Polycarbonate provides a number of benefits as a construction material for greenhouses, including high light transmission, thermal insulation, and impact resistance. To ensure you get the right material to create optimum growing conditions in your greenhouse, it helps to have a basic understanding of how the structure, thickness, and color of the polycarbonate affects its light transmission and insulating properties before you buy. Here are a few tips for buying polycarbonate for greenhouses that will help you get the most out of the material.
Structure and thickness affect thermal insulation and light transmission.
Polycarbonate comes in both solid sheets and multiwall sheets. Multiwall sheets are typically the material of choice for greenhouses because they provide greater thermal insulation; however, the internal structure of multiwall sheets and the thickness of the material also impact light transmission. Multiwall is available in 2-wall, 3-wall, 4-wall, X, and honeycomb internal structures as shown below. Structures may be chosen to achieve a certain visual aesthetic, but they also come with different ratings for insulation and light transmission.
For greenhouses, light transmission of 80 to 90 percent is considered ideal for growing, though specific crops may have different light requirements. To achieve desired growing conditions, greenhouses are typically constructed of 2-wall polycarbonate because it offers a balance of light transmission and thermal insulation. Other structures, like 3-wall and honeycomb, fall in the 75 percent light transmission range, which may be sufficient for certain plant types or areas where the growing season is longer. Regardless, the general rule is that thicker material provides greater thermal insulation but less light transmission, and thinner material offers more light transmission and less insulation.
|Structure & Thickness||U-value||Light Transmission|
Insulating properties (U-value) and light transmission of 2-wall polycarbonate sheets.
The color of polycarbonate sheets also affects light transmission.
The standard color for greenhouse polycarbonate is clear, but you may be tempted to select one of the many other colors available to achieve a visual effect. As you may have guessed, adding color to polycarbonate also affects light transmission and is like putting a giant pair of sunglasses on your greenhouse. To understand the effect color has on light transmission, look at this chart comparing clear, opal, and bronze 2-wall, 4mm sheets and their respective light transmission rates.
Light transmission of clear, opal, and bronze 2-wall, 4mm polycarbonate sheets.
When scheduling delivery, remember you can’t store polycarbonate sheets in direct sunlight.
If you’re planning to have polycarbonate sheets delivered to a construction site, make sure you have a place to store them that is out of the sun until they’re ready to be installed. Polycarbonate sheets come with a protective film over the surface that should remain in place until sheets are installed and then be removed after installation. This protective film can bake on to the surface of the sheet if it’s exposed to the heat of direct sunlight, making it virtually impossible to remove.
Make sure you get a warranty and the manufacturer’s installation and care instructions.
The standard warranty for polycarbonate is ten years, but it will often last much longer than this if properly cared for and cleaned according to the manufacturer’s instructions. The manufacturer should also provide instructions for installing, cutting, drilling, and cold forming, and these specific instructions should be followed to promote the longest performance life.