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Are you in an area that freezes in the winter? We haven't had our greenhouse long, but we did have a single layer of plastic on the side walls for several months. Doubling up all the plastic layers made a significant increase in our over night greenhouse temps.

Yes, we freeze alright, down to -25F most winters. Ground freezes 4' down.

That's cold! Then for sure a single double layer of greenhouse plastic would serve your needs better than a single layer found on moat hoop houses.