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Cedar and Metal Window Box

Mix a smooth metal surface with the warmth of cedar to make this DIY window box. Follow our simple plans and instructions, or customize the size to fit your home.

Cedar window box with metal trim installed on a house.

Project Overview

Skill Level


Estimated Time

1 day

Estimated Cost


Tools & Materials


  • Measuring tape
  • Miter saw or miter box and handsaw
  • Tablesaw, portable circular saw and straightedge, or jigsaw and combination square
  • Electric drill/driver, bits, countersink, driver bit
  • Clamps
  • Utility knife
  • Hammer and common framing nail
  • Level
  • Work gloves
  • 120-grit sandpaper and sanding block


  • See Project Diagram for materials required
  • Aluminum flashing, 10-in x 10-ft roll
  • 3 - 6-in angle braces
  • 2-in deck screws
  • #8 x 1/2-in washer-head screws
  • #10 x 2-in flathead stainless-steel sheet-metal screws
  • #10 x 3/4-in stainless-steel sheet-metal screws

Items may be Special Order in some stores. Product costs, availability, and item numbers may vary online or by market. Paint colors may vary slightly from those shown. Availability varies by market for lumber species and sizes.

Missing anything? Shop Online


Build the Box

Step 1

Cut the back (A) and slats (B) to length (Project Diagram, Cutting List, and Cutting Diagram). To make assembly easier, cut one extra slat to use as a support.

Good to Know

Cedar sawdust can irritate your eyes and throat. When you cut or sand cedar, wear breathing and eye protection.

Step 2

Screw bottom slats to the window box back.

Support the back (A) with two unfastened slats (B), drill countersunk pilot holes and screw slats one at a time into the back. Position the bottom faces of the slats flush with the bottom edge of the back and the end slats 5/8-inch in from each end of the back. Leave 5/8-inch spaces between slats. (Project Diagram, Drawing 1). The extra slat you cut supports the assembly as you fasten the last slat.

Step 3

For the sides (C) and front (D), rip a 1 x 12 to 10-1/8 inches wide. If you don’t have a table saw, use a portable circular saw and a straightedge or a jigsaw. To use a circular saw, mark the 10-1/8-inch width at each end and the center of the 1 x 12. With the saw unplugged, measure from the inside edge of the saw blade to the edge of the saw base on the motor side. Mark this offset distance from each 10-1/8-inch width mark. Align a straightedge with the marked offsets and clamp it in place. Adjust your saw to cut 1 inch deep. Lay the 1 x 12 with clamped straightedge across three pieces of scrap 2 x 4s on the floor—one supporting each end and one in the middle. Plug in the saw and keep the saw base against the straightedge as you cut. 


To use a jigsaw, draw a cutline 10-1/8-inches from one edge of the 1 x 12 using a combination square as a marking guide. Install a fine-tooth wood-cutting blade in your jigsaw and carefully cut along the line. Smooth the cut edge with sandpaper and a sanding block.

Step 4

From the ripped 1 x 12, cut the sides (C) to length (Project Diagram, Cutting List). Measure the distance from the top face of a slat (B) to the top edge of the back (A) and trim the extra slat to this length. Place the back/slats assembly (A/B) upside down on a flat surface and prop it upright with the trimmed slat. Position the back ends of the sides flush with the back face of the back (A). Drill countersunk pilot holes through the sides and fasten them to the back with 2-inch deck screws (Project Diagram, Drawing 1).

Good to Know

Where the screw holes are very close to the ends of the parts, drilling countersunk pilot holes prevents splitting when driving the screws. When drilling the pilot holes, only drill through the sides (C) and not into the ends of the back (A). The screws will drive easily into the end grain of the back without a pilot hole and will hold more securely.

Step 5

Screw the window box sides to the back.

From the remaining ripped 1 x 12, cut the front (D) to length (Project Diagram, Cutting List). Slip the front between the sides (C). With the top and bottom edges of the front and sides flush, drill countersunk pilot holes and screw the sides to the front. Then drill countersunk pilot holes through the front and screw the front to the slats (Project Diagram, Drawing 1).

Attach the Metal Trim

Step 1

Punch holes in the window box aluminum trim with a nail and hammer.

With tin snips or a utility knife, cut a 72-inch-long piece of 10-inch-wide aluminum flashing for the metal cover (E) (Project Diagram, Cutting List). (The flashing is longer than needed and you’ll trim it to exact length later.) Position the box assembly with the front (D) facing up. Center the length and width of the metal cover on the front and clamp it in place. Mark hole centers 1 inch apart for washer-head screws on the metal cover (Project Diagram, Drawing 1). Using a common framing nail, punch holes in the cover.

Step 2

Screw aluminum flashing trim to the window box.

Starting at a low setting, progressively adjust the clutch on your drill/driver so it slips just after the washer-head screws are fully seated. Drive a screw at each punched hole. The washer-head screws securely fasten the metal cover and give the completed window box an attractive riveted appearance.

Good to Know

Use a low clutch setting on your drill/driver, even if you have to finish driving the washer-head screws by hand with a screwdriver. The screws are short and will easily “spin out” in the soft cedar if over-driven.

Step 3

With the front of the metal cover secured, fold the flashing at the front corners of the box, letting the extra length protrude beyond the back. Mark screw-hole centers, punch holes and fasten the cover to the sides (C) with more washer-head screws (Project Diagram, Drawing 1).

Step 4

Trim the flashing to fit the window box sides.

Position the window box on one end, placing wood scraps underneath it. With one wood scrap backing the cut, use the end of the side (C) as a guide and score the metal cover with a utility knife. Make several light passes to cut all the way through the cover or, after a couple scoring passes, simply bend the cover back and forth until it breaks. Repeat at the other end. Smooth the sharp ends of the cover with sandpaper and a sanding block.


Always be safe and wear work gloves. Utility-knife blades are razor-sharp.

Mount the Window Box

Step 1

Position one 6-inch angle brace on the wall of your house centered under the window. The top of the protruding brace leg should be 8 inches below the window sill. Using the holes in the brace as guides, drill pilot holes and screw the brace to the wall (Project Diagram, Drawing 2). Use a level to position the other two braces, centered 15-3/4 inches on either side of the first brace (Project Diagram, Drawing 1). Drill pilot holes and screw them in place.

Step 2

Place the completed window box on the braces, centering it under the window. Using the holes in the braces as guides, drill pilot holes into the center and end slats (B) and secure the box with screws (Project Diagram, Drawing 2).

Step 3

Place plants in individual flower pots in the window box or drop in a rectangular plastic tray, fill it with potting soil and plant flowers in the soil.

In addition to adding a distinctive touch to this window box, the aluminum trim helps protect the cedar box from sun damage. Shop Lowe’s for additional outdoor accessories:

Plants and Planters 

Garden Decor



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