Selecting the ideal covering material for your greenhouse is one of the most important decisions a grower can make. The covering impacts light transmission, insulation, durability, and cost – all factors that affect the functionality and controlled environment of your greenhouse.
This epic guide compares the most common greenhouse covering materials on the market today:
We’ll analyze the pros and cons of each material type to help you determine the right solution for your greenhouse needs and budget.
Table of Contents
Light Transmission Properties
The covering material plays a major role in controlling light quality, quantity, and distribution inside your greenhouse.
Light transmission refers to how much natural sunlight the material is able to pass through into the greenhouse interior. A highly transparent covering maximizes the light available for your plants.
The table below compares light transmission percentages of common greenhouse covering materials:
| Covering Material | Light Transmission Percentage |
|---|---|
| Glass | 90% |
| Polyethylene Plastic Film | 88% |
| Polycarbonate | 86% |
| Acrylic | 92% |
| Fiberglass | 90% |
Glass and acrylic tend to have the highest light transmission, followed closely by polyethylene film and polycarbonate.
Light diffusion is also important for evenly distributing sunlight to avoid hot spots. A slightly diffusive material can be preferable to completely clear.
Coverings like acrylic and polycarbonate have good light diffusion properties that bend and scatter light rays. Glass and polyethylene film have lower diffusion. Diffusive coatings can be applied to glass to improve light scattering.
Over time, plastic film coatings degrade, reducing light transmission. Replacing films every 3-4 years can maintain optimal light conditions.
Key Takeaways – Light Transmission
- Acrylic and glass provide the highest light transmission into greenhouses
- Polyethylene film offers good transparency at a lower cost
- Polycarbonate and acrylic offer ideal light diffusion properties
- Plastic films require replacement every few years as coatings degrade
Insulation Value
Greenhouse coverings play a crucial role in temperature management and heat retention. Materials with higher insulating values (R-values) reduce heat loss and energy costs for heating.
This table compares the R-values of common greenhouse covering materials:
| Covering Material | R-Value |
|---|---|
| Glass | 1.05 |
| Polyethylene Plastic Film | 1.15 |
| Polycarbonate | 1.20 |
| Acrylic | 1.47 |
| Fiberglass | 1.04 |
Higher R-value = Better Insulator
As the data shows, acrylic offers the highest R-value, followed by polycarbonate. Glass and fiberglass are the lowest.
Double-inflated greenhouse poly films add an additional layer of trapped air for significantly higher insulation. Adding a double layer can reduce heat loss by up to 30%.
Proper inflation levels must be maintained for maximum R-values. Added insulation also helps moderate interior temperatures at night when plants are vulnerable to cold.
Key Takeaways – Insulation
- Acrylic and polycarbonate offer the best insulation properties
- Double-layer inflated polyethylene films also provide excellent insulation
- Higher insulation reduces greenhouse heating costs and improves temperature moderation
Weather Protection
Greenhouse coverings must withstand the elements including hail, heavy snow loads, and high winds. Materials that resist weather damage reduce replacement costs and greenhouse downtime.
Impact Resistance
- Glass – Low impact resistance. Hail and debris can shatter glass.
- Polyethylene Plastic Film – Medium resistance. Small tears can develop over time.
- Polycarbonate – Highly impact-resistant. Withstands hail and debris.
- Acrylic – Medium-high impact resistance though less than polycarbonate.
- Fiberglass – Medium impact resistance, but less than polycarbonate.
Snow Load Capacity
The amount of accumulated snow a covering can withstand without buckling or collapsing depends on:
- Material strength
- Ribbing/framing
- Slope of greenhouse roof
- Local snowfall levels
In heavy snow regions, polycarbonate, acrylic, and fiberglass can withstand high snow loads, especially with sufficient roof sloping. Poly films may require extra ribbing support when snow loads exceed 20 pounds per square foot.
Wind Resistance
Covering resistance to high wind gusts relies on similar factors as snow load capacity. Additionally:
- Fastening method and frequency
- Wind permeability – ability to allow some air passage through material
- Reinforced films, polycarbonate, or rigid sheets resist deformation
Proper installation is key for wind resistance. Greenhouse infrastructure should be rated for local wind conditions. Some materials like poly film allow excess air to pass through, preventing billowing.
Key Takeaways – Weather Protection
- Polycarbonate offers the best all-around protection from hail, snow, and debris
- Poly film withstands weather but requires reinforcements in extreme conditions
- Proper greenhouse structure and installation also determines weather resistance
Durability and Lifespan
The anticipated lifespan of your greenhouse covering material impacts long-term costs and replacement frequency. Some key durability factors include:
- Tensile strength and tear resistance
- UV light degradation resistance
- Clarity over time
- Ease of repair
Here are the typical lifespans of common materials:
| Covering Material | Lifespan |
|---|---|
| Glass | 15-20 years |
| Polyethylene Plastic Film | 3-4 years |
| Polycarbonate | 10-15 years |
| Acrylic | 5-10 years |
| Fiberglass | 10-15 years |
Glass, polycarbonate, and fiberglass last the longest. Acrylic and poly films require more frequent replacement.
