Greenhouse windows are an essential component of any greenhouse structure. They allow natural sunlight to enter the greenhouse, provide ventilation, insulation, and protection from the elements. Choosing the right greenhouse windows and glazing materials involves carefully considering factors like climate, budget, durability, and ease of maintenance. This article provides a comprehensive overview of greenhouse windows, including different types, glazing options, installation, and tips for selecting the optimal windows for your needs.

What are Greenhouse Windows?

Greenhouse windows, also known as glazing, are transparent or translucent materials installed in the walls and roof of a greenhouse. They allow sunlight to enter the structure to facilitate photosynthesis and plant growth. The glazing also traps heat inside the greenhouse, creating a warmer microclimate for the plants while protecting them from harsh exterior conditions.

Greenhouse windows serve several important functions:

Letting in sunlight: The glazing materials allow sunlight to penetrate into the greenhouse. This light is vital for photosynthesis and warming the interior space. Different glazing materials transmit sunlight to varying degrees.
Trapping heat: The windows act as insulators, trapping heat that builds up inside the greenhouse during the day and releasing it slowly at night. This creates ideal growing conditions for plants.
Providing ventilation: Most greenhouse windows can open to allow for air circulation. Proper ventilation prevents excessive heat and humidity buildup.
Protecting from the elements: Glazing shields plants from external factors like wind, rain, hail, snow, and cold temperatures.
Durability: Quality greenhouse glazing is impact and scratch resistant. It can withstand years of exposure to sun, rain, and hail.
Aesthetics: Glazing provides clear views into and out of the greenhouse. Some options like tinted, reflective, or patterned glass can affect visibility.

Choosing suitable greenhouse windows is one of the most important decisions when building or upgrading a greenhouse. The right windows help optimize light transmission, insulation, durability, and aesthetics.

Types of Greenhouse Windows

There are several different types of greenhouse windows available. The optimal choice depends on climate, budget, and desired features.

Glass

Glass is the traditional glazing material used in greenhouses. Different types include:

Regular glass – Standard clear soda-lime glass used in many older greenhouses. It transmits about 90% of light but is not very energy efficient. Regular glass is also breakable and heavy.
Tempered glass – This treated glass is 4-5 times stronger than regular glass. It resists breakage and temperature changes.
Laminated glass – Two or more glass sheets bonded together with an interlayer. The interlayer holds broken glass in place if fractured. Laminated glass insulates well and reduces noise.
Low-iron glass – Contains less iron than regular glass, resulting in exceptional clarity and light transmission. Ideal for environments needing abundant light.
Tinted/reflective glass – Tinted in various colors to filter light and reduce glare. Reflective coatings improve insulation. Visibility is impaired with darker tints.
Patterned glass – Decorative pressed glass with translucent patterns to diffuse light. Visibility is limited but excellent light scattering provided.

The benefits of glass include durability, clarity, and ease of cleaning. Drawbacks are weight, cost, and breakability. Tempered, laminated, or patterned glass are good choices to improve safety and insulation while letting in light.

Plastic Glazing

Plastic glazing materials are commonly used in greenhouses today. Options include:

Polyethylene (PE) film – Lightweight and economical PE sheeting provides good light transmission but degrades over 1-3 years.
Polyvinyl chloride (PVC) – More durable than PE film, PVC can last over 5 years. PVC is available in single or double layers.
Polycarbonate – Extremely strong multiwall or corrugated panels. Polycarbonate insulates well and lasts over 10 years. Can withstand some hail damage.
Acrylic – Transparent rigid acrylic sheets provide excellent light transmission and insulation. Acrylic is more scratch and UV resistant than polycarbonate.
Fiberglass reinforced plastic (FRP) – FRP panels incorporate fiberglass for extra impact resistance. They insulate well but are not as strong as polycarbonate.

Plastics offer affordable options that are lightweight, insulative, and long-lasting. Polyethylene works well for temporary seasonal structures. Polycarbonate and acrylic are better choices for permanent greenhouses needing maximum durability.

Composite Materials

Some composite glazing products combine plastic and glass:

Glass reinforced polyester – Layers of glass and polyester fused together. Very durable and impact resistant. Excellent at handling temperature fluctuations.
Polycarbonate multiwall sheet with glass – Combines polycarbonate’s strength with glass’s clarity and insulation. Withstands high impacts while letting in abundant natural light.
Glass bonded to acrylic or polycarbonate – Glass exterior for strength and scratch resistance. Plastic interior layer insulates and prevents shattering.

Composite glazings provide the benefits of different materials in one product. They have high visibility, insulation, and durability ratings. Composite options are also lighter than glass.

Glazing Comparison Chart

This comparison chart summarizes the performance characteristics of common greenhouse glazing materials.

Glazing Options by Climate

Greenhouse windows should be selected while keeping local climate conditions in mind. Some materials are better suited for certain environments.

