Deciding Between Different Types of Greenhouse Glass

Greenhouse glass
Updated: October 11, 2019

Glass is the ideal material for covering a greenhouse, but when you’re shopping for greenhouse glass, you have several types to choose between. Some glasses are better for walls and others for roofs, based on how they’re designed and the stressors they can handle. Some greenhouse glasses can pose a serious cut risk if they break, so you need to balance your cost-savings with safety as you pick the glass for your greenhouse. These are the main types of greenhouse glass available and in common use:

Annealed glass – Annealed glass, the plain glass we’re all familiar with, is heat treated and allowed to cool in a controlled way so that the internal stresses relax slowly. Unfortunately, this means the glass is very weak and prone to cracking or breaking when the temperature on either side of the glass changes rapidly.  Annealed glass under pressure breaks into large, jagged shards, creating a hazard for anyone nearby. It’s the cheapest glass option and would work well for wall panels in a greenhouse where snow loads and high winds aren’t a concern.

Pros:

  • Annealed glass is the cheapest and most cost-effective glass option.
  • It is stronger than regular float glass and can handle a little pressure due to its treatment process.
  • This glass is great for low-traffic use or areas, and for use in places where it won’t be heavily exposed to heavy snow, high winds, or other inclement weather factors. 

Cons:

  • Because of how it handles the treatment process, this glass will shatter into sharp edges if damaged or broken.
  • Annealed glass shouldn’t be used for doors or greenhouse roofs, due to the increased potential for damage to happen in these areas from weather or excessive use.
  • The use of annealed glass may be subject to local or state building codes due to potential hazards of use. 

The best-rated annealed glass is from TroySys on Amazon. It can be bought at custom sizes, and is 100% satisfaction guaranteed. The manufacturer guarantees that your order will arrive perfectly intact, so you can order it to your specific needs and install it easily without worry.

Another great annealed glass, based on product reviews, is again from TroySys and is this square glass top. Like the rectangular option, the square glass is able to be ordered in customized sizes, and are guaranteed by the manufacturer to be exactly what you’re looking for and to arrive in one perfect piece. 

Tempered glass – Tempered glass is a heat-treated glass—the stresses in the glass are induced in a very specific way to increase the surface stress in relation to the internal stress. Tempered glass is very clear, but up to six times stronger than annealed glass and breaks into tiny, nearly square fragments that pose little risk to people. It’s a good choice for greenhouse roofs, walls and doors due to its ability to handle fluctuating temperatures, but shouldn’t be used on roofs where snow loads or high winds are a concern.

Pros:

  • Tempered glass is much stronger than annealed glass due to the extra processes of treatment it endures.
  • This type of glass can withstand temperatures up to approximately 470 degrees Fahrenheit. 
  • If it gets broken, this glass will shatter into small, granulated pieces that post no real threat of harm to people. 
  • Tempered glass handles temperature changes much better than annealed glass.
  • Tempered glass can be found in single- and double-tempered forms, and at varied tensile strengths.  

Cons: 

  • Tempered glass is more expensive than annealed glass, but is stronger and breaks more safely when damaged.
  • This type of glass may crack before completely breaking, and may affect the internal heat and humidity of your greenhouse.

There are a lot of tempered glass options you can choose from for your greenhouse. One of the best is the Spancraft flat edge tempered glass. It is 100 percent guaranteed and insured by the manufacturer to be delivered safely and on time. With that kind of promise, you can shop with a feeling of security and be sure that your product will arrive completely intact. 

If you need more customization with size options for your tempered glass, Fab Glass and Mirror has high-quality glass available in sizes ranging from 12 inches to 72 inches. There are no sharp edges to this glass since they bevel the edge to a flat edge and dull the edges. This means that you can handle and install it safely and without worry about accidentally cutting yourself on a sharp side. 

Laminated glass – Laminated glass is made of two or more sheets of glass bonded together using either an ethylene-vinyl acetate (EVA) or a polyvinyl butyral (PVB) layer—it’s the same glass your car’s windshield is made from. It’s extremely strong, like tempered glass, but unlike tempered glass, laminated glass doesn’t break. It may shatter, but the PVB layer holds the pieces together so they don’t pose a risk to anyone nearby.

This is a very good thing, especially when the glass is being used for a roof application where shattering may result in the rest of the panel or other panels falling to the ground. In addition, laminated glass can block up to 99 percent of incoming UV radiation, making your greenhouse safer for seedlings. Laminated glass is an excellent choice for greenhouse roofs—many people choose to use it for walls, as well, and the only major drawback to this is the additional cost over other glasses.

