"twist drill bitUsing a cold frame can extend your growing season four to six weeks on each end. Here is a good model that is straightforward to build, small enough to reach into easily yet large enough to help in your gardening, and a great use for any spare window sashes you may have on hand.
MATERIALS
Lumber
2"×4" cedar (10' length)
1"×6" cedar (12' length and 16' length)
1"×8" cedar (6' length)
1"×10" cedar (8' length)
Two tomato stakes (27" lengths)
Two 30"×29" window sashes
Supplies
Two pairs of 3½"×2½" exterior hinges and screws to go with them
2" exterior wood screws (70 or so)
Two 1⅝" exterior wood screws
Tools
Tape measure
Pencil
Carpenter’s square
Wood saw
Power drill
"twist drill bit
Driver bit to match screws
Temperature
With a cold frame, the danger of heat and dehydration is far greater than the danger of cold, even during the early spring and late fall when you will be using your cold frame the most. Remember that even on the coldest winter day, the bright sun can quickly push the temperature in the cold frame up to above 75°–80°F (24°–27°C), which should be the maximum. Provide a system of props so that, if there is a chance of overheating, the sash can be raised. Unless prevailing winds blow directly into the cold frame, there is little danger of damaging plants through chilling them.
WINDOW SASH COLD FRAME. Old window sashes are ready-made tops for this style of cold frame. If you don’t have any spare sashes, you can frequently find overstock for sale at your local lumber store.
Cutting the lumber. From the 2"×4", cut three 19½" lengths 
and three 12½" lengths 
for the upright posts.
From the 1"×6", cut three 59½" lengths for the lower front and back boards 
and five 25½" lengths for the side and center boards 
.
From the 1"×8", cut one 59½" length for the upper front 
.
From the 1"×10", cut boards for the upper back 
and angled upper sides 
as specified in the cutting diagram at right.
Cutting diagram
BUILDER’S TIP
The dimensions for this style of cold frame revolve around the window sashes you use. If yours are a different size than the 30"×29" ones specified here, you’ll have to modify the frame accordingly. Either way, attaching the sashes with hinges that have loose pins will allow you to remove the windows easily if needed.
Constructing the cold frame. To start, build the side panels using the taller upright posts for the back corners and the shorter upright posts for the front corners. The angled upper sides will create a sloped top that both permits rainfall to run off the cold frame and allows for maximum sunlight to reach the plants inside. Screw the front boards & and back boards & to the ends of the side boards & to create a box. Then attach the center posts & to the inner box and screw the ends of the center board to them.
Position the window sashes on the frame so that the tops are flush with the back wall (they will overhang the sides and front of the frame a bit), and mount the hinges. To provide ventilation, use the 1⅝" screws to attach the bottoms of the tomato stakes to the inner front corners of the frame, as shown. The screws should be loose enough to allow the sticks to pivot forward when you want to prop the frame open.
FIG. 1
