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How to Build Window Treatments

How to Build a Windowsill Shelf

Remove the apron under the old windowsill and cut the sill off flush with the wall surface (left). Butt the new shelf, as wide as 12 inches, against the cut edge (right); brace it with wood brackets and a 1 × 4 apron.

A windowsill shelf is a handy place for plants, canisters, jars or any display items you have collected, and it can be placed on the inside or outside of a window. Building a windowsill shelf is an easy way to add interest and additional storage without taking up extra space.


  • pry bar
  • hammer
  • measuring rule
  • pencil
  • handsaw or power saw
  • if required, saber saw
  • plane
  • carpenters' square
  • nail set
  • paintbrush


  • 1 × 6, 1 × 8, 1 × 10, or 1 × 12 pine stock
  • carpenters' glue
  • 6-penny and 10-penny finishing nails
  • 1 × 4 pine stock
  • matching paint or stain

Time: about 2 hours


The way you'll build your windowsill shelf depends on the window's construction. First, determine how to fit the shelf into the window's trimwork. Some, and possibly most, of the trimwork will likely have to be removed so you can cut it.

With a pry bar, pry off the apron below the windowsill. Remove the windowsill; you'll probably have to remove the side jamb trim and the side casing. Remove all trimwork carefully; make sure you don't damage it.

Measure and mark the sill so you can cut its inside edge -- the edge facing the room -- flush with the surface of the wall; cut the sill as marked and plane the cut edge smooth and square. Replace the sill.

To make the windowsill shelf, use 1 × 6, 1 × 8, 1 × 10, or 1 × 12 pine stock. The shelf can be as wide as 12 inches and as long as the window is wide or longer -- extending beyond the sides of the window. If the shelf extends beyond the sides, make it long enough to span a wall stud on either side, as the shelf braces will be secured to these studs.

You can leave the ends of the shelf square, or round or angle them as desired. Measure, mark, and cut the shelf to the length and configuration desired, using a saber saw to curve the edges, if necessary. Set the edge of the shelf against the sill and the wall to check it for a tight fit. Plane and smooth the edge as necessary.

Measure the side pieces of the window frame to butt tightly against the top of the shelf, and trim them as necessary. Replace the side pieces and the side jambs in the window frame. Apply carpenters' glue to the bottom ends of the side pieces and to the edge of the shelf where it joins the sill and the window framework. Place the shelf into position and drive 6-penny finishing nails up through the shelf and into the ends of the side pieces to secure it. Countersink the nails with a nail set.

Next, install the shelf brackets. Attach the brackets solidly to the wall studs on both sides of the window and to the shelf, using 10-penny finishing nails. Countersink the nails.

Cut a piece of 1 × 4 pine stock for a new apron below the shelf. Fit the piece of 1 × 4 beneath the shelf to serve as additional support and to hide the exposed rough opening of the window. Nail the 1 × 4 in place with 10-penny finishing nails. Countersink the nails.

Finally, finish the shelf and the new trimwork to match the window trim.

After you've built a windowsill shelf, try building a whole set of window shelves for plants. See the next page for details.

For more ideas on window-related projects, see:

  • How to Repair Windows: Get the tips and instructions you need to correct common problems and keep your windows in good working order.
  • How to Clean Windows: Dirty windows are a big detraction, so follow these directions to keep your glass panes shiny and clear.
  • Kitchen Window Treatments: The kitchen is often the center of a home, so windows there need a special look. Choose the perfect treatment for a warm and welcoming atmosphere.