Cold Frame
Credit: personal photo

Building a Cold Frame Step by Step

This article will tell you how to build a simple cold frame using plywood and some bits of lumber you can get from your local stores.  The material list below and the instructions are for a 4 x 3.5 ft cold frame.


Materials for the Cold Frame

  • 1-4x4 sheet of 1/2 inch plywood
  • 2- 2x2 8 ft furring strips
  • Box of 1.5 inch screws
  • 1- 1x8x4 piece of lumber

Assembling the Cold Frame

The first step in building the frame is to cut down the 4x4 sheet of plywood into the back and side panels of the cold frame. You can do this by following the diagram below to aid you in laying out and measuring you cuts.


Cold Frame Diagram

Take the 4x4 sheet of plywood and measure up 16 inches from the lower right corner and mark it.

Then measure 3.5 feet from edge to the inside of the sheet and mark it.

Measure up 8 inches from bottom of the plywood at your 3.5 ft mark and draw a line to 8 inches.

Then take a straight edge and draw a line from your 16 inch mark to your 8 inch mark.

Cut out the first side panel and repeat measurements as indicated on diagram to get second panel.

Assuming you have cut out the sides correctly you should be left with a 2x4 ft plywood panel you your can now trim down to 16 inches by 4 feet and that will form the back of your cold frame.

Now that you have the panels cut you need to take your 2 x 2 furring strips and cut them down to appropriate lengths to provide support for your panels.  You will need 2 x 2 strips in the following lengths,

  • 2 at 16 inches
  • 2 at 8 inches

Theses sections will be placed in the 4 corners of the box and are what you screw the plywood panels and 1x8 board into.  Once you have all the panels assembled you should have a box sitting on the ground in front of you.

Some reinforcement is still needed however to make it a little more durable.  You do this by measuring and cutting sections of 2 x 2 to fit at the top of the back panel and on the two side panels between the corner braces.  Once you have screwed them in place you will find the box to be much sturdier.  You may also have to put some angle braces in the front of the box.  You do this in the following way.Angle BracingCredit: personal photo

  1. Take what remains of the 2 x 2 and cut it in half
  2. Cut the ends of both pieces at a 45 degree angle.
  3. Screw into the panels





 At this point you should have a 4 by 3.5 foot cold frame box built and reinforced ready to use .  The next step is to create the cover with your choice of glazing.  Now most of the time the size of the glazing determines the size of the cold frame.  You can get around this by using large plastic sheeting that performs the same job as glass but much cheaper. 

 Materials for the Lid

  • 2-2x2 furring strips or 2x3 boards
  • box of 2.5 inch screws
  • 5x5 plastic sheeting 2 mil or thicker
  • 2 hinges

Assembling the Cover

The cover is simple box built from your choice of lumber size.  In my build I used 2x3 boards as that is what I had on hand.  Lid Diagram

  1. Take your wood and cut 2 4 foot sections and set aside.
  2. Then cut 2 39 inch sections and place with your 4 foot pieces
  3. Assemble the pieces using the 2.5 inch screw
  4. Attach hinges to lid at an equal spacing from the ends.
  5. Attach plastic sheeting and cut away the excess material.


Attaching the plastic can be done in a variety of ways.   One excellent method is to sandwich the plastic between two layers of wood which creates many contact points for holding the plastic. This method prevents tearing and when done correctly can give you a really tight layer of plastic which is great for shedding water. 

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A great source for further info on cold frames and other season extension ideas.