Pros:

  • If laminated glass is damaged, the PVB/EVA layer will hold the glass together. This makes it virtually impossible to get injured when handling the panel.
  • The PVB/EVA resin also keeps the window sealed, meaning your plants will not be damaged by any extra exposure while you get a new panel lined up to replace the damaged one.
  • Laminated glass is very resistant to high winds and harsh weather, and is arguably the safest option for the roof and door of your greenhouse, specifically.
  • Some laminated glass may also be soundproof, depending on the quality of the laminate material. 

Cons:

  • Laminated glass, due to its design and treatment process, is difficult to break. In cases of emergencies, you won’t be able to break the glass. 
  • Laminated glass is, without a doubt, the most expensive of the glass options for your greenhouse. 

If you’re looking for the best laminated glass options for your greenhouse, look no further than Fab Glass and Mirror’s selection of laminated safety glass. 

Fab Glass offers a variety of shapes, sizes, and edging for their laminated glass, so you can get your glass in any customizations that you want for your greenhouse. Their customer service team is well-regarded for any kind of problems that customers have had in the past, so don’t be afraid to reach out if there are any problems during or after ordering! 

You can also order custom cuts of tempered laminated glass from One Day Glass. Their shipping is free, insured, and guaranteed. Free shipping, especially when it’s insured, is great for ordering glass because of how fragile the product can be. You can rest assured knowing that your glass will arrive safe and sound, and if not that it will be replaced without a hassle!

A word about double-pane glass

Although it would seem that double-pane glass is the only way to go with a greenhouse, what works for homes isn’t always best for the hot, humid conditions inside a greenhouse. The seals inside a typical double-pane window are typically guaranteed for five to 10 years, but that guarantee is void if you install them in a greenhouse or indoor pool area. These areas accelerate the destruction of the seal, leading to premature failure and fogging. When it comes down to it, you’re much better off insulating your glass greenhouse with bubble wrap than spending the money on most double-pane products. At the end of the day, you can always take the bubble wrap down, but a busted seal in a double-pane unit means the whole unit must be replaced.

Buyer’s Guide to Greenhouse Glass

greenhouse glass and plant - types of greenhouse glass

Consider Where You Want to Place the Greenhouse 

You want to place your greenhouse in an area that isn’t surrounded by trees or in any deeply shaded areas. In an ideal situation, you want one of the longer sides of your greenhouse to face toward the south. This will allow the sun to cover the entire length of the greenhouse during the day, optimizing the amount of sunlight your plants will receive. 

It is also a good idea to have a water supply and electricity that will run into your greenhouse. This will allow you to have automated lights if necessary as well as a sprinkler system, which will help you with maintenance in larger greenhouses. 

You should also take the wind into account when setting up your greenhouse. If the wind typically blows in from a particular direction, you can almost always ensure what areas will offer ample ventilation into your greenhouse. 

Good ventilation will keep the air from stagnating and will provide your plants with access to fresh air, and will help to control temperature and humidity. It will also lessen the likelihood of diseases. 

Aspects That You Should Look for in Your Greenhouse

Quality of Materials: You know what kinds of glass you can choose from for your greenhouse now. Look for and choose a material that fits in well with your budget. If you can’t afford one material for the entirety of the greenhouse, it’s more than okay to mix and match supplies. 

If you use laminated glass for the roof and doors of the greenhouse, you can choose to save some of the cost of building by getting tempered glass for the sides of the greenhouse. You want to avoid using annealed glass for doors and the roof, but you can use it for the siding if your budget is particularly tight. 

You should always order more materials than you think you may need. After all, accidents happen and if you break a glass panel during installation, you won’t have to wait another week to continue construction. If all of your glass arrives intact and nothing breaks while you work, you can always use extra glass, especially annealed and tempered, as shelving within the greenhouse. 

Availability and Cost of Replacement Parts and Materials: This is something many people don’t really consider with any project, but one that should especially be taken into account when building a greenhouse. 

This doesn’t just account for any accidental breaks in the glass, either – this includes shelving, any extra systems you install and their respective parts, and any routine maintenance parts or work that may need to be done like welding damaged joints. 

