Glass Greenhouse Vs Poly Greenhouse

Glass delivers higher light transmission and a twenty-five year service life at two to three times the capital cost of polyethylene film, which needs replacing every three to five years. Neither is universally correct. The decision turns on how light-limited your crop is, how cold your winters are, and how expensive your capital is.

Light is the primary yield driver in protected cultivation, and the common rule of thumb is that one percent more light produces roughly one percent more yield in light-limited conditions. Glass starts higher and, critically, degrades far less over time.

• Diffuse glass: 82 – 92% transmission, minimal degradation over life
• Single float glass: 88 – 90% when new
• New double-inflated film: 85 – 88%
• Film after three years: 70 – 78% as dust and UV degradation accumulate
• Twin-wall polycarbonate: 78 – 82%, gradual yellowing over time

Single glass and single film insulate similarly, which surprises many buyers. The real energy differences come from double glazing and from screens, not from the choice between glass and film as such. Double-inflated film actually outperforms single glass because the air gap does the work.

Film replacement is the line item most often omitted from comparison. Recovering a hectare costs both materials and labour, and it recurs. Over a twenty-year horizon a film structure will be re-covered four to six times, which substantially narrows the apparent capital advantage.

Glass wins where light is the binding constraint and the facility must produce year-round. For high-wire tomato or cucumber in a temperate or cold climate serving a winter market, the yield difference compounds every season and the longer life amortises the premium.

• Year-round high-wire vegetable production
• Temperate and cold climates with low winter light
• Facilities where supplemental lighting is installed
• Long investment horizons with access to cheaper capital

Film wins where the crop is less light-limited, the climate is mild, or capital is constrained. For strawberry and blueberry in mild climates, film captures most of the achievable yield at a fraction of the cost and typically shows a shorter payback.

• Soft fruit and berry production in mild climates
• Seasonal or shoulder-season production programmes
• Projects where payback period matters more than asset life
• Phased developments testing a market before committing capital

The correct comparison runs both options over the same horizon including re-covering cycles, energy consumption and yield difference. Run on that basis, glass and film often converge much more closely than the headline capital numbers suggest — and the winner flips depending on crop and climate rather than being fixed.