OK, so this week we’re going to deep dive into cold climate greenhouses. Today, we’ll start with the the most important topic, the basics of greenhouse insulation!
Now, you probably have a fairly good idea of what insulation is. Clearly, in a greenhouse setting, traditional insulation materials are not going to work as we need light transparency. What’s truly important to understand about insulation is how it works. It’s not actually the insulation material that provides for warmth, it’s the fact that the material traps air that provides the warmth!
You see, in the world of thermal dynamics, temperature gradients can travel across most materials fairly quickly. But, when air sits between two materials, it takes quite some time to warm up or cool that “air barrier” in between those two materials. It is this property that allows insulation to be effective.
You’ll notice that our greenhouse has a “hard shell” exterior layer. That’s great for protecting our greenhouse from heavy snow loads and intense rainfall. While this shell by itself does provide some insulative value, it’s not particularly great at that on its own.
So, what we did was we lined the inside of our greenhouse with UV rated plastic, like what you’d put on a hoophouse. This does two things. First, it seals the greenhouse and heavily reduces direct outdoor air exchange. But, it also traps several inches of air between the plastic layer and the outer hard shell. Effectively creating insulation!
Now, if you just go stapling plastic to any old surface, you’ll quickly learn that those staples will quickly rip out. We used a woven cord, typically used for securing materials on pallets, that allows us to better secure those staples to the plastic. This method has held up for years now and we’ve been quite pleased with it.
Since this plastic isn’t “form fit,” you do have to be a little creative in your folding techniques and methods for containing excess plastic. We did the best we could, given it was our first try at this. Fortunately, prettiness of the install has zero impact on performance!
The one “gotcha” to insulating a greenhouse like this is you absolutely need great ventilation. If you insulate a poorly ventilated greenhouse, you’re building a plant cooker! Passive vents may not be enough, plus those are basically sieves for air exchange! Good air intakes and active ventilation with fans will be best.
What we’d tell you is this is the very best upgrade we’ve done to our greenhouse, hands down. It’s enabled us to use the greenhouse in the shoulder seasons, heating it with a rather inexpensive space heater. It’s also greatly improved summer performance, too, as it helps us maintain warmer temperatures for longer periods of time. Cost-wise, it’s not terribly expensive to do, either. Especially given the performance gains!
We also have a full build guide on this topic, in the event you want to dive deeper and explore a similar solution. You’ll find it linked down in the comments.
