Best Glass For A Greenhouse

What Is The Best Glass For A Greenhouse?

In Glazing by Ana M

Glass has always been a traditional option for a greenhouse mainly because of its aesthetics. It also was the only one option available at the time.

Now, with the ability of plastic variations glass glazing is not on the top of the game but still has its advantages. There are 6 greenhouse glazing materials that you can use, but in this post, I will talk about different types of glass glazing.

So, what is the best glass glazing for a greenhouse?

The best glass glazing for a greenhouse is double pane tempered glass. It is robust, and in case of damage, it breaks into small square pieces, so the chances of injury are low and small parts won’t damage your plants.

What glass is used in greenhouses?

  • Horticultural glass
  • Toughened glass
  • Heat-strengthened glass
  • Insulated glass
  • Tempered glass
  • Laminated glass

Horticultural Glass for A Greenhouse

Horticultural is a standard glass of 3mm thickness. It is also known as annealed glass. Basically, it is the lowest type of glass which can be used for a greenhouse.

Therefore, it is the cheapest glass option. The major drawback of annealed glass is that it is extremely fragile. You must either avoid kids playing in the garden with a ball which can break your precious glass or get a toughened version of the glazing.

When talking about the breakage, annealed glass is hazardous as it breaks into long sharp shards capable of hurting people nearby. So, in terms of safety, I would consider toughened versions which I am discussing below.

Toughened Glass Greenhouse

Apart from the good looking greenhouse, you need to think about its durability and safety. For these reasons to toughen the glass, two processes can take place. These are heat-strengthening and tempering.

The two techniques are based on the heat-treating of the glass but differ in the cooling process leading to the differences in strength. In both cases, untreated glass is heated to around 1200˚F and cooled down, creating surface and edge compression.

Heat-Strengthened Glass Greenhouse

To make the heat-strengthened glass, the cooling stage is slowed down, leading to the lower compression strength. In comparison to the annealed glass of the same thickness, the heat-strengthened glass is two times stronger.

When broken, the glass cracks in a pattern similar to the annealed glass and stays in the frame for longer, so, it is unlikely for it to fall and injure people nearby or to damage your plants.

REMEMBER! Heat-strengthened glass is NOT a safety glass according to the building codes.

Is Tempered Glass Good For Greenhouse?

In the case of the tempered glass, the cooling stage is much faster to achieve higher compression strength. In comparison to the untreated glass of the same thickness, the tempered glass is from 4 to 5 times more robust.

When broken the glass cracks into small pieces and typically falls instantly from the frame which is not ideal for a greenhouse as it can damage your plants.

Tempered glass is a safety glass according to the building codes. These two options are great alternatives for the replacement of the annealed glass.

However, in terms of safety and durability, I would consider laminated or insulated glass options.

Laminated Glass Greenhouse

Laminated glass is referred to as the Grade A safety glass. It consists of two pieces of glass joined together with an interlayer in between. When broken, the glass doesn’t break into long sharp pieces and doesn’t fall from the frame.

The broken glass attaches to the interlayer usually made of polyvinyl butryal or resin forming a ‘spider web’ cracking pattern. Therefore, it won’t hurt someone and won’t damage your plants.

However, I have never tried a laminated glass. Mainly because of the concerns with the leaks. So, if you have tried the laminated glass, please let me know what you think in the comments section.

Insulated Glass Greenhouse

Insulated glass is made of two or more sheets of glass held together with the dry air space between them. You can make an insulated glass yourself with annealed, heat-strengthened or tempered glass and increase their insulation performance.

How does insulated glass work?

Usually insulated glass is double glazed meaning it consists of two panes of glass, however triple pane is becoming more popular due to the increasing energy costs.

So, if you want to assemble an insulated glass yourself or to buy one consider the following points:

  1. Simply take clean two sheets of glass of the same size and place a spacer between them.
  2. A spacer is usually a metal or polymer strip with a drying agent like desiccant which absorbs moisture formed in the space between the sheets of glass.
  3. The ideal space between the glass sheets should be from 10 to 20 mm, the minimum space is better for a good thermal performance.
  4. The glass sheets are fully sealed, so the empty space with dry air between them is an insulator which limits the movement of cold air to the greenhouse.
  5. For better insulation (higher R value) a low conductivity inert gas like argon can be used to fill this space.

Insulated glass is a good choice for a greenhouse, so if you decided to purchase one or make it yourself I would recommend to go for tempered glass due to the safety concerns.

How thick should greenhouse glass be?

Double pane (a glass pane is 4mm thick) greenhouse glass is thick enough and triple pane is really expensive and unnecessary for a greenhouse. However, after checking the guarantee for the seals of the double-glazed glass, these are guaranteed to last from 5 to 10 years.

Also, it is applicable only for the use at home. The environment of the greenhouse will destroy the seal quickly. There are few more cost-effective glass options to choose from.

Can I use Low-e glass in a greenhouse?

The use of low-e coating can reduce the amount of lost heat by 30 per cent compared to the annealed glass in a greenhouse. However, it does lose from 5 to 10 per cent of visible light transmission.

The glazing technology has improved dramatically to battle the rising energy costs. Special coating for glass is used to raise the energy efficiency.

One of them is a low-emission (low-e) coating which has gained popularity among the gardeners.

So, what is a low-e glass?

It is a clear single pane glass coated into a thin layer of metal oxide which is applied microscopically.

Low-e coating is eliminating dangerous for plants UV light and infrared light whilst letting through visible light and photosynthetically active radiation (PAR) useful for plants.

Moreover, low-emission coat reflects the heat back to its source. For example, in winter when heat from a greenhouse tries to go through, the glass outside low-e glass reflects it back inside. The opposite effect takes place in the summer.

What is the best glass glazing for a greenhouse roof?

The best glass glazing for the roof would be an insulated glass with the laminated glass pane on the outside and tempered glass on the inside. The laminated glass will hold the load of snow and won’t break into tiny little pieces and will stay in place.

Hope that you found this blog post useful 🙂

Are you using glass for your greenhouse panels?

Please let me know in the comments section below if you do or why you don’t.

Want more greenhouse tips, tricks, and ideas? Follow me on Pinterest!

Happy Greenhousing 🙂

With Love,


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