Polycarbonate has become a popular glazing material for greenhouses, offering a lightweight and impact-resistant alternative to traditional glass. Choosing the correct thickness is the single most important decision affecting the structure’s performance and long-term operating cost. The optimal panel size must balance thermal efficiency, structural integrity, light transmission, and the initial investment. Understanding how thickness relates to these factors is necessary to create a successful, energy-efficient growing environment.
Polycarbonate Structure and Measurement
Polycarbonate sheeting used for greenhouses is categorized by its internal structure, which directly impacts its performance and measured thickness. The most common types are twin-wall and multi-wall panels. Twin-wall polycarbonate consists of two layers separated by internal ribs, creating a single insulating air gap. Multi-wall panels include three or more layers, resulting in multiple, smaller air pockets, which enhances insulation properties.
The thickness measurement, expressed in millimeters (mm), refers to the overall depth of the panel. For example, a 10mm twin-wall panel is 10mm deep, with the measurement encompassing both the plastic layers and the air space between them. This trapped air is the mechanism responsible for the material’s superior thermal performance compared to a solid sheet.
The Role of Thickness in Insulation
The primary reason to select a thicker polycarbonate panel is to improve the thermal performance of the greenhouse structure. Thicker panels, especially those that are multi-wall, trap more stagnant air, which significantly increases the material’s thermal resistance.
Thermal performance is measured using the R-value (resistance to heat flow) or the U-factor (rate of heat loss). A higher R-value or a lower U-factor indicates better insulation, meaning less heat escapes the greenhouse. For instance, a 4mm twin-wall panel might have an R-value of 1.43, while a 10mm panel can reach an R-value of up to 2.5. This improved heat retention directly translates to reduced energy consumption and lower heating costs during colder months. Choosing a thicker sheet can notably stabilize the interior temperature, protecting sensitive plants from sudden and extreme temperature fluctuations.
Balancing Durability, Light Transmission, and Cost
Beyond thermal performance, the thickness of a polycarbonate panel introduces trade-offs related to the material’s physical strength and its optical properties. Thicker panels offer greater rigidity and structural integrity, which is essential for resisting external forces. This enhanced durability allows the greenhouse to withstand heavy snow loads and high wind speeds common in severe weather zones. A thicker, multi-wall design is less prone to cracking or breaking under impact from hail or other debris.
An increase in thickness and the number of internal walls, however, slightly decreases the overall percentage of light transmitted. For example, while a 4mm twin-wall panel can transmit around 85% of light, a 10mm twin-wall panel typically transmits about 77%. This reduction should be considered, especially for plants that require high light levels or for greenhouses located in regions with low winter light. The multi-wall structure does diffuse the light more effectively, which helps prevent plant scorching and ensures light reaches the growing area evenly.
The material cost increases substantially with thickness and the complexity of the wall structure. Thicker, multi-wall panels are more expensive upfront due to the increased material used in their construction. This higher initial outlay must be weighed against potential long-term energy savings from superior insulation and the reduced risk of replacement due to storm damage. For many growers, the superior thermal efficiency and durability of thicker panels justify the added expense, particularly in climates requiring prolonged heating.
Specific Thickness Recommendations by Climate
The optimal polycarbonate thickness is determined by the climate conditions and operational goals.
Thickness Recommendations
For specific growing needs, the following thicknesses are recommended:
- 4mm or 6mm Twin-Wall: This is sufficient for seasonal greenhouses used only during mild spring and summer months, or in warm climates with no freezing temperatures. This thinner option offers maximum light transmission and is the most budget-friendly choice.
- 8mm Twin-Wall: Recommended for moderate climates with extended seasons that require light heating during early spring or late fall. This thickness provides a better balance of insulation and cost compared to thinner options.
- 10mm Multi-Wall: Recommended for year-round production in cold climates that experience significant freezing temperatures or heavy snow loads.
- 16mm or Thicker Multi-Wall: These panels provide the highest R-values and the greatest structural strength, making them the standard choice for maximum energy efficiency and protection in severe winter conditions.