Growing Area
18 sq ft
Glazing Sheets
2
Hinges
2
Total Growing Area
18 sq ft
Glazing Sheets
2
Frames
1
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Result
Area = 6 × 3 = 18 sq ft. Lid area = 18 sq ft. Polycarbonate sheets (16 sq ft each) = ceil(18/16) = 2.
Inputs
Result
Area = 4×4×2 = 32 sq ft. Lid area = 32 sq ft. Glass sheets (8 sq ft each) = ceil(32/8) = 4.
A standard cold frame is 3×6 ft (18 sq ft) for easy reach from one side. The back should be 18 inches tall and the front 12 inches for proper water runoff and sun angle. Wider frames (4 ft) need access from both sides.
Twin-wall polycarbonate is the best overall choice — it insulates better than glass, is shatterproof, and lasts 10+ years. Glass is heavier but provides slightly more light. Polyethylene film is cheapest but needs yearly replacement.
A cold frame raises temperatures 10–20°F above ambient during the day and 5–10°F at night. Double-glazed frames retain more heat. Adding thermal mass (water jugs) inside provides additional overnight warmth.
Use 2×6 or 2×12 cedar or pressure-treated lumber for the box sides. You need two long boards and two short boards per frame, plus 2×2 strips for the lid frame. Cedar lasts 10–15 years without treatment.
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Last Updated: Mar 19, 2026
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