Greenhouse glazing (greenhouse covering) lets the sunlight in while trapping warmth inside.
And that, after all, is what makes a greenhouse work.
If you’re a greenhouse gardener, light is your most precious resource.
In the low light days of winter, there’s just barely enough light to give many plants what they need (this varies, of course, depending upon your latitude).
But heat is also crucial.
A greenhouse must be able to trap heat inside that is generated by the sunlight entering the greenhouse.
That’s free heat, and without it a commercial greenhouse could not be viable, and a hobby greenhouse exorbitantly expensive.
So a perfect form of greenhouse glazing would allow sunlight to enter completely unimpeded while maintaining heat within the greenhouse with 100% efficiency.
There is no ‘perfect’ greenhouse glazing, of course. But the most commonly used glazing materials can be quite effective.
The glazings listed below are the most popular and most commonly used greenhouse coverings. They aren’t the only types of greenhouse coverings in use, of course.
Translucent fiberglass panels, for example, are used to some degree as a greenhouse glazing. But fiberglass panels have some problems (such as yellowing caused by sunlight) that make them less popular as a greenhouse covering.
Similarly, other materials that are used for covering greenhouses have some deficiency or obstacle (such as high cost) that prevents them from gaining widespread acceptance as a greenhouse glazing material.
The following, then, are the most commonly used materials. It’s likely that one of them is the very best choice for your greenhouse.
When you’re deciding upon the type of glazing for your greenhouse, there are many considerations. And some have little to do with the actual performance of the glazing.
For instance, the appearance of your greenhouse might be of great importance to you. Perhaps only certain greenhouse coverings will conform to ‘the look’ you have in mind for your greenhouse. Or perhaps cost will be an overriding factor in your decision.
But the following considerations have the most impact upon the performance of a greenhouse, and the cost and effort required to build, maintain and heat it. Here’s how the 3 most commonly used greenhouse coverings stack up against each other:
Light Transmission (as % of light allowed to pass through)
Insulating Ability (as “R” factor: higher number = better insulating properties)
The answer, of course, is that it depends.
It depends upon the look you want for your greenhouse. It depends upon your climate and what you’ll be growing in your greenhouse. It depends upon conditions your greenhouse will endure (high winds, high snow loads, high risk of hail). And for most of us, it also depends upon our budget.
The good news, though, is that when choosing a greenhouse covering for your greenhouse, it’s hard to make a really bad choice. Because in truth, all of the commonly used greenhouse coverings are quite effective.
But by understanding the strengths and weaknesses of each, hopefully you’ll be able to choose the very best greenhouse covering for your situation.