Garden Construction Coach on How to Build a Cold FrameMarch 08, 2009
The most expensive part of the cold frame is the glazing. For my project I just used acrylic glazing purchased at my local home store, but you could also use old windows, glass panels or polycarbonate greenhouse panels.
Along with some kind of glazing, all you need for this cold frame is a sheet of 1/2″ plywood, 3 – 2x6x10s, 2 – 2x2x8s, 3″ corner brackets, 5″ T-hinges, plenty of 2 1/2″ #8 wood screws, and some 3/4″ #6 Round head screws.
I started by cutting the plywood. You need two pieces that will form the sides. First, I turned the plywood on it’s long edge and cut a section off that is 37 1/2″. This piece is plenty to get the two sides.
Since the width of the cold frame is 37 1/2″, I measure up 11 1/2 inches on one side and then 23 inches on the other. I drew a line from each point to mark my angle cut. I did the same thing from the other side of the cut piece. Now you have your two sides of the frame.
Next, I took the 2x6x10s and cut them in 1/2 giving me 6 5 foot pieces. 2 of these will be the front and 4 of them will be the back. I line up one of the 2×6 with the front or short end of a plywood side and screw them together with the #8 wood screws. Then I did the same on the other side. I repeat this stacking one more 2×6 in the front and a total of 4 for the back. Now we have the main box.
To strengthen everything I cut two pieces of 2x2s that will run on the inside of the plywood at the base. Then cut another set that will run along the inside of the plywood on the top edge. These pieces not only strengthen things, but will also give the lids a place to rest on.
With the main cold frame done, I cut the 2x2s for the two lids. Each lid is long enough to go from the top of the back wall to the front about 39 inches and is also about half the width of the cold frame, just under 30 inches. Each corner of the lid frame is connected with the 3 inch corner brackets.
Next, I cut the acrylic glazing to size of the frame. I made it about 1/4 inch shorter and thiner then the frame. The pieces are attached with the #6 wood screws and it is best to pre drill the holes through the glazing. The Rounded head screws will hold the glazing now and snug to the frame.
Next I attached the lids to the back with the T hinges. First i put both lids on the cold frame and positioned them between the sides so the could each open individually. then I attached the T-hinges to the back of the cold frame and then the back of the lid.
The cold frame is basically done. The last thing I did was get some perforated straps from my local hardware store to help hold up the lids for venting. Attached a screw to the front of each lid in the center and allow it to stick out 3/8th of an inch. Then half way down the top front 2.×6 in line with the screw in the lid I attached a L-hook. Hook one end of the strap to the L-hook. To prop up the lid, open it and connect on hole on the other end of the strap around the screw in the lid.