We’re in a fairly temperate 8b climate zone, but I like to grow tropical plants and it does dip below freezing at times. And last year it was down in the teens for hours at a time. My citrus had no chance in those conditions.
We are lucky enough to have a wonderful South-facing screened porch though and with a little effort, I was able to make it into a greenhouse:
We used some double-sided tape and some 4mm poly to cover the screen:
And it’s working pretty well—generally about 15 degrees warmer in the green house.
We do have the added benefit of the skylights, which allow more sun in from above and that may help:
The skylights are great also because we get sunlight in the middle of our house during the winter, which is crucial to stave of seasonal affected disorder!