water-based primer/sealer is optimal. This type of primer/sealer, while slightly less protective than a semi-solid or solid water seal, doesn’t effect the color of paint you may decide to apply later.

Also, if you’re not planning to use a planter in your box, cut drainage holes in the bottom panel prior to assembly. A 1/2-inch spade bit is perfect for knocking out holes like this.

Other tools and materials you’ll need include galvanized finishing nails (4M, 3-1/4″), a drill with a 3/8″ auger or masonry bit, a measuring tape, two 3/8″ bolts and washers, a stud finder, a level, a carpenter’s pencil and water sealant. Wood chisels, sanders or other woodworking tools are good to have on hand.


The best way to mount a window box is to either attach it your home’s wall studs or masonry work.

Attaching to studs

In most residential construction, wall studs are 16 inches apart from the center of one stud to the next. Using your stud finder, verify the location of the studs to precisely position your window box. Mark these areas with your carpenter’s pencil on both the outside of your home and the inside of your finished window box. Use your auger bit to drill holes into the studs, as well as the window box, in these locations.

Attach the box with the 3/8-inch bolts. A note of caution: Make sure the box is level before doing any final tightening.

Attaching to brick, stone or stucco

If your home’s exterior has any sort of masonry work, you’ll repeat the process outlined above. The main difference is that you won’t have to locate studs because the window box will be anchored to the brick or stonework.

As for your marks, make sure they are level and the same distance apart on your exterior wall and inside your window box.


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