How to Build a Cold Frame

Use rot-resistant planks and a salvaged window to build a protective box that extends the growing season

Photo by Matthew Benson

Not all gardeners have the luck to live in temperate climes. Instead of battling frost, install a cold frame to protect your plants like a mini greenhouse. Its natural warmth lets you foster seedlings in early spring and keep veggies going through fall and even into winter. This Old House senior technical editor Mark Powers shows how to build the box from rot-resistant wood and a salvaged window. Once it's finished, choose a south-facing spot in your yard where water won't pool, and enjoy all that extra gardening time.


Steps // How to Build a Cold Frame
1 ×

Overview for Building a Cold Frame

 
Step One // How to Build a Cold Frame

Overview for Building a Cold Frame

illustrated exploded view of a cold frame
Illustration by Gregory Nemec

Project timeline:

Friday: Size and cut the pieces.

Saturday: Assemble the frame and attach the window.

Sunday: Prepare the site and install the cold frame.

 
2 ×

Measure the Window

 
Step Two // How to Build a Cold Frame

Measure the Window

measuring a window for a cold frame
Photo by Matthew Benson

The window lid will be hinged along its length and sloped to let in maximum sunlight. Measure the window's long edge to get the length for the front piece and the two back pieces. Sandwiched between, the sides taper back to front, which means they'll be shorter than the window is wide. To determine their length without resorting to geometry, stage one end of the frame two-dimensionally: Butt two boards end-to-end, then pair up a third parallel with one of them to mimic the height of the back. Slide the single board away from the pair and open a gap approximately as wide as the window. Then stand the window on end, angling it from the "back" to the "front," and adjust the gap until the window just overlaps the boards at either side, as shown. Now measure the gap to determine the length of each side piece.

 
3 ×

Cut the Pieces to Length

 
Step Three // How to Build a Cold Frame

Cut the Pieces to Length

cutting wood with a miter saw
Photo by Matthew Benson

Using a miter saw, cut to length the front board, two back boards, and four side boards.

 
4 ×

Mark the Angle

 
Step Four // How to Build a Cold Frame

Mark the Angle

marking an angle onto a board with a straightedge
Photo by Matthew Benson

The top board of each side needs to be tapered. To get that angle, run a straightedge diagonally from the top corner of one end of a board to the bottom corner of the other end, and mark the line, as shown.

 
5 ×

Cut the Angle

 
Step Five // How to Build a Cold Frame

Cut the Angle

cutting a board at an angle with a jigsaw
Photo by Matthew Benson

Clamp the board to the work surface and use a jigsaw to cut the angle. Now you have your two tapered pieces.

 
6 ×

Mark and Cut the Tall Battens

 
Step Six // How to Build a Cold Frame

Mark and Cut the Tall Battens

marking a cut line on board with a pencil
Photo by Matthew Benson

The tops of all the frame's battens must follow the side taper so that the lid can close. For the tall ones at the rear of the sides, cheat them in using a board on edge to block out space for a back batten. With the tall batten flush at the bottom, transfer the taper angle to the board, as shown. Using the miter saw, cut that angle. Repeat.

 
7 ×

Mark and Cut the Short Battens

 
Step Seven // How to Build a Cold Frame

Mark and Cut the Short Battens

marking a cut line on board with a pencil
Photo by Matthew Benson

Cut two more battens at the same angle. Since they taper down to a single board in front, you can mark each batten's height with the width of a board, as shown. Cut both battens.

 
8 ×

Glue the Battens

 
Step Eight // How to Build a Cold Frame

Glue the Battens

applying construction adhesive to boards
Photo by Matthew Benson

Using construction adhesive, glue the battens in place, making sure to leave space for the back batten.

 
9 ×

Screw the Battens

 
Step Nine // How to Build a Cold Frame

Screw the Battens

screwing boards and battens together with a drill/driver
Photo by Matthew Benson

Using a drill/driver and four 1⅝-inch screws, secure each batten.

