Build a DIY cold frame using an old window

One of the projects that I knew I wanted to include in my book, Raised Bed Revolution, was a cold frame. I had seen some neat DIY cold frame examples through garden visits over the years, great cold frame kits through various retailers and innovative cold frames that used old windows as the lid. I was also inspired by Niki, who gardens 365 days a year (you can find some of her cold frame tips here).

When the photographer for my book, Donna Griffith, grabbed an old window a mutual friend was giving away, I enlisted my brother-in-law, Deon, to help me figure out how to build a cold frame to fit.

You could also use clear plastic for the lid. The idea is that the glass or plastic will harness the winter sun’s warmth, allowing plants to grow inside. Now we’re not talking tomatoes here, but there are several things you can grow, including root vegetables and greens. One thing I read about cold frame designs is that the back should be about three to six inches higher than the front, which helps capture as much solar energy as possible.

Here are the steps for my DIY cold frame

You can adjust measurements based on the size of the lid you want to use. One thing to note is ensuring that the window does not have lead paint on it as you don’t it to flake off in the soil over time.

Tools

• Miter saw
• Circular saw or jigsaw
• Japanese dozuki saw
• Orbital sander or sandpaper
• Power drill or impact driver
• Straight edge and pencil
• Clamps (optional)
• Tape measure
• Eye and ear protection
• Work gloves

Materials
Note: This project was made to accommodate an old window that’s 32 1⁄4″ long × 30″ wide.

• (4) 1 1/2″ × 6″ × 8′ cedar boards
• (2) hinges
• 2 3⁄4″ screws

Cut list

• (5) front and back pieces measuring 1 1/2 × 6 × 32 1⁄4″
• (4) side pieces measuring 1 1/2 × 6 × 30″
• (2) angled side pieces (see instructions) measuring 1 1⁄2 × 5 1⁄2 × 30″
• (2) corner braces (cut from scrap) measuring 1 1⁄2 × 6 × 16 1⁄2″
• (2) corner braces (cut from scrap) measuring 1 1⁄2 × 6 × 11″

Step 1: Build the frame

Lay out the 32 1⁄4-inch front and back pieces so that they cover the sides of the 30-inch side pieces to form a box. Screw in place to make the bottom of the frame. Repeat this step to create the second layer. For the third layer, there is a back piece but no front piece because of the angled slope you want to create once the window is attached. This means the side pieces need to be cut at an angle. They also need to be longer to accommodate the slope. Leave about 10 inches on the end in order to either screw or clamp the work piece down to your bench for when you make the cut. Screw the side piece to the back piece temporarily, and place on top of the box. Take a straight edge and place it from the edge of the top corner to the front of the box diagonally across the board and draw a line. Remove the temporary screws and attach the extra 10-inch length to your work table with clamps or screws. Use a circular saw or jigsaw to slowly cut it out as you’re going across the grain. One cut gives you both angled side pieces. Trim the extra 10 inches off the one piece to length.

Step 2: Sand the side pieces

Use an orbital sander or sandpaper to smooth the rough edges of the angled side pieces.

Step 3: Attach the angled side pieces

Place the two angled side pieces inside the edges of the third back piece and fasten in place from the back. There is no front piece for the third level of this assembly because of the angle of the final project. Add an extra screw on each side toward the front to secure the side pieces in place because they will not attach to the corner braces.

Step 4: Install the corner braces

From one of the remaining cedar boards, cut two pieces that are 2 × 16 1⁄2 inches and two pieces that are 2 × 11 inches. The long pieces are the braces for the back corners. Cut the ends of these on a slight angle to accommodate the gentle slope of the tops of the angled side pieces, or you can cut a bit shorter and install them below the angle. The window should close without leaving a gap further down. From the inside, screw these four braces to the outside frame to secure it in place.

Step 5: Trim the front

If there is a bit of wood from the two angled pieces overlapping the front, use a dozuki handsaw or the orbital sander to gently trim it away.

Step 6: Attach the hinges

The preexisting metal piece along the back of the old window would have prevented the screws for the hinges from going in, so two scrap pieces of wood were trimmed and used to create a new “back” to which the hinges could be attached. This also pushed the window forward a bit to make up for the extra centimeters that were added from the diagonal. Once these scraps are screwed in place, attach the two hinges to the window frame and the frame of the box.

Once you start using your cold frame, it’s important to know that things can get a little too heated inside, so it’s important to vent the cold frame sometimes, even in the winter. I just use an old piece of wood to prop mine open, but you can also get automatic vent openers that will gauge the temperature and open accordingly.

Project designed by Deon Haupt and Tara Nolan
All photography by Donna Griffith
Technical illustration by Len Churchill
Excerpted with permission from Cool Springs Press

For more on cold frame gardening, check out these posts: 

• Learn how to grow in a cold frame
• Tips for successful cold frame growing
• Get a jump start on spring with a cold frame
• Cold-hardy crops for fall and winter gardens