Covering materials are one of the main components of any type of greenhouse construction — be it for home or commercial use — the covering materials are also called glazing.
Guide To Covering Materials
What you select for a greenhouse covering material depends ultimately on your budget, climate and what you plan to grow in the greenhouse.
Four main types of glazing
- Glass
- Polycarbonate
- Plastic Films (Polyethylene)
- Fibreglass
Each has its advantages and disadvantages. There is a variety of greenhouse covering materials that can be used to create a warm inviting greenhouse ecosystem. With the current explosion of interest from both commercial farmers and backyard gardeners, the options for materials are constantly expanding.
Glass Traditional “True Greenhouse”
For permanence, glass is the traditional preferred covering material. Its ability to last indefinitely, avoid falling into the urban legends about glass resilience. Glass is breakable and is more time-consuming, and dangerous to install. For glass installation, a much sturdier frame is required than plastics coverings.
Improvements with glass in recent years have seen increased strength (Double and Triple strength ratings) to resist breaking. This has allowed for the production of larger panes, and fewer structural members being required, allowing more light to enter the greenhouse. Also, bringing about increased thermal efficiency (R-Factor/U-Factor).
Other advances to bring down heat loss include DoubleWall tempered glass which reduces the loss of heat by about one-third. A low-emissive or low-E coating is yet another option, it reduces heat loss without a corresponding loss of essential plant light.
In addition to being energy-efficient low-E glass reduces condensation, partially blocks ultraviolet rays and makes the inside glass surface warmer to the touch.
Frosted and hammered panels can be used to break up the light rays for more even distribution.
Polycarbonate Panels and Rolls
Polycarbonate panels and rolls offer high durability and resistance to impact, this is why you will often find them used in more extreme climates where you find a high level of precipitation. Its primary disadvantage, opposite to polyethylene, is its higher cost.
Fibreglass Greenhouse Coverings
Fibreglass is another material frequently used in backyard greenhouse builds. Cheaper than polycarbonate and glass, fibreglass is often more expensive than polyethylene.
With fiberglasses rigid and very durable structure it doesn’t need the backing of glass from a structural perspective, this lessens the price somewhat, as well.
Fibreglass also holds up reasonably well to extreme weather damage, and for that reason has been used in places like Alberta where hail is a big issue.
The disadvantages of using fibreglass include its vulnerability to sun exposure. When exposed to long periods of sunlight, the fibres in the material tend to swell and reduce light transmission. Fibreglass may last as little as five years before the UV breakdown becomes significant.
Fibreglass is also quite combustible—equal, say wood—and flames will continue to ignite, even if you remove the ignition source. Many growers consider this safety issue a good reason not to use fibreglass.
Polyethylene Plastic Coverings
Polyethylene Panel Coverings
Polyethylene can also be made into a rigid panel or semi-flexible rolls, often with a twin wall construction with air space for insulation in between. Notably perfect for fitting greenhouses with shallow arches. UV protected and some are guaranteed to last 10 years.
Vinyl Greenhouse Coverings
Vinyl greenhouse covering materials are primarily used for a clear “showroom” quality look. Used only on the ends of greenhouses, give a nice clear view of your backyard greenhouse. Manufacturers advise against using vinyl to cover the top of the greenhouse.
Siding with clear vinyl is supposed to last about 4 years. We have no plans to employ vinyl, requiring a two material covering system, as it doesn't fit with Greenhouse Fanatics design goals.
Greenhouse Covering Material Comparison Table
| Greenhouse Covering | R-Factor | U-Factor |
|---|---|---|
| FiveWall Polycarbonate, 16mm | 3.20 | 0.31 |
| Double Pane Glass low E | 2.50 | 0.25 |
| TripleWall Polycarbonate, 16 mm | 2.50 | 0.40 |
| Double Pane Window Glass | 2.50 | 0.40 |
| 5mm Solexx Panels | 2.30 | 0.43 |
| 3.5mm Solexx Panels | 2.10 | 0.48 |
| TripleWall Poly-carbonate, 8mm | 2.00 | 0.50 |
| Double Pane Storm Windows | 2.00 | 0.50 |
| TwinWall Polycarbonate, 10mm | 1.89 | 0.53 |
| Acrylic TwinWall | 1.82 | 0.55 |
| TwinWall Polycarbonate, 8mm | 1.60 | 0.63 |
| TwinWall Polycarbonate, 6mm | 1.54 | 0.65 |
| TwinWall Polycarbonate, 5mm | 1.50 | 0.66 |
| TwinWall Polycarbonate, 4mm | 1.43 | 0.70 |
| Single Pane Glass, 3mm | 0.95 | 1.05 |
| TwinWall Polycarbonate, 6mm | 0.87 | 1.15 |
| Polyethylene Single Film Sheet | 0.87 | 1.15 |
| Fiberglass Glazing- Single Layer Panels | 0.83 | 1.20 |
For further Sciencey reading. Have a look here.
Appearance of Materials
For many people, the most important appearance requirement for Greenhouse owners is the desire to see in and out of the greenhouse. Your best option for this is Polycarbonate as it is the most transparent. Polycarbonate does wear over time and requires regular cleaning to keep it looking new and clear of anything that may cause scratches.
Longevity and Cost
The biggest greenhouse covering hassle with regard to longevity and cost is replacing a greenhouse covering. This makes it so important to choose something long-lasting. Polycarbonate, typically the most expensive greenhouse covering, has a warranty period anywhere from three to ten years, depending on the manufacturer (quality can vary greatly).
Although it is quite long-lasting, it can be difficult to replace because polycarbonate sheets come in limited sizes and are not easily cut. Therefore, you may be unable to find polycarbonate replacement sheets suitable for your particular greenhouse.
Solexx greenhouse covering, on the other hand, carries a ten-year warranty, is customizable and easily replaced, as well as less expensive. It can even come as a roll! Polyfilm plastic is a common greenhouse covering for people covering large greenhouses that are only being used seasonally. Although it is relatively inexpensive, it needs to be replaced yearly to every few seasons and tears easily in wind and hail. Great for your seasonal poly-tunnels and hop houses.
Find your size Poly-film sheeting here.
Ultimately, the right greenhouse for you is one which you will use for a long period of time – one which meets your demands and fits in with your lifestyle. Once you’re happy with your choice, read our guide on getting the most out of your new greenhouse. What works for some growers may not meet your requirements. More complex plans may be just up your alley, sometimes those plans can stifle success. Grow smart, not hard! Gardening advocates advise that you start with a basic, structure like a pop-up greenhouse so you can get the hang of your new plant responsibilities. The full-size challenges of Backyard Greenhouse gardening await! If you're looking for more in-depth greenhouse reviews or comparisons, click here to check out the top reviews.