 
10 ×

Cut the Back Battens

 
Step Ten // How to Build a Cold Frame

Cut the Back Battens

cutting a bevel in the battens with a jigsaw
Photo by Matthew Benson

The battens binding the back boards together must be beveled at the top to match the side taper. Using the miter saw, cut a scrap block to the angle of the taper. Then loosen the jigsaw footplate, hold it flat against the side edge, tilt the blade to match the taper, and set the saw, as shown. Cut the bevel. Now cut the batten to length so that it's flush with the frame height from the peak of the bevel to the bottom of the board. Repeat for a second batten.

Tip: If the plants you want to grow are taller than what would fit in this frame, you can make your version higher by adding a plank to each side and sizing the battens accordingly.

 
11 ×

Position the Back Battens

 
Step Eleven // How to Build a Cold Frame

Position the Back Battens

positioning the batten on the edge of the board with a spacer
Photo by Matthew Benson

To allow room to sandwich the sides between the front and back of the frame, set a board on edge as a spacer, flush with one end of the back. Position the batten against the spacer, flush at the top and bottom.

 
12 ×

Glue and Screw the Back Battens

 
Step Twelve // How to Build a Cold Frame

Glue and Screw the Back Battens

screwing in the back battens with a drill/driver
Photo by Matthew Benson

Using a caulk gun and construction adhesive, glue each batten in place. Then sink four 1⅝-inch screws through the battens and into the back boards.

 
13 ×

Screw the Four Sides Together

 
Step Thirteen // How to Build a Cold Frame

Screw the Four Sides Together

screwing the frame together with a drill/driver
Photo by Matthew Benson

Butt a side assembly into the back to form a corner. Drill a countersink, and drive two 2½-inch screws through the side and into the edge of the back batten, as shown. Repeat for the second side. Attach the front board with two screws through its ends and into the edge of the short battens.

 
14 ×

Attach the Hinges

 
Step Fourteen // How to Build a Cold Frame

Attach the Hinges

screwing the hinges to the frame with a drill/driver
Photo by Matthew Benson

Screw removable-pin hinges into the battens on the inside corners. This lets you remove the assembly screws, take out the pins, and easily break down the frame for storage.

 
15 ×

Attach the Hinges

 
Step Fifteen // How to Build a Cold Frame

Attach the Hinges

raking the soil to create a level bed where the cold frame will be placed
Photo by Matthew Benson

Using a garden rake, loosen and turn the soil, creating a level bed for the frame.

 
16 ×

Install the Pavers

 
Step Sixteen // How to Build a Cold Frame

Install the Pavers

installing pavers around the the cold frame area as a stable foundation
Photo by Matthew Benson

Set the frame in place and lift each side to slip pavers beneath it to create a sturdy foundation. The bottom edge of the frame should rest on the center line of the pavers, as shown.

 
17 ×

Attach the Lid

 
Step Seventeen // How to Build a Cold Frame

Attach the Lid

fastening the lid to the cold frame with a drill/driver
Photo by Matthew Benson

Refurbish the window as necessary, coat it with an exterior paint, and let it dry. Set the window in place so that its edges are flush with the frame. Screw two strap hinges to the back edge of the window and the back of the frame, as shown.

 
18 ×

Install the Handle

 
Step Eighteen // How to Build a Cold Frame

Install the Handle

installing the handle to the cold frame lid with a drill/driver
Photo by Matthew Benson

Refurbish the window as necessary, coat it with an exterior paint, and let it dry. Set the window in place so that its edges are flush with the frame. Screw two strap hinges to the back edge of the window and the back of the frame, as shown.

 
19 ×

Cut the Vent Rods

 
Step Nineteen // How to Build a Cold Frame

Cut the Vent Rods

vent rod used to prop open the lid of the cold frame
Photo by Matthew Benson

Cut several pieces of ½-inch dowel at varying lengths. They can be used to prop up the window for ventilation or to keep plants from overheating on sunny days. This also prevents moisture buildup.

 
20 ×

Position the Frame

 
Step Twenty // How to Build a Cold Frame

Position the Frame

placing plants inside the cold frame
Photo by Matthew Benson

Set the assembled cold frame on its paver foundation. With the lid propped up, use a garden spade to dig holes for your seedlings or plants. Then watch them flourish regardless of outside temperatures.

 
 
 

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