Glazing Choices: A Second Look at Double-Poly
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Just an addition to last week’s post on glazing choices for your passive solar greenhouse.
Curtis Stone, my friend, colleague, and a co-teacher in my greenhouse design course, has a 900 square foot space that grows roughly $50K in microgreens annually. His greenhouse uses a double-poly wall for glazing and it has worked exceptionally well in providing thermal protection for his crops all year long.
The double-poly wall has an R-value of 2 and costs 35 times less than a polycarbonate equivalent. It also can last up to seven years, which is nearly half as long as the lifespan of polycarbonate. The economic advantages are obvious: You can replace the polywall many times and still come out ahead in terms of cost.
Seeing Curtis’ greenhouse made me think more favourably of double-poly as a potential glazing choice. I do think there are situations where polycarbonate still wins out though. These would be in environments that have heavy snowfall and frequent chance of hailstorms.
In Calgary, we get hail almost every year. Every two to three years we see some golfball-sized stones. The stuff has enough force to crack windshields, and I’ve known friends who have been unfortunate enough to be caught in bad storms. Good design takes into account the fact that each ecosystem comes with its own factors and challenges.
So for me, in my neck of the woods in Southern Alberta, polycarbonate is still a relevant glazing choice, despite the price premium. When you are doing your own design, remember to take these larger macro factors into account because it can make the difference between success and failure. For more information, please check out the video below. Until next time!
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