Cool & Humid Climates

In cool, humid climates prone to cloudy conditions, prioritize materials that maximize light transmission:

Low-iron glass
Acrylic
Polycarbonate
Glass + plastic composites

Ventilation is also important in humid areas. Operable windows or roof vents allowHumidity control and air circulation. Avoid condensation buildup by selecting glazings with anti-drip coatings.

Hot & Dry Climates

Insulation and heat retention are more important in hot, arid regions. Look for materials like:

Tempered glass – resists temperature changes
Double-layer polycarbonate or acrylic – higher insulation value
Glass, acrylic, polycarbonate composites – combine insulation and clarity.

Tinted or reflective glazing can help reduce glare and overheating during intense sunlight. Proper shading is also recommended for extremely hot climates.

Cold Climates

Priorities for colder regions are insulation, durability, and condensation resistance:

Laminated glass – insulates against heat loss
Polycarbonate – withstands heavy snow loads
Acrylic – resists interior condensation
Glass-reinforced polyester – handles freezing temps

Avoid single pane glazings with poor insulation. Double pane or multiwall plastic panels work best for minimizing heat loss in cold climates.

Coastal Regions

Coastal greenhouses need windows that can endure salt, wind, and humidity:

Tempered glass – resists breaking from wind pressure
Acrylic – blocks UV rays that degrade plastics
Polycarbonate – withstands oceanfront corrosion
Composite glazings – protect against salt damage

Frequent cleaning is recommended near oceans to remove salt deposits. Avoid iron framing which can corrode quickly in coastal conditions.

Other Glazing Considerations

Beyond basic climate factors, also weigh the following:

Budget – Glass is generally the most expensive option. Multiwall polycarbonate and acrylic panels are moderately priced. Polyethylene film is the most affordable but shortest-lived.
Light needs – Leafy greens, flowers, and fruiting plants need ample light transmission. Prioritize low-iron glass, polyethylene, polycarbonate, or acrylic.
Lifespan – Glass lasts indefinitely. Plastics degrade over time from UV exposure. Polyethylene film lasts 1-3 years while polycarbonate and acrylic may last over 10 years.
Appearance – Glass maintains excellent clarity and visibility. Plastics can become hazy over time, impairing views. Tints also reduce visibility.
Fire rating – Polycarbonate and acrylic panels are self-extinguishing. Plastic glazings often require a fire barrier during installation.
Chemical resistance – Some fertilizers, cleaners, or pesticides can damage plastics. Always check chemical compatibility.
DIY vs professional install – Glass and polycarbonate panels often require professional installation. PE films and corrugated polycarbonate sheets can be DIY-friendly.

Carefully weigh all these factors when selecting greenhouse glazing. This helps ensure you choose the optimal materials for your specific needs and environment.

Glazing Installation Tips

Proper installation is critical for effective greenhouse windows. Follow these tips:

Place glazing on the north wall to avoid intense midday light. East, west, and south walls should have the most glazing.
Slope glass panes at a 40-45° angle to maximize light capture and minimize dust buildup.
Ensure all glazing and framework is securely fastened and sealed according to manufacturer specifications to prevent heat loss. Use structural silicone for glass installations.
Overlap and secure polyethylene films properly to prevent tears and billowing during windy conditions.
Allow for thermal expansion and contraction of panels during installation. Leave a bit of wiggle room in framing.
Use condensation control films and venting to reduce moisture accumulation between dual panes.
Wear protective gear when handling glass panes and plastic sheets to prevent accidental breakage, scratches, or cuts.
Hire professionals for glass greenhouse construction or replacements. Improper glass installation can lead to weak framing, breakage, and heat loss.

Taking the time to correctly install greenhouse windows ensures they will perform optimally for many years.

Greenhouse Window Maintenance

Regular maintenance keeps greenhouse glazing in peak condition:

Wash glass and plastic panels frequently using mild cleaners to remove dust, salt, and mineral deposits that reduce light transmission. Avoid abrasive brushes or pads.
Inspect all glazing and framework annually for signs of deterioration like clouding, cracks, leaks, or loose frames. Replace compromised glazing immediately to maintain optimal insulation and light levels.
Reapply UV-protective films to plastic glazings as directed to extend lifespan.
Use razor blades to carefully scrape away hard water stains on glass.Restore clarity and light penetration.
Caulk around all glazing with high quality material to seal any gaps. Check caulking every few years and reapply fresh beads as needed.
Lubricate any window or vent hinges, pulleys, and mechanisms annually to prevent seizure or breakage.
Remove snow buildup frequently to avoid excessive weight on glazing. Use soft bristle brushes instead of scrapers to protect the surfaces.
Control interior humidity levels through proper watering, venting, and dehumidification to minimize condensation on glazing.

Consistent maintenance helps maximize the working life of greenhouse windows, ensuring ongoing optimum growing conditions for crops.