Shelving, Floor Space, and Appropriate Support:  Again, you can’t go wrong with the “bigger is better” approach when it comes to a greenhouse. Nothing is worse than realizing you want just one more variety of plants in your greenhouse but lack the floor space or shelving and space for shelving. 

When installing shelves, make sure that they are properly supported. Mount them on the structural beams of the greenhouse and add standing support beneath them. This will optimize your space and, with the right supporting beams, you could even add more shelves beneath or above the initial shelf you wanted! 

How Large Should Your Greenhouse Be?

This depends on your chosen site. You don’t want to set up the greenhouse and then realize you didn’t account for as much space as you might have liked down the line, especially when any excess space can be used for other things. 

If you intend to add any passive or powered ventilation systems, a water pump or retainer, or anything else, extra space is necessary. But you may also just want to fill the entire greenhouse with a variety of plants. In either case, the best option would be to choose an ample site for your greenhouse, and then get the supplies or kit for the biggest greenhouse you can reasonably afford and set-up. 

If you just want a place to germinate seeds or protect saplings in and you find yourself on a tight budget, you could get away with a smaller walk-in greenhouse. But, if you want a bigger greenhouse that will be a permanent addition to your desired space and provide all the room you need to protect and grow whatever you like, then it’s worth the investment right off the bat.

Growing a Variety of Plants is Easy with a Quality Greenhouse

Since you can control the temperature, humidity, airflow, and water dispersion, you can grow pretty much anything in your greenhouse. Flowers, herbs, fruits, and vegetables can all be safely and effectively grown within a greenhouse. 

You can customize the inside of almost any greenhouse, especially one that you build yourself, with bench-height staging, higher shelving, and more to utilize as much space as possible. Just be sure during your planning that the plants you intend to grow will be able to receive the proper amounts of light, and that the greenhouse can maintain the appropriate internal temperatures and humidity to promote healthy growth. 

Buying Your Greenhouse Glass Online

cactus in greenhouse - types of greenhouse glass

When you buy anything, online or otherwise, you want to be sure you get your money’s worth. When ordering glass for your greenhouse, chances are you’ll be ordering it online, either from the manufacturer directly or through a third party, like Amazon. 

You want to make sure you understand the specifications of what you’re ordering, so consult a customer service representative if you need to during your ordering process to be sure that things like measurements and glass weight are accurate for your needs. 

A warranty or guarantee is also an important thing to look for. You are ordering glass – it is, by nature, a fragile product, and shipping isn’t always the most gentle process even when things are labeled. Make sure that the company you’re ordering your glass through has some kind of guarantee for safe delivery and arrival, or that they warranty their glass products in some way. That way if anything does happen, it isn’t you that loses out, and you can get a replacement as quickly and painlessly as possible. 

If you look and see that a company has both excellent customer service as well as a great guarantee or warranty, go a step further and check the reviews on the quality of the glass itself. Some glass may look or seem great online through pictures and descriptions, but if customers before you have purchased the product and were unhappy, you need to be aware of why. 

If you’re unsure of the measurements you need or want, or the thickness of the glass you want, check what other greenhouse owners and builders have said about the glass they’ve chosen and. You might want a thinner or thicker glass than someone else, but you should have an idea of what you’re looking for while you shop. 

Installing the Greenhouse

There are different ways to install your greenhouse once you have location and angle figured out and are happy with your plans. Make sure that if you have a kit, you follow the installation manual instructions carefully. Also, keep in mind to consult a local zoning authority on your greenhouse to be sure you don’t break any local laws during installation. 

Most manufacturers of greenhouses suggest pouring the concrete belt first and then attaching the greenhouse. You may also see the suggestion to mount the feet of the greenhouse and pouring the concrete around those to begin. 

If you’re building your greenhouse solely on your own, you can really use either of these methods depending on your own preferences, the area you’re installing the greenhouse in, and what you can reasonably manage to accomplish on your own.

If you are installing a tunnel greenhouse, you will probably want to dig a trench first to accommodate the struts that will need to be buried for security.

You do not have to lay concrete, necessarily, as your foundation. It is the sturdiest option, but it has its drawbacks as well. If the concrete isn’t textured, it can become slick easily, especially if you have a misting or sprinkler system. You will also need to add drains in the floor.

Alternatively, you could use some type of paver. These are fantastic for drainage purposes, but you may have unwanted weeds, vines, or grasses that will grow through the cracks and spaces. 

Pea gravel is a great choice. It allows the floor space to drain properly while keeping the surface area from becoming slick, muddy, or otherwise damp. 