However, small poly film tears can be repaired inexpensively with tape, avoiding full sheet replacement. Other rigid sheets usually must be replaced fully when damaged.
Plastics like polycarbonate and acrylic resist UV degradation relatively well. Poly films require UV-inhibiting coatings to slow light damage over time.
Key Takeaways – Durability and Lifespan
- Glass, polycarbonate, and fiberglass coverings offer the longest working lifespans
- Poly films require frequent replacement but allow easy spot repairs
- UV inhibitors and quality installation extend plastic sheet lifespan
Cost Comparisons
Greenhouse covering costs vary widely by material type and size:
| Covering Material | Cost Per Square Foot* |
|---|---|
| Glass | $15 – $40 |
| Polyethylene Plastic Film | $0.40 – $1 |
| Polycarbonate | $1.50 – $7 |
| Acrylic | $2 – $5 |
| Fiberglass | $3 – $7 |
*Cost ranges account for material grade and thickness
Poly films offer the lowest upfront costs by far per square foot. However, their short lifespan increases replacement frequency and long-term costs.
Glass is generally the most expensive covering material, though lower grades can be affordable. It offers good value over its long working lifespan of 15-20 years.
Rigid plastics like polycarbonate and acrylic are mid-range in price but tend to last 5-15 years before replacement. Their excellent insulation properties can yield heating and cooling energy savings that offset higher initial material costs.
Key Takeaways – Costs
- Poly films have the lowest upfront costs per square foot
- Longer-lasting materials like glass and polycarbonate pay off over time
- Added energy savings from insulation should factor into cost analysisSpecialty Greenhouse Covering Materials
Beyond standard glass, plastic films, and rigid sheets, some specialty greenhouse covering materials offer unique properties. Let’s take a deeper look at corrugated polycarbonate, structured polycarbonate, and ETFE films.
Corrugated Polycarbonate Panels
Corrugated polycarbonate features ridges and grooves that create air chambers within the material. This twin-wall or triple-wall construction provides significantly higher insulation value than solid polycarbonate sheets.
- Insulation Value – R-values between 1.3 to 1.59. Reduces heat loss by up to 50% compared to solid polycarbonate.
- Light Transmission – Typically between 82-86% light transmission. The ridges diffuse light evenly.
- Durability – Estimated 10-12 year lifespan. Resists impact, snow loads, and UV degradation. Easy to install.
- Cost – $1.50 – $5.50 per square foot, comparable to solid polycarbonate sheets. A cost-effective rigid plastic option.
Corrugated polycarbonate excels in small to mid-size greenhouses needing good insulation, light transmission, and affordability. The compact sizing is ideal for hobby greenhouses.
Structured Polycarbonate
Structured polycarbonate sheets contain integrated ribs that create hollow internal air chambers within the material. This enhances insulating value significantly.
- Insulation Value – R-value around 1.59, reducing heat loss by up to 50%
- Light Transmission – 85-89% light transmission depending on thickness.
- Durability – Estimated 10+ year lifespan. Withstands weathering and yellowing.
- Cost – $4 – $6 per square foot. On the higher end for polycarbonate.
The combination of light transmission, insulation, and durability make structured polycarbonate sheets ideal for large commercial greenhouses. The higher cost limits use in smaller DIY greenhouses.
ETFE Film (Ethylene Tetrafluoroethylene)
ETFE is a transparent fluoroplastic film that offers extremely high light transmission and weather resistance.
- Light Transmission – 95%+ light transmission. Crystal clear material for maximum light.
- Insulation Value – R-value between 1.4 – 1.5. Not as insulating as polycarbonate.
- Durability – Estimated 20+ year lifespan. Withstands UV, condensation, tears. Self-cleaning.
- Cost – $4 – $8 per square foot. Only suited for high-budget commercial greenhouses.
The high cost and lower insulation value limit ETFE films mainly to commercial arched-roof greenhouse structures in mild climates needing ultimate light transmission.
Key Takeaways
- Specialty polycarbonate offers light diffusion, insulation, and durability at a moderate cost
- Structured polycarbonate excels in large professional greenhouses
- ETFE provides superior light transmission and weather resistance for mild climates
- Consider specialty materials only for specific added benefits due to high costs
Conclusion
Selecting the right greenhouse covering involves weighing many factors of performance, cost, and value over the material’s working lifespan.
For professional growers, glass and polycarbonate tend to provide the best overall utility. Home growers can often find the most value in lower grade glass, twin-wall polycarbonate, or multi-layer poly film.
Acrylic sheets offer smaller scale growers a lightweight and insulating rigid plastic option. Fiberglass is durable though lower in insulation than other rigid plastics.
No matter the material, proper greenhouse design, construction, and maintenance practices extend covering lifespan and functionality. Investing in quality materials upfront saves money over time.
This guide can help growers compare key metrics and make the ideal greenhouse covering decision for their needs and operating conditions. For additional guidance in selecting greenhouse coverings or designing your structure, check out Farmyonder’s resources below:
- Greenhouse Kits – Our selection of top-quality DIY greenhouse packages.
- Greenhouse Planning Guide – Considerations and tips for planning your greenhouse build.
- Greenhouse Gardening for Beginners – Getting started growing in a greenhouse.
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