Much anticipated, let’s discuss subarctic grade greenhouse insulation! Perhaps obviously, a greenhouse requires some creative insulation techniques. But, doing so is one of the major keys to operating a frost-free, semi-heated greenhouse!
The most impactful thing you can do is add a secondary layer to the greenhouse. Each layer increases efficiency, a lot! Perhaps surprisingly, it’s not the material itself that provides the insulation. It’s the air trapped in between those layers doing the insulative work!
In our case, our outer shell is standard corrugated greenhouse panels to provide structure and snow load. We then lined the interior upper portion of our greenhouse with UV rated plastic, similar to that installed on a hoophouse. This effectively traps heat and significantly slows down heat transfer into the second layer.
To attach the plastic, we’re using woven strapping cord. This isn’t purpose built, rather, this material is used to secure goods onto pallets. But, it gives us an excellent way to securely attach staples to the plastic without tearing it up.
This is, hands down, the most impactful thing we’ve done for shoulder season performance on our greenhouse. This is what gets you to heating for a couple bucks a day. It’s also huge in the summer, retaining more heat for longer periods. We’re glossing over a ton of detail, so we have a full length article on greenhouse insulation down in the comments.
It’s critical to know this upgrade also mandates excellent ventiliation for the summer months. A good general guideline is to have enough ventiliation to replace the entire greenhouse’s volume of air every minute. We have two fans, for redundancy, plus adquate air intakes to achieve that goal. They also feature louvers, reducing outdoor air exchange when the ventilation isn’t active.
The second most effective thing you can do is proper weather sealing around your door. Drafts are surprisingly detrimental to heat retention! We built a door stop that allowed us to get an excellent, firm seal against our door and it stopped all minor drafts. This was a surprisingly effective upgrade, well worth the cost of a bit of weather seal and a ripped 2×4.
Least effective, we have the 2 inch foam at the greenhouse base. Frankly, this isn’t worth the money and does very little heavy lifting. We do (maybe) see a little bit of better summer performance, since it does help build ambient heat. But, against freezing temperatures, the benefit is questionable.
There are other ways to achieve insulation of a greenhouse. Modern greenhouse panels are amazing, but expensive. But, hopefully this gives you a bit of food for thought! Tomorrow, we’ll discuss our actual greenhouse heating systems and thoughts around heat applications!
