The walls of a greenhouse must maximize sunlight transmission for photosynthesis while creating a stable, protected environment by minimizing heat loss. The choice of wall material directly influences the internal climate, structural requirements, and long-term operating cost. Selecting the appropriate material is a fundamental decision that dictates the success of cultivating plants within the controlled conditions of a greenhouse structure. Different materials offer trade-offs regarding light quality, insulation, and durability, meaning the ideal solution depends on the grower’s specific goals and geographical location.
Glass: The Traditional Standard
Glass remains a traditional and highly valued material for greenhouse walls, prized for its exceptional light transmission, often allowing 90% or more of visible light to pass through. This clarity is beneficial for crops that require intense light exposure, and the material’s optical properties remain stable over decades. Standard float glass is the most economical type, but it offers poor insulation, leading to higher heating costs in cooler climates, and shatters into dangerous shards upon impact.
For improved safety, tempered glass is often used; it is heat-treated to be up to four times stronger than float glass and breaks into small, dull fragments. Horticultural glass is a traditional, single-pane option that is often overlapped, which is cost-effective but leads to significant air leaks and heat loss.
Double-paned insulated glass units sandwich an air or inert gas space between two panes, offering superior thermal performance. However, these units come at a higher initial cost and require a robust frame to support the added weight. Glass also possesses a high thermal mass, meaning it absorbs and slowly releases heat, which helps moderate temperature swings inside the structure.
Polycarbonate and Acrylic Panels
Polycarbonate (PC) and acrylic (PMMA) are modern rigid panel options, offering advantages over glass in weight and durability. Polycarbonate is valued for its impact resistance, offering up to 200 times the resistance of glass, making it suitable for areas prone to severe weather or hail. It is most effective in its multi-wall configuration (e.g., twin-wall or triple-wall), where internal air channels increase insulation and provide a higher R-value than single-pane glass.
Multi-wall polycarbonate sheets diffuse light as it passes through the internal structure, scattering sunlight evenly throughout the greenhouse. This diffusion helps prevent scorching, reduces hot spots, and increases the efficiency of photosynthesis by ensuring light reaches lower leaves.
Polycarbonate requires a specialized UV-protective coating to prevent the material from yellowing and degrading, maintaining light transmission properties for its expected lifespan of 10 to 15 years. Acrylic panels offer greater clarity than polycarbonate, with light transmission rates reaching 92%. However, acrylic is more expensive and more brittle, possessing only 10 to 20 times the impact resistance of glass before cracking.
Flexible Plastic Film Coverings
Flexible plastic film coverings, primarily made from polyethylene (PE), are the most cost-effective initial option, widely used for hoop houses and low-cost structures. The standard thickness is 6-mil film (one-thousandth of an inch), chosen for its balance of strength and light transmission. These films must be UV-stabilized during production to prevent them from becoming brittle, yellowing, and cracking.
A standard 6-mil UV-rated film typically lasts between four and six years before requiring replacement, representing a recurring labor and material cost. Specialized films include additives like anti-condensate treatments or infrared (IR) retention properties to help trap heat at night.
To improve insulation, two layers of film can be inflated with air to create an insulating air cushion, significantly boosting thermal performance. While light transmission is generally high (80% to 90%), the film’s structural instability means it must be kept taut to prevent damage from wind and wear.
Choosing the Right Material
The decision on the greenhouse wall material depends on balancing initial cost, insulation needs, and expected lifespan against the necessary light quality for the intended crops. Glass offers the highest light transmission and clarity but is the most expensive initially, requires the most substantial framing, and provides the lowest insulation value. Its lifespan can be decades long, but the high weight increases installation complexity.
Polycarbonate panels represent a moderate initial cost, offering superior insulation and durability, with an expected lifespan of 10 to 15 years. The lighter weight and high impact resistance reduce the required framing strength and long-term maintenance compared to glass.
Flexible plastic film is the lowest initial cost option but has the shortest lifespan, necessitating replacement every four to six years. It offers the lowest insulation unless a double-layer inflated system is used. Growers in cold climates benefit most from multi-wall polycarbonate, which reduces heating costs, while those in mild climates focused on high-light-demand crops may prioritize the clarity and longevity of glass.