Heating and Ventilation

Especially with winter in certain areas, making sure that your greenhouse has proper heating and insulation will make or break your greenhouse for the season. 

Glass does not naturally trap heat, so proper measures should be taken to ensure the safety and health of your plants over winter. There are three different ways you can keep your greenhouse over the winter months.

Cold: A cold greenhouse will provide your plants will shelter so that they don’t get frostbite under the snow, but that’s about all it will do. If you have alpine plants, they tend to thrive in these types of greenhouses, as you will not be adding heat to it. 

Cool: A cool greenhouse is a kind of a happy medium among the three options. It will keep the temperature above freezing, which will allow you to safely overwinter your plants in a frost-free environment. 

The best thing to do for a cool greenhouse is to install a thermostatically-controlled heater. This heater will only turn on when the temperature falls below the set parameters. It’s not only hands-free, it’s economical, as you won’t spend the extra money having the heater on consistently all season. 

This is the best option for annual plants that would otherwise need to be replaced. A cool greenhouse will extend your growing season, increasing yields. 

Heated:  A heated greenhouse gives you the ability to control the temperature. This means you will be able to grow practically anything that your space will comfortably permit, for as much of the year as you want or need to. 

Check with your manufacturer if you bought your greenhouse, and seek advice in forums and review boards online if you built it. Running a heater in a greenhouse all season is hardly economical, but there are measures that you can take to try to curb the costs and power use to keep your plants cozy. 

Otherwise, you can insulate your greenhouse. It won’t be pretty, but you can ideally use fleece or even bubble wrap to help insulate your greenhouse from the cold, and use a temperature-controlled heater to mitigate some costs. 

Ventilation is another important aspect to keep in mind. Plants of all kinds benefit from air movement and circulation, even in the winter months. You can use either a passive or a powered system for optimum ventilation. 

Passive: A passive ventilation system has no mechanical components. Passive ventilation happens during convection, which is when hot air loses density and rises, and vents through ridge vents in your greenhouse. Intake vents should be installed in the lower portions of the greenhouse side walls.

The biggest advantage of a passive ventilation system is that it is virtually silent. If your greenhouse is near or attached to your home, this is a great perk as you won’t have the loud buzzing sound of a fan system. 

The passive system has some notable disadvantages on its own. For example, it is not as efficient as a powered ventilation system. It also, surprisingly, costs as much as three to four times more to have a ridge vent system in place. Maintenance can also be daunting, as the ridge vent needs to be cleaned regularly, and the pistons of the vent need to be lubricated frequently. 

Powered: Powered ventilation, as the name implies, utilizes a powered fan and vents. The size of the fan will depend on the cubic feet of space that the greenhouse encloses.

The minimum goal is to overturn the cubic volume of air in the greenhouse in less than two minutes, but ideally in under a minute. The faster the turnover, the better the ventilation will be, and the easier it is to control temperature and humidity. 

Mounting the fan on the top of the wall opposite from the intake vents and door will ensure that fresh air entering the greenhouse travels throughout the building. The intake vents should be installed on either side of the greenhouse door, near the bottom of the wall. 

You can conveniently set this entire system up to work in-sync with itself. If you set it up with a thermostat, the fan or fans can automatically activate when a certain temperature is reached. The intake vents can also be activated in this way, opening when the fan is active and closing when it isn’t. 

You should also keep in mind that, regardless of a passive or powered system, you should take measures to circulate the air. Circulating the air helps to maintain temperatures and humidity, particularly in glass greenhouses, and also helps improve the structural integrity of your plants.

Deciding between glass and plastic? Read Glass greenhouse vs. plastic greenhouse—pros and cons>>

Kristi Waterworth

featured image: johnnyberg; image 1: Jackson Pokhrel: image 2: Scott Webb

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4 Comments

  • A very informative article! I was thinking about using a low-e glass for the greenhouse. What are your thoughts about that? I’ve researched that it doesn’t affect the visible light transmission but does reflect heat back to its source, so I am not quite sure if it’s good or bad for a greenhouse especially in the summer.

    Thanks!

    • Low e glass would not be a good idea as it only works with argon gas and in a sealed unit ,when used as a single piece of glass it rusts.

  • Off-line low-e glass can’t be used as a single piece of glass, but on-line low-e glass can. On-line low-e glass is much more stable than the off-line, but its efficiency is a little worse than the off-line.

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