Choosing the Best Greenhouse Windows

Selecting suitable greenhouse windows involves assessing many factors:

Climate – Match glazing to local environmental conditions like humidity, temperatures, wind, and snow loads.
Budget – Glass is costliest but extremely durable. Multiwall polycarbonate and acrylic strike a balance between affordability and longevity.
Light transmission – Maximize light for plants with low-iron glass, polycarbonate, acrylic, and some composite panels.
Insulation – Double-layered polycarbonate, acrylic, composites, and certain glass types provide excellent insulation.
Durability – Glass withstands decades of use. Heavy-duty polycarbonate and composites last over 10 years. Acrylic also endures well.
Fire resistance – Look for self-extinguishing plastics or composites.
Ease of installation – Professional help needed for glass. Polycarbonate and polyethylene sheets can be DIY-friendly.

There is no universally “best” greenhouse glazing. The optimal product depends on individual needs and growing environment. Working with a reputable greenhouse supplier ensures you select the right windows for maximum plant growth, production, and longevity.

Frequently Asked Questions About Greenhouse Windows

Greenhouse glazing is a complex topic. Here are answers to some common questions about greenhouse windows:

What is the best glass for a greenhouse?

For glass greenhouses, tempered glass, laminated glass, or low-iron glass are good choices. Tempered glass is 4-5 times stronger than regular glass. Laminated glass insulates well and resists shattering. Low-iron glass provides the highest light transmission.

Is acrylic or polycarbonate better for a greenhouse?

Both materials have benefits. Acrylic sheets offer crystal clarity and resist scratches. Polycarbonate panels are extremely impact resistant. Acrylic insulates slightly better while polycarbonate withstands hail and other impacts more effectively.

How long does polycarbonate last in a greenhouse?

With proper installation and maintenance, multiwall polycarbonate panels can last over 10 years in greenhouse conditions. Look for UV-protected panels rated for at least 10 years.

What thickness of polycarbonate is best for a greenhouse?

For roof panels, 16mm triple-wall or 32mm multiwall polycarbonate provides excellent insulation and durability. Wall panels can be thinner like 8mm twinwall polycarbonate which still insulates well.

Should a greenhouse face north or south?

Ideally, orient the greenhouse with the long axis running east to west to provide equal sun exposure. South-facing walls should have the most glazing to maximize winter solar gain. Avoid too much glazing on the north for controlled conditions.

How much greenhouse window area is needed?

There is no universal rule, but a minimum of 45-55% of the total greenhouse area should be glazing. Leafy greens need 50-60% glazing while tomatoes, peppers and vines need 40-45% glazing. The optimal ratio balances light transmission with insulation.

Do greenhouse windows need shading?

In very hot climates, shade cloths, screens or tinted glazing may be needed to reduce intense summer heat. Approximately 30% shade coverage is usually ideal. Remove shading in cooler months to allow full light transmission.

How often should greenhouse glazing be cleaned?

Clean glass and plastic glazing at least 2-4 times per year. Cleaning every 1-2 months is even better for maximum light transmission. Use soft cloths, gentle cleaners, and avoid abrasives.

When should old greenhouse glass be replaced?

Look for hazy panels, severe scratches, cracks, chips or extensive caulking deterioration. Also replace glass that has noticeable condensation between panes. These issues indicate failing glass that should be replaced for top performance.

Conclusion

The selection, installation, and maintenance of greenhouse windows significantly impacts the performance of any greenhouse. After assessing factors like climate, budget, and crops, choose glazing that balances durability, light transmission, and insulation. With routine cleaning and vigilance for any deterioration, quality greenhouse windows will provide optimal growing conditions for many years. A greenhouse is a valuable investment, and devoting time to understand and care for the glazing will pay dividends through thriving plants and heavy yields over multiple growing seasons.

All About Greenhouse Windows

Introduction

Greenhouses allow gardeners to grow plants in controlled environments protected from external weather conditions. The windows, known as glazing, are a critical component that influence the light, temperature, humidity, and overall performance within the greenhouse. This article provides a detailed overview of the different types of greenhouse windows, considerations for selecting glazing, proper installation, and maintenance tips to optimize functionality and plant growth.

Types of Greenhouse Windows

Greenhouse windows are available in glass and various plastic materials. Each has advantages and drawbacks:

Glass

Regular, tempered, laminated, wired, etc.
Pros: Excellent durability, high light transmission
Cons: Heavy, prone to breakage, higher cost

Polyethylene (PE) Film

Multi-layer PE plastic sheeting
Pros: Very affordable, easy installation
Cons: Degrades quickly (1-3 years lifespan)

Polyvinyl Chloride (PVC)

More rigid plastic panels
Pros: Low cost, 5-7 year lifespan
Cons: Hazy over time, less insulation

Polycarbonate Panels

Multi-wall or corrugated extruded plastic
Pros: Extreme impact resistance, good insulation, 10+ year lifespan
Cons: Expensive, prone to scratching

Acrylic (PMMA)

Rigid transparent acrylic sheets
Pros: Excellent light transmission, highly weather